1 | /* |
2 | * Copyright (c) 2021 Apple Inc. All rights reserved. |
3 | * |
4 | * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ |
5 | * |
6 | * This file contains Original Code and/or Modifications of Original Code |
7 | * as defined in and that are subject to the Apple Public Source License |
8 | * Version 2.0 (the 'License'). You may not use this file except in |
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10 | * may not be used to create, or enable the creation or redistribution of, |
11 | * unlawful or unlicensed copies of an Apple operating system, or to |
12 | * circumvent, violate, or enable the circumvention or violation of, any |
13 | * terms of an Apple operating system software license agreement. |
14 | * |
15 | * Please obtain a copy of the License at |
16 | * http://www.opensource.apple.com/apsl/ and read it before using this file. |
17 | * |
18 | * The Original Code and all software distributed under the License are |
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20 | * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, |
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23 | * Please see the License for the specific language governing rights and |
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25 | * |
26 | * @APPLE_OSREFERENCE_LICENSE_HEADER_END@ |
27 | */ |
28 | |
29 | #include <kern/locks_internal.h> |
30 | #include <kern/cpu_data.h> |
31 | #include <kern/machine.h> |
32 | #include <kern/mpsc_queue.h> |
33 | #include <kern/percpu.h> |
34 | #include <kern/sched.h> |
35 | #include <kern/smr.h> |
36 | #include <kern/smr_hash.h> |
37 | #include <kern/thread.h> |
38 | #include <kern/zalloc.h> |
39 | #include <machine/commpage.h> |
40 | #include <os/hash.h> |
41 | |
42 | |
43 | #pragma mark - SMR domains |
44 | |
45 | /* |
46 | * This SMR scheme is directly FreeBSD's "Global Unbounded Sequences". |
47 | * |
48 | * Major differences are: |
49 | * |
50 | * - only eager clocks are implemented (no lazy, no implicit) |
51 | * |
52 | * |
53 | * SMR clocks have 3 state machines interacting at any given time: |
54 | * |
55 | * 1. reader critical sections |
56 | * ~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
57 | * |
58 | * Each CPU can disable preemption and do this sequence: |
59 | * |
60 | * CPU::c_rd_seq = GLOBAL::c_wr_seq; |
61 | * |
62 | * < unfortunate place to receive a long IRQ > [I] |
63 | * |
64 | * os_atomic_thread_fence(seq_cst); [R1] |
65 | * |
66 | * { |
67 | * // critical section |
68 | * } |
69 | * |
70 | * os_atomic_store(&CPU::c_rd_seq, INVALID, release); [R2] |
71 | * |
72 | * |
73 | * |
74 | * 2. writer sequence advances |
75 | * ~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
76 | * |
77 | * Each writer can increment the global write sequence |
78 | * at any given time: |
79 | * |
80 | * os_atomic_add(&GLOBAL::c_wr_seq, SMR_SEQ_INC, release); [W] |
81 | * |
82 | * |
83 | * |
84 | * 3. synchronization sequence: poll/wait/scan |
85 | * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
86 | * |
87 | * This state machine synchronizes with the other two in order to decide |
88 | * if a given "goal" is in the past. Only the cases when the call |
89 | * is successful is interresting for barrier purposes, and we will focus |
90 | * on cases that do not take an early return for failures. |
91 | * |
92 | * a. __smr_poll: |
93 | * |
94 | * rd_seq = os_atomic_load(&GLOBAL::c_rd_seq, acquire); [S1] |
95 | * if (goal < rd_seq) SUCCESS. |
96 | * wr_seq = os_atomic_load(&GLOBAL::c_rd_seq, relaxed); |
97 | * |
98 | * b. __smr_scan |
99 | * |
100 | * os_atomic_thread_fence(seq_cst) [S2] |
101 | * |
102 | * observe the minimum CPU::c_rd_seq "min_rd_seq" |
103 | * value possible or rw_seq if no CPU was in a critical section. |
104 | * (possibly spinning until it satisfies "goal") |
105 | * |
106 | * c. __smr_rd_advance |
107 | * |
108 | * cur_rd_seq = load_exclusive(&GLOBAL::c_rd_seq); |
109 | * os_atomic_thread_fence(seq_cst); [S3] |
110 | * if (min_rd_seq > cur_rd_seq) { |
111 | * store_exlusive(&GLOBAL::c_rd_seq, min_rd_seq); |
112 | * } |
113 | * |
114 | * |
115 | * One sentence summary |
116 | * ~~~~~~~~~~~~~~~~~~~~ |
117 | * |
118 | * A simplistic one-sentence summary of the algorithm is that __smr_scan() |
119 | * works really hard to insert itself in the timeline of write sequences and |
120 | * observe a reasonnable bound for first safe-to-reclaim sequence, and |
121 | * issues [S3] to sequence everything around "c_rd_seq" (via [S3] -> [S1]): |
122 | * |
123 | * GLOBAL::c_rd_seq GLOBAL::c_wr_seq |
124 | * v v |
125 | * ──────────────────────┬────────────────┬───────────────────── |
126 | * ... safe to reclaim │ deferred │ future ... |
127 | * ──────────────────────┴────────────────┴───────────────────── |
128 | * |
129 | * |
130 | * Detailed explanation |
131 | * ~~~~~~~~~~~~~~~~~~~~ |
132 | * |
133 | * [W] -> [R1] establishes a "happens before" relationship between a given |
134 | * writer and this critical section. The loaded GLOBAL::c_wr_seq might |
135 | * however be stale with respect to the one [R1] really synchronizes with |
136 | * (see [I] explanation below). |
137 | * |
138 | * |
139 | * [R1] -> [S2] establishes a "happens before" relationship between all the |
140 | * active critical sections and the scanner. |
141 | * It lets us compute the oldest possible sequence pinned by an active |
142 | * critical section. |
143 | * |
144 | * |
145 | * [R2] -> [S3] establishes a "happens before" relationship between all the |
146 | * inactive critical sections and the scanner. |
147 | * |
148 | * |
149 | * [S3] -> [S1] is the typical expected fastpath: when the caller can decide |
150 | * that its goal is older than the last update an __smr_rd_advance() did. |
151 | * Note that [S3] doubles as an "[S1]" when two __smr_scan() race each other |
152 | * and one of them finishes last but observed a "worse" read sequence. |
153 | * |
154 | * |
155 | * [W], [S3] -> [S1] is the last crucial property: all updates to the global |
156 | * clock are totally ordered because they update the entire 128bit state |
157 | * every time with an RMW. This guarantees that __smr_poll() can't load |
158 | * an `rd_seq` that is younger than the `wr_seq` it loads next. |
159 | * |
160 | * |
161 | * [I] __smr_enter() also can be unfortunately delayed after observing |
162 | * a given write sequence and right before [R1] at [I]. |
163 | * |
164 | * However for a read sequence to have move past what __smr_enter() observed, |
165 | * it means another __smr_scan() didn't observe the store to CPU::c_rd_seq |
166 | * made by __smr_enter() and thought the section was inactive. |
167 | * |
168 | * This can only happen if the scan's [S2] was issued before the delayed |
169 | * __smr_enter() [R1] (during the [I] window). |
170 | * |
171 | * As a consequence the outcome of that scan can be accepted as the "real" |
172 | * write sequence __smr_enter() should have observed. |
173 | * |
174 | * |
175 | * Litmus tests |
176 | * ~~~~~~~~~~~~ |
177 | * |
178 | * This is the proof of [W] -> [R1] -> [S2] being established properly: |
179 | * - P0 sets a global and calls smr_synchronize() |
180 | * - P1 does smr_enter() and loads the global |
181 | * |
182 | * AArch64 MP |
183 | * { |
184 | * global = 0; |
185 | * wr_seq = 123; |
186 | * p1_rd_seq = 0; |
187 | * |
188 | * 0:x0 = global; 0:x1 = wr_seq; 0:x2 = p1_rd_seq; |
189 | * 1:x0 = global; 1:x1 = wr_seq; 1:x2 = p1_rd_seq; |
190 | * } |
191 | * P0 | P1 ; |
192 | * MOV X8, #2 | LDR X8, [X1] ; |
193 | * STR X8, [X0] | STR X8, [X2] ; |
194 | * LDADDL X8, X9, [X1] | DMB SY ; |
195 | * DMB SY | LDR X10, [X0] ; |
196 | * LDR X10, [X2] | ; |
197 | * exists (0:X10 = 0 /\ 1:X8 = 123 /\ 1:X10 = 0) |
198 | * |
199 | * |
200 | * This is the proof that deferred advances are also correct: |
201 | * - P0 sets a global and does a smr_deferred_advance() |
202 | * - P1 does an smr_synchronize() and reads the global |
203 | * |
204 | * AArch64 MP |
205 | * { |
206 | * global = 0; |
207 | * wr_seq = 123; |
208 | * |
209 | * 0:x0 = global; 0:x1 = wr_seq; 0:x2 = 2; |
210 | * 1:x0 = global; 1:x1 = wr_seq; 1:x2 = 2; |
211 | * } |
212 | * P0 | P1 ; |
213 | * STR X2, [X0] | LDADDL X2, X9, [X1] ; |
214 | * DMB SY | DMB SY ; |
215 | * LDR X9, [X1] | LDR X10, [X0] ; |
216 | * ADD X9, X9, X2 | ; |
217 | * exists (0:X9 = 125 /\ 1:X9 = 123 /\ 1:X10 = 0) |
218 | * |
219 | */ |
220 | |
221 | /*! |
222 | * @struct smr_worker |
223 | * |
224 | * @brief |
225 | * Structure tracking the per-cpu SMR workers state. |
226 | * |
227 | * @discussion |
228 | * This structure is system wide and global and is used to track |
229 | * the various active SMR domains at the granularity of a CPU. |
230 | * |
231 | * Each structure has an associated thread which is responsible |
232 | * for the forward progress the @c smr_call() and @c smr_barrier() |
233 | * interfaces. |
234 | * |
235 | * It also tracks all the active, non stalled, sleepable SMR sections. |
236 | */ |
237 | struct smr_worker { |
238 | /* |
239 | * The thread for this worker, |
240 | * and conveniency pointer to the processor it is bound to. |
241 | */ |
242 | struct thread *thread; |
243 | struct processor *processor; |
244 | |
245 | /* |
246 | * Thread binding/locking logic: |
247 | * |
248 | * If the worker thread is running on its canonical CPU, |
249 | * then locking to access the various SMR per-cpu data |
250 | * structures it is draining is just preemption disablement. |
251 | * |
252 | * However, if it is currently not bound to its canonical |
253 | * CPU because the CPU has been offlined or de-recommended, |
254 | * then a lock which serializes with the CPU going online |
255 | * again is being used. |
256 | */ |
257 | struct waitq waitq; |
258 | smr_cpu_reason_t detach_reason; |
259 | |
260 | #if CONFIG_QUIESCE_COUNTER |
261 | /* |
262 | * Currently active quiescent generation for this processor, |
263 | * and the last timestamp when a scan of all cores was performed. |
264 | */ |
265 | smr_seq_t rd_quiesce_seq; |
266 | #endif |
267 | |
268 | /* |
269 | * List of all the active sleepable sections that haven't |
270 | * been stalled. |
271 | */ |
272 | struct smrq_list_head sect_queue; |
273 | struct thread *sect_waiter; |
274 | |
275 | /* |
276 | * Queue of SMR domains with pending smr_call() |
277 | * callouts to drain. |
278 | * |
279 | * This uses an ageing strategy in order to amortize |
280 | * SMR clock updates: |
281 | * |
282 | * - the "old" queue have domains whose callbacks have |
283 | * a committed and aged sequence, |
284 | * - the "age" queue have domains whose callbacks have |
285 | * a commited but fresh sequence and need ageing, |
286 | * - the "cur" queue have domains whose callbacks have |
287 | * a sequence in the future and need for it to be committed. |
288 | */ |
289 | struct smr_pcpu *whead; |
290 | struct smr_pcpu **wold_tail; |
291 | struct smr_pcpu **wage_tail; |
292 | struct smr_pcpu **wcur_tail; |
293 | uint64_t drain_ctime; |
294 | |
295 | /* |
296 | * Queue of smr_barrier() calls in flight, |
297 | * that will be picked up by the worker thread |
298 | * to enqueue as smr_call() entries in their |
299 | * respective per-CPU data structures. |
300 | */ |
301 | struct mpsc_queue_head barrier_queue; |
302 | } __attribute__((aligned(64))); |
303 | |
304 | |
305 | typedef struct smr_pcpu { |
306 | /* |
307 | * CPU private cacheline. |
308 | * |
309 | * Nothing else than the CPU this state is made for, |
310 | * ever writes to this cacheline. |
311 | * |
312 | * It holds the epoch activity witness (rd_seq), and |
313 | * the local smr_call() queue, which is structured this way: |
314 | * |
315 | * head -> n1 -> n2 -> n3 -> n4 -> ... -> ni -> ... -> nN -> NULL |
316 | * ^ ^ ^ |
317 | * qold_tail -------------' | | |
318 | * qage_tail --------------------------' | |
319 | * qcur_tail ---------------------------------------------' |
320 | * |
321 | * - the "old" queue can be reclaimed once qold_seq is past, |
322 | * qold_seq is always a commited sequence. |
323 | * - the "age" queue can be reclaimed once qage_seq is past, |
324 | * qage_seq might not be commited yet. |
325 | * - the "cur" queue has an approximate size of qcur_size bytes, |
326 | * and a length of qcur_cnt callbacks. |
327 | */ |
328 | |
329 | smr_seq_t c_rd_seq; /* might have SMR_SEQ_SLEEPABLE set */ |
330 | |
331 | smr_node_t qhead; |
332 | |
333 | smr_seq_t qold_seq; |
334 | smr_node_t *qold_tail; |
335 | |
336 | smr_seq_t qage_seq; |
337 | smr_node_t *qage_tail; |
338 | |
339 | uint32_t qcur_size; |
340 | uint32_t qcur_cnt; |
341 | smr_node_t *qcur_tail; |
342 | |
343 | uint8_t __cacheline_sep[0]; |
344 | |
345 | /* |
346 | * Drain queue. |
347 | * |
348 | * This is used to drive smr_call() via the smr worker threads. |
349 | * If the SMR domain is not using smr_call() or smr_barrier(), |
350 | * this isn't used. |
351 | */ |
352 | struct smr *drain_smr; |
353 | struct smr_pcpu *drain_next; |
354 | uint16_t __check_cpu; |
355 | uint8_t __check_reason; |
356 | uint8_t __check_list; |
357 | |
358 | /* |
359 | * Stalled queue. |
360 | * |
361 | * Stalled sections are enqueued onto this queue by the scheduler |
362 | * when their thread blocks (see smr_mark_active_trackers_stalled()). |
363 | * |
364 | * If the SMR domain is not sleepable, then this isn't used. |
365 | * |
366 | * This list is protected by a lock. |
367 | * |
368 | * When there are stalled sections, stall_rd_seq contains |
369 | * the oldest active stalled sequence number. |
370 | * |
371 | * When threads want to expedite a stalled section, they set |
372 | * stall_waiter_goal to the sequence number they are waiting |
373 | * for and block via turnstile on the oldest stalled section. |
374 | */ |
375 | hw_lck_ticket_t stall_lock; |
376 | smr_seq_t stall_rd_seq; |
377 | smr_seq_t stall_waiter_goal; |
378 | struct smrq_tailq_head stall_queue; |
379 | struct turnstile *stall_ts; |
380 | } __attribute__((aligned(128))) * smr_pcpu_t; |
381 | |
382 | static_assert(offsetof(struct smr_pcpu, __cacheline_sep) == 64); |
383 | static_assert(sizeof(struct smr_pcpu) == 128); |
384 | |
385 | #define CPU_CHECKIN_MIN_INTERVAL_US 5000 /* 5ms */ |
386 | #define CPU_CHECKIN_MIN_INTERVAL_MAX_US USEC_PER_SEC /* 1s */ |
387 | static uint64_t cpu_checkin_min_interval; |
388 | static uint32_t cpu_checkin_min_interval_us; |
389 | |
390 | /*! the amount of memory pending retiring that causes a foreceful flush */ |
391 | #if XNU_TARGET_OS_OSX |
392 | static TUNABLE(vm_size_t, smr_call_size_cap, "smr_call_size_cap" , 256 << 10); |
393 | static TUNABLE(vm_size_t, smr_call_cnt_cap, "smr_call_cnt_cap" , 128); |
394 | #else |
395 | static TUNABLE(vm_size_t, smr_call_size_cap, "smr_call_size_cap" , 64 << 10); |
396 | static TUNABLE(vm_size_t, smr_call_cnt_cap, "smr_call_cnt_cap" , 32); |
397 | #endif |
398 | /* time __smr_wait_for_oncore busy spins before going the expensive route */ |
399 | static TUNABLE(uint32_t, smr_wait_spin_us, "smr_wait_spin_us" , 20); |
400 | |
401 | static LCK_GRP_DECLARE(smr_lock_grp, "smr" ); |
402 | static struct smr_worker PERCPU_DATA(smr_worker); |
403 | static struct smrq_tailq_head smr_domains = SMRQ_TAILQ_INITIALIZER(smr_domains); |
404 | |
405 | SMR_DEFINE_FLAGS(smr_system, "system" , SMR_NONE); |
406 | SMR_DEFINE_FLAGS(smr_system_sleepable, "system (sleepable)" , SMR_SLEEPABLE); |
407 | |
408 | |
409 | #pragma mark SMR domains: init & helpers |
410 | |
411 | #define SMR_PCPU_NOT_QUEUED ((struct smr_pcpu *)-1) |
412 | |
413 | __attribute__((always_inline, overloadable)) |
414 | static inline smr_pcpu_t |
415 | __smr_pcpu(smr_t smr, int cpu) |
416 | { |
417 | return &smr->smr_pcpu[cpu]; |
418 | } |
419 | |
420 | __attribute__((always_inline, overloadable)) |
421 | static inline smr_pcpu_t |
422 | __smr_pcpu(smr_t smr) |
423 | { |
424 | return __smr_pcpu(smr, cpu: cpu_number()); |
425 | } |
426 | |
427 | static inline bool |
428 | __smr_pcpu_queued(smr_pcpu_t pcpu) |
429 | { |
430 | return pcpu->drain_next != SMR_PCPU_NOT_QUEUED; |
431 | } |
432 | |
433 | static inline void |
434 | __smr_pcpu_set_not_queued(smr_pcpu_t pcpu) |
435 | { |
436 | pcpu->drain_next = SMR_PCPU_NOT_QUEUED; |
437 | } |
438 | |
439 | static inline void |
440 | __smr_pcpu_associate(smr_t smr, smr_pcpu_t pcpu) |
441 | { |
442 | zpercpu_foreach_cpu(cpu) { |
443 | pcpu[cpu].qold_tail = &pcpu[cpu].qhead; |
444 | pcpu[cpu].qage_tail = &pcpu[cpu].qhead; |
445 | pcpu[cpu].qcur_tail = &pcpu[cpu].qhead; |
446 | |
447 | pcpu[cpu].drain_smr = smr; |
448 | __smr_pcpu_set_not_queued(pcpu: &pcpu[cpu]); |
449 | hw_lck_ticket_init(&pcpu[cpu].stall_lock, &smr_lock_grp); |
450 | smrq_init(&pcpu[cpu].stall_queue); |
451 | } |
452 | |
453 | os_atomic_store(&smr->smr_pcpu, pcpu, release); |
454 | } |
455 | |
456 | static inline event64_t |
457 | __smrw_oncore_event(struct smr_worker *smrw) |
458 | { |
459 | return CAST_EVENT64_T(&smrw->sect_queue); |
460 | } |
461 | |
462 | static inline event64_t |
463 | __smrw_drain_event(struct smr_worker *smrw) |
464 | { |
465 | return CAST_EVENT64_T(&smrw->whead); |
466 | } |
467 | |
468 | static inline processor_t |
469 | __smrw_drain_bind_target(struct smr_worker *smrw) |
470 | { |
471 | return smrw->detach_reason ? PROCESSOR_NULL : smrw->processor; |
472 | } |
473 | |
474 | static inline void |
475 | __smrw_lock(struct smr_worker *smrw) |
476 | { |
477 | waitq_lock(wq: &smrw->waitq); |
478 | } |
479 | |
480 | static inline void |
481 | __smrw_unlock(struct smr_worker *smrw) |
482 | { |
483 | waitq_unlock(wq: &smrw->waitq); |
484 | } |
485 | |
486 | /*! |
487 | * @function __smrw_wakeup_and_unlock() |
488 | * |
489 | * @brief |
490 | * Wakes up (with binding) the SMR worker. |
491 | * |
492 | * @discussion |
493 | * Wakeup the worker thread and bind it to the proper processor |
494 | * as a side effect. |
495 | * |
496 | * This function must be called with interrupts disabled. |
497 | */ |
498 | static bool |
499 | __smrw_wakeup_and_unlock(struct smr_worker *smrw) |
500 | { |
501 | thread_t thread; |
502 | |
503 | assert(!ml_get_interrupts_enabled()); |
504 | |
505 | thread = waitq_wakeup64_identify_locked(waitq: &smrw->waitq, |
506 | wake_event: __smrw_drain_event(smrw), THREAD_AWAKENED, flags: WAITQ_UNLOCK); |
507 | |
508 | if (thread != THREAD_NULL) { |
509 | assert(thread == smrw->thread); |
510 | |
511 | waitq_resume_and_bind_identified_thread(waitq: &smrw->waitq, |
512 | thread, processor: __smrw_drain_bind_target(smrw), |
513 | THREAD_AWAKENED, flags: WAITQ_WAKEUP_DEFAULT); |
514 | } |
515 | |
516 | return thread != THREAD_NULL; |
517 | } |
518 | |
519 | static void |
520 | __smr_call_drain(smr_node_t head) |
521 | { |
522 | smr_node_t node; |
523 | |
524 | while ((node = head) != NULL) { |
525 | head = node->smrn_next; |
526 | node->smrn_next = NULL; |
527 | node->smrn_cb(node); |
528 | } |
529 | } |
530 | |
531 | __startup_func |
532 | void |
533 | __smr_domain_init(smr_t smr) |
534 | { |
535 | smr_pcpu_t pcpu; |
536 | vm_size_t size; |
537 | |
538 | if (startup_phase < STARTUP_SUB_TUNABLES) { |
539 | smr_seq_t *rd_seqp = &smr->smr_early; |
540 | |
541 | /* |
542 | * This is a big cheat, but before the EARLY_BOOT phase, |
543 | * all smr_* APIs that would access past the rd_seq |
544 | * will early return. |
545 | */ |
546 | pcpu = __container_of(rd_seqp, struct smr_pcpu, c_rd_seq); |
547 | smr->smr_pcpu = pcpu - cpu_number(); |
548 | assert(&__smr_pcpu(smr)->c_rd_seq == &smr->smr_early); |
549 | } else { |
550 | size = zpercpu_count() * sizeof(struct smr_pcpu); |
551 | pcpu = zalloc_permanent(size, ZALIGN(struct smr_pcpu)); |
552 | |
553 | __smr_pcpu_associate(smr, pcpu); |
554 | } |
555 | } |
556 | |
557 | smr_t |
558 | smr_domain_create(smr_flags_t flags, const char *name) |
559 | { |
560 | smr_pcpu_t pcpu; |
561 | smr_t smr; |
562 | |
563 | smr = kalloc_type(struct smr, Z_WAITOK | Z_ZERO | Z_NOFAIL); |
564 | pcpu = kalloc_type(struct smr_pcpu, zpercpu_count(), |
565 | Z_WAITOK | Z_ZERO | Z_NOFAIL); |
566 | |
567 | smr->smr_clock.s_rd_seq = SMR_SEQ_INIT; |
568 | smr->smr_clock.s_wr_seq = SMR_SEQ_INIT; |
569 | smr->smr_flags = flags; |
570 | static_assert(sizeof(struct smr) == |
571 | offsetof(struct smr, smr_name) + SMR_NAME_MAX); |
572 | strlcpy(dst: smr->smr_name, src: name, n: sizeof(smr->smr_name)); |
573 | |
574 | __smr_pcpu_associate(smr, pcpu); |
575 | |
576 | return smr; |
577 | } |
578 | |
579 | void |
580 | smr_domain_free(smr_t smr) |
581 | { |
582 | smr_barrier(smr); |
583 | |
584 | zpercpu_foreach_cpu(cpu) { |
585 | smr_pcpu_t pcpu = __smr_pcpu(smr, cpu); |
586 | |
587 | assert(pcpu->qhead == NULL); |
588 | hw_lck_ticket_destroy(&pcpu->stall_lock, &smr_lock_grp); |
589 | } |
590 | |
591 | kfree_type(struct smr_pcpu, zpercpu_count(), smr->smr_pcpu); |
592 | kfree_type(struct smr, smr); |
593 | } |
594 | |
595 | |
596 | #pragma mark SMR domains: enter / leave |
597 | |
598 | bool |
599 | smr_entered(smr_t smr) |
600 | { |
601 | thread_t self = current_thread(); |
602 | smr_tracker_t t; |
603 | |
604 | if (lock_preemption_level_for_thread(self) && |
605 | __smr_pcpu(smr)->c_rd_seq != SMR_SEQ_INVALID) { |
606 | return true; |
607 | } |
608 | |
609 | if (smr->smr_flags & SMR_SLEEPABLE) { |
610 | smrq_serialized_foreach(t, &self->smr_stack, smrt_stack) { |
611 | if (t->smrt_domain == smr) { |
612 | return true; |
613 | } |
614 | } |
615 | } |
616 | |
617 | return false; |
618 | } |
619 | |
620 | __attribute__((always_inline)) |
621 | bool |
622 | smr_entered_cpu_noblock(smr_t smr, int cpu) |
623 | { |
624 | assert((smr->smr_flags & SMR_SLEEPABLE) == 0); |
625 | return __smr_pcpu(smr, cpu)->c_rd_seq != SMR_SEQ_INVALID; |
626 | } |
627 | |
628 | __attribute__((always_inline)) |
629 | static smr_seq_t |
630 | __smr_enter(smr_t smr, smr_pcpu_t pcpu, smr_seq_t sleepable) |
631 | { |
632 | smr_seq_t s_wr_seq; |
633 | smr_seq_t old_seq; |
634 | |
635 | assert(!ml_at_interrupt_context()); |
636 | |
637 | /* |
638 | * It is possible to have a long delay between loading the s_wr_seq |
639 | * and storing it to the percpu copy of it. |
640 | * |
641 | * It is unlikely but possible by that time the s_rd_seq advances |
642 | * ahead of what we will store. This however is still safe |
643 | * and handled in __smr_scan(). |
644 | * |
645 | * On Intel, to achieve the ordering we want, we could use a store |
646 | * followed by an mfence, or any RMW (XCHG, XADD, CMPXCHG, ...). |
647 | * XADD is just the fastest instruction of the alternatives, |
648 | * but it will only ever add to '0'. |
649 | */ |
650 | s_wr_seq = os_atomic_load(&smr->smr_clock.s_wr_seq, relaxed); |
651 | #if __x86_64__ |
652 | /* [R1] */ |
653 | old_seq = os_atomic_add_orig(&pcpu->c_rd_seq, s_wr_seq | sleepable, seq_cst); |
654 | #else |
655 | old_seq = pcpu->c_rd_seq; |
656 | os_atomic_store(&pcpu->c_rd_seq, s_wr_seq | sleepable, relaxed); |
657 | os_atomic_thread_fence(seq_cst); /* [R1] */ |
658 | #endif |
659 | assert(old_seq == SMR_SEQ_INVALID); |
660 | |
661 | return s_wr_seq; |
662 | } |
663 | |
664 | __attribute__((always_inline)) |
665 | static void |
666 | __smr_leave(smr_pcpu_t pcpu) |
667 | { |
668 | assert(!ml_at_interrupt_context()); |
669 | /* [R2] */ |
670 | os_atomic_store(&pcpu->c_rd_seq, SMR_SEQ_INVALID, release); |
671 | } |
672 | |
673 | __attribute__((always_inline)) |
674 | void |
675 | smr_enter(smr_t smr) |
676 | { |
677 | disable_preemption(); |
678 | __smr_enter(smr, pcpu: __smr_pcpu(smr), sleepable: 0); |
679 | } |
680 | |
681 | __attribute__((always_inline)) |
682 | void |
683 | smr_leave(smr_t smr) |
684 | { |
685 | __smr_leave(pcpu: __smr_pcpu(smr)); |
686 | enable_preemption(); |
687 | } |
688 | |
689 | void |
690 | smr_enter_sleepable(smr_t smr, smr_tracker_t tracker) |
691 | { |
692 | thread_t self = current_thread(); |
693 | struct smr_worker *smrw; |
694 | smr_pcpu_t pcpu; |
695 | |
696 | assert(smr->smr_flags & SMR_SLEEPABLE); |
697 | |
698 | lock_disable_preemption_for_thread(self); |
699 | lck_rw_lock_count_inc(thread: self, lock: smr); |
700 | |
701 | pcpu = __smr_pcpu(smr); |
702 | smrw = PERCPU_GET(smr_worker); |
703 | |
704 | tracker->smrt_domain = smr; |
705 | tracker->smrt_seq = __smr_enter(smr, pcpu, SMR_SEQ_SLEEPABLE); |
706 | smrq_serialized_insert_head_relaxed(&smrw->sect_queue, &tracker->smrt_link); |
707 | smrq_serialized_insert_head_relaxed(&self->smr_stack, &tracker->smrt_stack); |
708 | tracker->smrt_ctid = 0; |
709 | tracker->smrt_cpu = -1; |
710 | |
711 | lock_enable_preemption(); |
712 | } |
713 | |
714 | __attribute__((always_inline)) |
715 | static void |
716 | __smr_wake_oncore_sleepers(struct smr_worker *smrw) |
717 | { |
718 | /* |
719 | * prevent reordering of making the list empty and checking for waiters. |
720 | */ |
721 | if (__improbable(os_atomic_load(&smrw->sect_waiter, compiler_acq_rel))) { |
722 | if (smrq_empty(&smrw->sect_queue)) { |
723 | os_atomic_store(&smrw->sect_waiter, NULL, relaxed); |
724 | waitq_wakeup64_all(waitq: &smrw->waitq, |
725 | wake_event: __smrw_oncore_event(smrw), THREAD_AWAKENED, |
726 | flags: WAITQ_WAKEUP_DEFAULT); |
727 | } |
728 | } |
729 | } |
730 | |
731 | void |
732 | smr_ack_ipi(void) |
733 | { |
734 | /* |
735 | * see __smr_wait_for_oncore(): if at the time of the IPI ack |
736 | * the list is empty and there is still a waiter, wake it up. |
737 | * |
738 | * If the queue is not empty, then when smr_leave_sleepable() |
739 | * runs it can't possibly fail to observe smrw->sect_waiter |
740 | * being non NULL and will do the wakeup then. |
741 | */ |
742 | __smr_wake_oncore_sleepers(PERCPU_GET(smr_worker)); |
743 | } |
744 | |
745 | void |
746 | smr_mark_active_trackers_stalled(thread_t self) |
747 | { |
748 | struct smr_worker *smrw = PERCPU_GET(smr_worker); |
749 | int cpu = cpu_number(); |
750 | smr_tracker_t t; |
751 | |
752 | /* called at splsched */ |
753 | |
754 | smrq_serialized_foreach_safe(t, &smrw->sect_queue, smrt_link) { |
755 | smr_t smr = t->smrt_domain; |
756 | smr_pcpu_t pcpu; |
757 | |
758 | pcpu = __smr_pcpu(smr, cpu); |
759 | |
760 | t->smrt_ctid = self->ctid; |
761 | t->smrt_cpu = cpu; |
762 | |
763 | hw_lck_ticket_lock_nopreempt(&pcpu->stall_lock, &smr_lock_grp); |
764 | |
765 | /* |
766 | * Transfer the section to the stalled queue, |
767 | * and _then_ leave the regular one. |
768 | * |
769 | * A store-release is sufficient to order these stores, |
770 | * and guarantee that __smr_scan() can't fail to observe |
771 | * both the @c rd_seq and @c stall_rd_seq during a transfer |
772 | * of a stalled section that was active when it started. |
773 | */ |
774 | if (smrq_empty(&pcpu->stall_queue)) { |
775 | os_atomic_store(&pcpu->stall_rd_seq, t->smrt_seq, relaxed); |
776 | } |
777 | os_atomic_store(&pcpu->c_rd_seq, SMR_SEQ_INVALID, release); |
778 | |
779 | smrq_serialized_insert_tail_relaxed(&pcpu->stall_queue, &t->smrt_link); |
780 | |
781 | hw_lck_ticket_unlock_nopreempt(tlock: &pcpu->stall_lock); |
782 | } |
783 | |
784 | smrq_init(&smrw->sect_queue); |
785 | |
786 | __smr_wake_oncore_sleepers(smrw); |
787 | } |
788 | |
789 | |
790 | __attribute__((noinline)) |
791 | static void |
792 | __smr_leave_stalled(smr_t smr, smr_tracker_t tracker, thread_t self) |
793 | { |
794 | smr_seq_t new_stall_seq = SMR_SEQ_INVALID; |
795 | smr_tracker_t first = NULL; |
796 | smr_pcpu_t pcpu; |
797 | bool progress; |
798 | |
799 | pcpu = __smr_pcpu(smr, cpu: tracker->smrt_cpu); |
800 | |
801 | hw_lck_ticket_lock_nopreempt(&pcpu->stall_lock, &smr_lock_grp); |
802 | |
803 | progress = smrq_serialized_first(&pcpu->stall_queue, |
804 | struct smr_tracker, smrt_link) == tracker; |
805 | |
806 | smrq_serialized_remove(&self->smr_stack, &tracker->smrt_stack); |
807 | smrq_serialized_remove(&pcpu->stall_queue, &tracker->smrt_link); |
808 | bzero(s: tracker, n: sizeof(*tracker)); |
809 | |
810 | if (progress) { |
811 | if (!smrq_empty(&pcpu->stall_queue)) { |
812 | first = smrq_serialized_first(&pcpu->stall_queue, |
813 | struct smr_tracker, smrt_link); |
814 | new_stall_seq = first->smrt_seq; |
815 | __builtin_assume(new_stall_seq != SMR_SEQ_INVALID); |
816 | assert(SMR_SEQ_CMP(pcpu->stall_rd_seq, <=, new_stall_seq)); |
817 | } |
818 | |
819 | os_atomic_store(&pcpu->stall_rd_seq, new_stall_seq, release); |
820 | |
821 | progress = pcpu->stall_waiter_goal != SMR_SEQ_INVALID; |
822 | } |
823 | |
824 | if (progress) { |
825 | struct turnstile *ts; |
826 | |
827 | ts = turnstile_prepare(proprietor: (uintptr_t)pcpu, tstore: &pcpu->stall_ts, |
828 | TURNSTILE_NULL, type: TURNSTILE_KERNEL_MUTEX); |
829 | |
830 | if (new_stall_seq == SMR_SEQ_INVALID || |
831 | SMR_SEQ_CMP(pcpu->stall_waiter_goal, <=, new_stall_seq)) { |
832 | pcpu->stall_waiter_goal = SMR_SEQ_INVALID; |
833 | waitq_wakeup64_all(waitq: &ts->ts_waitq, CAST_EVENT64_T(pcpu), |
834 | THREAD_AWAKENED, flags: WAITQ_UPDATE_INHERITOR); |
835 | } else { |
836 | turnstile_update_inheritor(turnstile: ts, new_inheritor: ctid_get_thread(ctid: first->smrt_ctid), |
837 | flags: TURNSTILE_IMMEDIATE_UPDATE | TURNSTILE_INHERITOR_THREAD); |
838 | } |
839 | |
840 | turnstile_update_inheritor_complete(turnstile: ts, flags: TURNSTILE_INTERLOCK_HELD); |
841 | |
842 | turnstile_complete(proprietor: (uintptr_t)pcpu, tstore: &pcpu->stall_ts, |
843 | NULL, type: TURNSTILE_KERNEL_MUTEX); |
844 | } |
845 | |
846 | /* reenables preemption disabled in smr_leave_sleepable() */ |
847 | hw_lck_ticket_unlock(tlock: &pcpu->stall_lock); |
848 | |
849 | turnstile_cleanup(); |
850 | } |
851 | |
852 | void |
853 | smr_leave_sleepable(smr_t smr, smr_tracker_t tracker) |
854 | { |
855 | struct smr_worker *smrw; |
856 | thread_t self = current_thread(); |
857 | |
858 | assert(tracker->smrt_seq != SMR_SEQ_INVALID); |
859 | assert(smr->smr_flags & SMR_SLEEPABLE); |
860 | |
861 | lock_disable_preemption_for_thread(self); |
862 | |
863 | lck_rw_lock_count_dec(thread: self, lock: smr); |
864 | |
865 | if (__improbable(tracker->smrt_cpu != -1)) { |
866 | return __smr_leave_stalled(smr, tracker, self); |
867 | } |
868 | |
869 | __smr_leave(pcpu: __smr_pcpu(smr)); |
870 | |
871 | smrw = PERCPU_GET(smr_worker); |
872 | smrq_serialized_remove(&self->smr_stack, &tracker->smrt_stack); |
873 | smrq_serialized_remove(&smrw->sect_queue, &tracker->smrt_link); |
874 | bzero(s: tracker, n: sizeof(*tracker)); |
875 | |
876 | __smr_wake_oncore_sleepers(PERCPU_GET(smr_worker)); |
877 | |
878 | lock_enable_preemption(); |
879 | } |
880 | |
881 | |
882 | #pragma mark SMR domains: advance, wait, poll, synchronize |
883 | |
884 | static inline smr_seq_t |
885 | __smr_wr_advance(smr_t smr) |
886 | { |
887 | /* [W] */ |
888 | return os_atomic_add(&smr->smr_clock.s_wr_seq, SMR_SEQ_INC, release); |
889 | } |
890 | |
891 | static inline bool |
892 | __smr_rd_advance(smr_t smr, smr_seq_t goal, smr_seq_t rd_seq) |
893 | { |
894 | smr_seq_t o_seq; |
895 | |
896 | os_atomic_thread_fence(seq_cst); /* [S3] */ |
897 | |
898 | os_atomic_rmw_loop(&smr->smr_clock.s_rd_seq, o_seq, rd_seq, relaxed, { |
899 | if (SMR_SEQ_CMP(rd_seq, <=, o_seq)) { |
900 | rd_seq = o_seq; |
901 | os_atomic_rmw_loop_give_up(break); |
902 | } |
903 | }); |
904 | |
905 | return SMR_SEQ_CMP(goal, <=, rd_seq); |
906 | } |
907 | |
908 | __attribute__((noinline)) |
909 | static smr_seq_t |
910 | __smr_wait_for_stalled(smr_pcpu_t pcpu, smr_seq_t goal) |
911 | { |
912 | struct turnstile *ts; |
913 | thread_t inheritor; |
914 | wait_result_t wr; |
915 | smr_seq_t stall_rd_seq; |
916 | |
917 | hw_lck_ticket_lock(&pcpu->stall_lock, &smr_lock_grp); |
918 | |
919 | stall_rd_seq = pcpu->stall_rd_seq; |
920 | if (stall_rd_seq == SMR_SEQ_INVALID || |
921 | SMR_SEQ_CMP(goal, <=, stall_rd_seq)) { |
922 | hw_lck_ticket_unlock(tlock: &pcpu->stall_lock); |
923 | return stall_rd_seq; |
924 | } |
925 | |
926 | if (pcpu->stall_waiter_goal == SMR_SEQ_INVALID || |
927 | SMR_SEQ_CMP(goal, <, pcpu->stall_waiter_goal)) { |
928 | pcpu->stall_waiter_goal = goal; |
929 | } |
930 | |
931 | inheritor = ctid_get_thread(smrq_serialized_first(&pcpu->stall_queue, |
932 | struct smr_tracker, smrt_link)->smrt_ctid); |
933 | |
934 | ts = turnstile_prepare(proprietor: (uintptr_t)pcpu, tstore: &pcpu->stall_ts, |
935 | TURNSTILE_NULL, type: TURNSTILE_KERNEL_MUTEX); |
936 | |
937 | turnstile_update_inheritor(turnstile: ts, new_inheritor: inheritor, |
938 | flags: TURNSTILE_DELAYED_UPDATE | TURNSTILE_INHERITOR_THREAD); |
939 | wr = waitq_assert_wait64(waitq: &ts->ts_waitq, CAST_EVENT64_T(pcpu), |
940 | THREAD_UNINT, TIMEOUT_WAIT_FOREVER); |
941 | turnstile_update_inheritor_complete(turnstile: ts, flags: TURNSTILE_INTERLOCK_HELD); |
942 | |
943 | if (wr == THREAD_WAITING) { |
944 | hw_lck_ticket_unlock(tlock: &pcpu->stall_lock); |
945 | thread_block(THREAD_CONTINUE_NULL); |
946 | hw_lck_ticket_lock(&pcpu->stall_lock, &smr_lock_grp); |
947 | } |
948 | |
949 | turnstile_complete(proprietor: (uintptr_t)pcpu, tstore: &pcpu->stall_ts, |
950 | NULL, type: TURNSTILE_KERNEL_MUTEX); |
951 | |
952 | stall_rd_seq = pcpu->stall_rd_seq; |
953 | hw_lck_ticket_unlock(tlock: &pcpu->stall_lock); |
954 | |
955 | turnstile_cleanup(); |
956 | |
957 | return stall_rd_seq; |
958 | } |
959 | |
960 | __attribute__((noinline)) |
961 | static smr_seq_t |
962 | __smr_wait_for_oncore(smr_pcpu_t pcpu, smr_seq_t goal, uint32_t cpu) |
963 | { |
964 | thread_t self = current_thread(); |
965 | struct smr_worker *smrw; |
966 | uint64_t deadline = 0; |
967 | vm_offset_t base; |
968 | smr_seq_t rd_seq; |
969 | |
970 | /* |
971 | * We are waiting for a currently active SMR section. |
972 | * Start spin-waiting for it for a bit. |
973 | */ |
974 | for (;;) { |
975 | if (hw_spin_wait_until(&pcpu->c_rd_seq, rd_seq, |
976 | rd_seq == SMR_SEQ_INVALID || SMR_SEQ_CMP(goal, <=, rd_seq))) { |
977 | return rd_seq; |
978 | } |
979 | |
980 | if (deadline == 0) { |
981 | clock_interval_to_deadline(interval: smr_wait_spin_us, |
982 | NSEC_PER_USEC, result: &deadline); |
983 | } else if (mach_absolute_time() > deadline) { |
984 | break; |
985 | } |
986 | } |
987 | |
988 | /* |
989 | * This section is being active for a while, |
990 | * we need to move to a more passive way of waiting. |
991 | * |
992 | * We post ourselves on the remote processor tracking head, |
993 | * to denote we need a thread_wakeup() when the tracker head clears, |
994 | * then send an IPI which will have 2 possible outcomes: |
995 | * |
996 | * 1. when smr_ack_ipi() runs, the queue is already cleared, |
997 | * and we will be woken up immediately. |
998 | * |
999 | * 2. when smr_ack_ipi() runs, the queue isn't cleared, |
1000 | * then it does nothing, but there is a guarantee that |
1001 | * when the queue clears, the remote core will observe |
1002 | * that there is a waiter, and thread_wakeup() will be |
1003 | * called then. |
1004 | * |
1005 | * In order to avoid to actually wait, we do spin some more, |
1006 | * hoping for the remote sequence to change. |
1007 | */ |
1008 | base = other_percpu_base(cpu_number: cpu); |
1009 | smrw = PERCPU_GET_WITH_BASE(base, smr_worker); |
1010 | |
1011 | waitq_assert_wait64(waitq: &smrw->waitq, wait_event: __smrw_oncore_event(smrw), |
1012 | THREAD_UNINT, TIMEOUT_WAIT_FOREVER); |
1013 | |
1014 | if (lock_cmpxchg(&smrw->sect_waiter, NULL, self, relaxed)) { |
1015 | /* |
1016 | * only really send the IPI if we're first, |
1017 | * to avoid IPI storms in case of a pile-up |
1018 | * of smr_synchronize() calls stalled on the same guy. |
1019 | */ |
1020 | cause_ast_check(PERCPU_GET_WITH_BASE(base, processor)); |
1021 | } |
1022 | |
1023 | if (hw_spin_wait_until(&pcpu->c_rd_seq, rd_seq, |
1024 | rd_seq == SMR_SEQ_INVALID || SMR_SEQ_CMP(goal, <=, rd_seq))) { |
1025 | clear_wait(thread: self, THREAD_AWAKENED); |
1026 | return rd_seq; |
1027 | } |
1028 | |
1029 | thread_block(THREAD_CONTINUE_NULL); |
1030 | |
1031 | return os_atomic_load(&pcpu->c_rd_seq, relaxed); |
1032 | } |
1033 | |
1034 | __attribute__((noinline)) |
1035 | static bool |
1036 | __smr_scan(smr_t smr, smr_seq_t goal, smr_clock_t clk, bool wait) |
1037 | { |
1038 | smr_delta_t delta; |
1039 | smr_seq_t rd_seq; |
1040 | |
1041 | if (__improbable(startup_phase < STARTUP_SUB_EARLY_BOOT)) { |
1042 | return true; |
1043 | } |
1044 | |
1045 | /* |
1046 | * Validate that the goal is sane. |
1047 | */ |
1048 | delta = SMR_SEQ_DELTA(goal, clk.s_wr_seq); |
1049 | if (delta == SMR_SEQ_INC) { |
1050 | /* |
1051 | * This SMR clock uses deferred advance, |
1052 | * and the goal is one inc in the future. |
1053 | * |
1054 | * If we can wait, then commit the sequence number, |
1055 | * else we can't possibly succeed. |
1056 | * |
1057 | * Doing a commit here rather than an advance |
1058 | * gives the hardware a chance to abort the |
1059 | * transaction early in case of high contention |
1060 | * compared to an unconditional advance. |
1061 | */ |
1062 | if (!wait) { |
1063 | return false; |
1064 | } |
1065 | if (lock_cmpxchgv(&smr->smr_clock.s_wr_seq, |
1066 | clk.s_wr_seq, goal, &clk.s_wr_seq, relaxed)) { |
1067 | clk.s_wr_seq = goal; |
1068 | } |
1069 | } else if (delta > 0) { |
1070 | /* |
1071 | * Invalid goal: the caller held on it for too long, |
1072 | * and integers wrapped. |
1073 | */ |
1074 | return true; |
1075 | } |
1076 | |
1077 | os_atomic_thread_fence(seq_cst); /* [S2] */ |
1078 | |
1079 | /* |
1080 | * The read sequence can be no larger than the write sequence |
1081 | * at the start of the poll. |
1082 | * |
1083 | * We know that on entry: |
1084 | * |
1085 | * s_rd_seq < goal <= s_wr_seq |
1086 | * |
1087 | * The correctness of this algorithm relies on the fact that |
1088 | * the SMR domain [s_rd_seq, s_wr_seq) can't possibly move |
1089 | * by more than roughly (ULONG_MAX / 2) while __smr_scan() |
1090 | * is running, otherwise the "rd_seq" we try to scan for |
1091 | * might appear larger than s_rd_seq spuriously and we'd |
1092 | * __smr_rd_advance() incorrectly. |
1093 | * |
1094 | * This is guaranteed by the fact that this represents |
1095 | * advancing 2^62 times. At one advance every nanosecond, |
1096 | * it takes more than a century, which makes it possible |
1097 | * to call smr_wait() or smr_poll() with preemption enabled. |
1098 | */ |
1099 | rd_seq = clk.s_wr_seq; |
1100 | |
1101 | zpercpu_foreach_cpu(cpu) { |
1102 | smr_pcpu_t pcpu = __smr_pcpu(smr, cpu); |
1103 | smr_seq_t seq = os_atomic_load(&pcpu->c_rd_seq, relaxed); |
1104 | |
1105 | while (seq != SMR_SEQ_INVALID) { |
1106 | /* |
1107 | * Resolve the race documented in __smr_enter(). |
1108 | * |
1109 | * The CPU has loaded a stale s_wr_seq, and s_rd_seq |
1110 | * moved past this stale value. |
1111 | * |
1112 | * Its critical section is however properly serialized, |
1113 | * but we can't know what the "correct" s_wr_seq it |
1114 | * could have observed was. We have to assume `s_rd_seq` |
1115 | * to prevent it from advancing. |
1116 | */ |
1117 | if (SMR_SEQ_CMP(seq, <, clk.s_rd_seq)) { |
1118 | seq = clk.s_rd_seq; |
1119 | } |
1120 | |
1121 | if (!wait || SMR_SEQ_CMP(goal, <=, seq)) { |
1122 | seq &= ~SMR_SEQ_SLEEPABLE; |
1123 | break; |
1124 | } |
1125 | |
1126 | if (seq & SMR_SEQ_SLEEPABLE) { |
1127 | seq = __smr_wait_for_oncore(pcpu, goal, cpu); |
1128 | } else { |
1129 | disable_preemption(); |
1130 | seq = hw_wait_while_equals_long(&pcpu->c_rd_seq, seq); |
1131 | enable_preemption(); |
1132 | } |
1133 | } |
1134 | |
1135 | if (seq != SMR_SEQ_INVALID && SMR_SEQ_CMP(seq, <, rd_seq)) { |
1136 | rd_seq = seq; |
1137 | } |
1138 | } |
1139 | |
1140 | if (smr->smr_flags & SMR_SLEEPABLE) { |
1141 | /* |
1142 | * Order observation of stalled sections, |
1143 | * see smr_mark_active_trackers_stalled(). |
1144 | */ |
1145 | os_atomic_thread_fence(seq_cst); |
1146 | |
1147 | zpercpu_foreach_cpu(cpu) { |
1148 | smr_pcpu_t pcpu = __smr_pcpu(smr, cpu); |
1149 | smr_seq_t seq = os_atomic_load(&pcpu->stall_rd_seq, relaxed); |
1150 | |
1151 | while (seq != SMR_SEQ_INVALID) { |
1152 | if (SMR_SEQ_CMP(seq, <, clk.s_rd_seq)) { |
1153 | seq = clk.s_rd_seq; |
1154 | } |
1155 | |
1156 | if (!wait || SMR_SEQ_CMP(goal, <=, seq)) { |
1157 | seq &= ~SMR_SEQ_SLEEPABLE; |
1158 | break; |
1159 | } |
1160 | |
1161 | seq = __smr_wait_for_stalled(pcpu, goal); |
1162 | } |
1163 | |
1164 | if (seq != SMR_SEQ_INVALID && SMR_SEQ_CMP(seq, <, rd_seq)) { |
1165 | rd_seq = seq; |
1166 | } |
1167 | } |
1168 | } |
1169 | |
1170 | /* |
1171 | * Advance the rd_seq as long as we observed a more recent value. |
1172 | */ |
1173 | return __smr_rd_advance(smr, goal, rd_seq); |
1174 | } |
1175 | |
1176 | static inline bool |
1177 | __smr_poll(smr_t smr, smr_seq_t goal, bool wait) |
1178 | { |
1179 | smr_clock_t clk; |
1180 | |
1181 | /* |
1182 | * Load both the s_rd_seq and s_wr_seq in the right order so that we |
1183 | * can't observe a s_rd_seq older than s_wr_seq. |
1184 | */ |
1185 | |
1186 | /* [S1] */ |
1187 | clk.s_rd_seq = os_atomic_load(&smr->smr_clock.s_rd_seq, acquire); |
1188 | |
1189 | /* |
1190 | * We expect this to be typical: the goal has already been observed. |
1191 | */ |
1192 | if (__probable(SMR_SEQ_CMP(goal, <=, clk.s_rd_seq))) { |
1193 | return true; |
1194 | } |
1195 | |
1196 | clk.s_wr_seq = os_atomic_load(&smr->smr_clock.s_wr_seq, relaxed); |
1197 | |
1198 | return __smr_scan(smr, goal, clk, wait); |
1199 | } |
1200 | |
1201 | smr_seq_t |
1202 | smr_advance(smr_t smr) |
1203 | { |
1204 | smr_clock_t clk; |
1205 | |
1206 | assert(!smr_entered(smr)); |
1207 | |
1208 | /* |
1209 | * We assume that there will at least be a successful __smr_poll |
1210 | * call every 2^60 calls to smr_advance() or so, so we do not need |
1211 | * to check if [s_rd_seq, s_wr_seq) is growing too wide. |
1212 | */ |
1213 | static_assert(sizeof(clk.s_wr_seq) == 8); |
1214 | return __smr_wr_advance(smr); |
1215 | } |
1216 | |
1217 | smr_seq_t |
1218 | smr_deferred_advance(smr_t smr) |
1219 | { |
1220 | os_atomic_thread_fence(seq_cst); |
1221 | return SMR_SEQ_INC + os_atomic_load(&smr->smr_clock.s_wr_seq, relaxed); |
1222 | } |
1223 | |
1224 | void |
1225 | smr_deferred_advance_commit(smr_t smr, smr_seq_t seq) |
1226 | { |
1227 | /* |
1228 | * no barrier needed: smr_deferred_advance() had one already. |
1229 | * no failure handling: it means someone updated the clock already! |
1230 | * lock_cmpxchg: so that we pre-test for architectures needing it. |
1231 | */ |
1232 | assert(seq != SMR_SEQ_INVALID); |
1233 | lock_cmpxchg(&smr->smr_clock.s_wr_seq, seq - SMR_SEQ_INC, seq, relaxed); |
1234 | } |
1235 | |
1236 | bool |
1237 | smr_poll(smr_t smr, smr_seq_t goal) |
1238 | { |
1239 | assert(!smr_entered(smr) && goal != SMR_SEQ_INVALID); |
1240 | return __smr_poll(smr, goal, false); |
1241 | } |
1242 | |
1243 | void |
1244 | smr_wait(smr_t smr, smr_seq_t goal) |
1245 | { |
1246 | assert(!smr_entered(smr) && goal != SMR_SEQ_INVALID); |
1247 | if (smr->smr_flags & SMR_SLEEPABLE) { |
1248 | assert(get_preemption_level() == 0); |
1249 | } |
1250 | (void)__smr_poll(smr, goal, true); |
1251 | } |
1252 | |
1253 | void |
1254 | smr_synchronize(smr_t smr) |
1255 | { |
1256 | smr_clock_t clk; |
1257 | |
1258 | assert(!smr_entered(smr)); |
1259 | assert(!ml_at_interrupt_context()); |
1260 | if (smr->smr_flags & SMR_SLEEPABLE) { |
1261 | assert(get_preemption_level() == 0); |
1262 | } |
1263 | |
1264 | /* |
1265 | * Similar to __smr_poll() but also does a deferred advance which |
1266 | * __smr_scan will commit. |
1267 | */ |
1268 | |
1269 | clk.s_rd_seq = os_atomic_load(&smr->smr_clock.s_rd_seq, relaxed); |
1270 | os_atomic_thread_fence(seq_cst); |
1271 | clk.s_wr_seq = os_atomic_load(&smr->smr_clock.s_wr_seq, relaxed); |
1272 | |
1273 | (void)__smr_scan(smr, goal: clk.s_wr_seq + SMR_SEQ_INC, clk, true); |
1274 | } |
1275 | |
1276 | |
1277 | #pragma mark SMR domains: smr_call & smr_barrier |
1278 | |
1279 | /*! |
1280 | * @struct smr_barrier_ctx |
1281 | * |
1282 | * @brief |
1283 | * Data structure to track the completion of an smr_barrier() call. |
1284 | */ |
1285 | struct smr_barrier_ctx { |
1286 | struct smr *smrb_domain; |
1287 | struct thread *smrb_waiter; |
1288 | uint32_t smrb_pending; |
1289 | uint32_t smrb_count; |
1290 | }; |
1291 | |
1292 | /*! |
1293 | * @struct smr_barrier_job |
1294 | * |
1295 | * @brief |
1296 | * Data structure used to track completion of smr_barrier() calls. |
1297 | */ |
1298 | struct smr_barrier_job { |
1299 | struct smr_barrier_ctx *smrj_context; |
1300 | union { |
1301 | struct smr_node smrj_node; |
1302 | struct mpsc_queue_chain smrj_link; |
1303 | }; |
1304 | }; |
1305 | |
1306 | #define SMR_BARRIER_SIZE 24 |
1307 | static_assert(sizeof(struct smr_barrier_job) == SMR_BARRIER_SIZE); |
1308 | #define SMR_BARRIER_USE_STACK (SMR_BARRIER_SIZE * MAX_CPUS <= 512) |
1309 | |
1310 | static void |
1311 | __smr_worker_check_invariants(struct smr_worker *smrw) |
1312 | { |
1313 | #if MACH_ASSERT |
1314 | smr_pcpu_t pcpu = smrw->whead; |
1315 | uint16_t num = (uint16_t)cpu_number(); |
1316 | |
1317 | assert(!ml_get_interrupts_enabled() || get_preemption_level()); |
1318 | |
1319 | for (; pcpu != *smrw->wold_tail; pcpu = pcpu->drain_next) { |
1320 | assertf(pcpu->qold_seq != SMR_SEQ_INVALID && |
1321 | __smr_pcpu_queued(pcpu), |
1322 | "pcpu %p doesn't belong on %p old queue" , pcpu, smrw); |
1323 | pcpu->__check_cpu = num; |
1324 | pcpu->__check_reason = (uint8_t)smrw->detach_reason; |
1325 | pcpu->__check_list = 1; |
1326 | } |
1327 | |
1328 | for (; pcpu != *smrw->wage_tail; pcpu = pcpu->drain_next) { |
1329 | __assert_only smr_t smr = pcpu->drain_smr; |
1330 | |
1331 | assertf(pcpu->qold_seq == SMR_SEQ_INVALID && |
1332 | pcpu->qage_seq != SMR_SEQ_INVALID && |
1333 | SMR_SEQ_CMP(pcpu->qage_seq, <=, smr->smr_clock.s_wr_seq) && |
1334 | __smr_pcpu_queued(pcpu), |
1335 | "pcpu %p doesn't belong on %p aging queue" , pcpu, smrw); |
1336 | pcpu->__check_cpu = num; |
1337 | pcpu->__check_reason = (uint8_t)smrw->detach_reason; |
1338 | pcpu->__check_list = 2; |
1339 | } |
1340 | |
1341 | for (; pcpu != *smrw->wcur_tail; pcpu = pcpu->drain_next) { |
1342 | assertf(pcpu->qold_seq == SMR_SEQ_INVALID && |
1343 | pcpu->qage_seq != SMR_SEQ_INVALID && |
1344 | __smr_pcpu_queued(pcpu), |
1345 | "pcpu %p doesn't belong on %p current queue" , pcpu, smrw); |
1346 | pcpu->__check_cpu = num; |
1347 | pcpu->__check_reason = (uint8_t)smrw->detach_reason; |
1348 | pcpu->__check_list = 3; |
1349 | } |
1350 | |
1351 | assert(pcpu == NULL); |
1352 | #else |
1353 | (void)smrw; |
1354 | #endif |
1355 | } |
1356 | |
1357 | __attribute__((noinline)) |
1358 | static void |
1359 | __smr_cpu_lazy_up(struct smr_worker *smrw) |
1360 | { |
1361 | spl_t spl; |
1362 | |
1363 | /* |
1364 | * calling smr_call/smr_barrier() from the context of a CPU |
1365 | * with a detached worker is illegal. |
1366 | * |
1367 | * However, bound threads might run on a derecommended (IGNORED) |
1368 | * cpu which we correct for here (and the CPU will go back to IGNORED |
1369 | * in smr_cpu_leave()). |
1370 | */ |
1371 | assert(smrw->detach_reason == SMR_CPU_REASON_IGNORED); |
1372 | |
1373 | spl = splsched(); |
1374 | __smrw_lock(smrw); |
1375 | smrw->detach_reason &= ~SMR_CPU_REASON_IGNORED; |
1376 | __smrw_unlock(smrw); |
1377 | splx(spl); |
1378 | } |
1379 | |
1380 | static void |
1381 | __smr_cpu_lazy_up_if_needed(struct smr_worker *smrw) |
1382 | { |
1383 | if (__improbable(smrw->detach_reason != SMR_CPU_REASON_NONE)) { |
1384 | __smr_cpu_lazy_up(smrw); |
1385 | } |
1386 | } |
1387 | |
1388 | static bool |
1389 | __smr_call_should_advance(smr_pcpu_t pcpu) |
1390 | { |
1391 | if (pcpu->qcur_cnt > smr_call_cnt_cap) { |
1392 | return true; |
1393 | } |
1394 | if (pcpu->qcur_size > smr_call_size_cap) { |
1395 | return true; |
1396 | } |
1397 | return false; |
1398 | } |
1399 | |
1400 | static void |
1401 | __smr_call_advance_qcur(smr_t smr, smr_pcpu_t pcpu, bool needs_commit) |
1402 | { |
1403 | smr_seq_t new_seq; |
1404 | |
1405 | if (needs_commit || pcpu->qage_seq) { |
1406 | new_seq = smr_advance(smr); |
1407 | } else { |
1408 | new_seq = smr_deferred_advance(smr); |
1409 | } |
1410 | __builtin_assume(new_seq != SMR_SEQ_INVALID); |
1411 | |
1412 | pcpu->qage_seq = new_seq; |
1413 | pcpu->qage_tail = pcpu->qcur_tail; |
1414 | |
1415 | pcpu->qcur_size = 0; |
1416 | pcpu->qcur_cnt = 0; |
1417 | } |
1418 | |
1419 | static void |
1420 | __smr_call_push(smr_pcpu_t pcpu, smr_node_t node, smr_cb_t cb) |
1421 | { |
1422 | assert(pcpu->c_rd_seq == SMR_SEQ_INVALID); |
1423 | |
1424 | node->smrn_next = NULL; |
1425 | node->smrn_cb = cb; |
1426 | |
1427 | *pcpu->qcur_tail = node; |
1428 | pcpu->qcur_tail = &node->smrn_next; |
1429 | pcpu->qcur_cnt += 1; |
1430 | } |
1431 | |
1432 | static void |
1433 | __smr_call_dispatch(struct smr_worker *smrw, smr_pcpu_t pcpu) |
1434 | { |
1435 | __smr_worker_check_invariants(smrw); |
1436 | |
1437 | if (!__smr_pcpu_queued(pcpu)) { |
1438 | assert(pcpu->qold_seq == SMR_SEQ_INVALID); |
1439 | assert(pcpu->qage_seq != SMR_SEQ_INVALID); |
1440 | |
1441 | pcpu->drain_next = NULL; |
1442 | *smrw->wcur_tail = pcpu; |
1443 | smrw->wcur_tail = &pcpu->drain_next; |
1444 | } |
1445 | } |
1446 | |
1447 | void |
1448 | smr_call(smr_t smr, smr_node_t node, vm_size_t size, smr_cb_t cb) |
1449 | { |
1450 | struct smr_worker *smrw; |
1451 | smr_pcpu_t pcpu; |
1452 | |
1453 | if (__improbable(startup_phase < STARTUP_SUB_EARLY_BOOT)) { |
1454 | return cb(node); |
1455 | } |
1456 | |
1457 | lock_disable_preemption_for_thread(current_thread()); |
1458 | assert(!ml_at_interrupt_context()); |
1459 | |
1460 | smrw = PERCPU_GET(smr_worker); |
1461 | __smr_cpu_lazy_up_if_needed(smrw); |
1462 | |
1463 | pcpu = __smr_pcpu(smr); |
1464 | assert(pcpu->c_rd_seq == SMR_SEQ_INVALID); |
1465 | |
1466 | if (os_add_overflow(pcpu->qcur_size, size, &pcpu->qcur_size)) { |
1467 | pcpu->qcur_size = UINT32_MAX; |
1468 | } |
1469 | |
1470 | __smr_call_push(pcpu, node, cb); |
1471 | if (__smr_call_should_advance(pcpu)) { |
1472 | if (pcpu->qage_seq == SMR_SEQ_INVALID) { |
1473 | __smr_call_advance_qcur(smr, pcpu, false); |
1474 | } |
1475 | __smr_call_dispatch(smrw, pcpu); |
1476 | } |
1477 | |
1478 | return lock_enable_preemption(); |
1479 | } |
1480 | |
1481 | static inline event_t |
1482 | __smrb_event(struct smr_barrier_ctx *ctx) |
1483 | { |
1484 | return ctx; |
1485 | } |
1486 | |
1487 | static void |
1488 | __smr_barrier_cb(struct smr_node *node) |
1489 | { |
1490 | struct smr_barrier_job *job; |
1491 | struct smr_barrier_ctx *ctx; |
1492 | |
1493 | job = __container_of(node, struct smr_barrier_job, smrj_node); |
1494 | ctx = job->smrj_context; |
1495 | |
1496 | if (os_atomic_dec(&ctx->smrb_pending, relaxed) == 0) { |
1497 | /* |
1498 | * It is permitted to still reach into the context |
1499 | * because smr_barrier() always blocks, which means |
1500 | * that the context will be valid until this wakeup |
1501 | * happens. |
1502 | */ |
1503 | thread_wakeup_thread(event: __smrb_event(ctx), thread: ctx->smrb_waiter); |
1504 | } |
1505 | } |
1506 | |
1507 | static bool |
1508 | __smr_barrier_drain(struct smr_worker *smrw, bool needs_commit) |
1509 | { |
1510 | mpsc_queue_chain_t head, tail, it; |
1511 | |
1512 | head = mpsc_queue_dequeue_batch(q: &smrw->barrier_queue, tail: &tail, |
1513 | OS_ATOMIC_DEPENDENCY_NONE); |
1514 | |
1515 | mpsc_queue_batch_foreach_safe(it, head, tail) { |
1516 | struct smr_barrier_job *job; |
1517 | struct smr_barrier_ctx *ctx; |
1518 | smr_pcpu_t pcpu; |
1519 | smr_t smr; |
1520 | |
1521 | job = __container_of(it, struct smr_barrier_job, smrj_link); |
1522 | ctx = job->smrj_context; |
1523 | smr = ctx->smrb_domain; |
1524 | pcpu = __smr_pcpu(smr, smrw->processor->cpu_id); |
1525 | |
1526 | pcpu->qcur_size = UINT32_MAX; |
1527 | __smr_call_push(pcpu, &job->smrj_node, __smr_barrier_cb); |
1528 | __smr_call_advance_qcur(smr, pcpu, needs_commit); |
1529 | __smr_call_dispatch(smrw, pcpu); |
1530 | } |
1531 | |
1532 | return head != NULL; |
1533 | } |
1534 | |
1535 | |
1536 | void |
1537 | smr_barrier(smr_t smr) |
1538 | { |
1539 | #if SMR_BARRIER_USE_STACK |
1540 | struct smr_barrier_job jobs[MAX_CPUS]; |
1541 | #else |
1542 | struct smr_barrier_job *jobs; |
1543 | #endif |
1544 | struct smr_barrier_job *job; |
1545 | struct smr_barrier_ctx ctx = { |
1546 | .smrb_domain = smr, |
1547 | .smrb_waiter = current_thread(), |
1548 | .smrb_pending = zpercpu_count(), |
1549 | .smrb_count = zpercpu_count(), |
1550 | }; |
1551 | spl_t spl; |
1552 | |
1553 | /* |
1554 | * First wait for all readers to observe whatever it is |
1555 | * that changed prior to this call. |
1556 | * |
1557 | * _then_ enqueue callbacks that push out anything ahead. |
1558 | */ |
1559 | smr_synchronize(smr); |
1560 | |
1561 | #if !SMR_BARRIER_USE_STACK |
1562 | jobs = kalloc_type(struct smr_barrier_job, ctx.smrb_count, |
1563 | Z_WAITOK | Z_ZERO | Z_NOFAIL); |
1564 | #endif |
1565 | job = jobs; |
1566 | spl = splsched(); |
1567 | |
1568 | __smr_cpu_lazy_up_if_needed(PERCPU_GET(smr_worker)); |
1569 | |
1570 | percpu_foreach(smrw, smr_worker) { |
1571 | job->smrj_context = &ctx; |
1572 | if (mpsc_queue_append(q: &smrw->barrier_queue, elm: &job->smrj_link)) { |
1573 | __smrw_lock(smrw); |
1574 | __smrw_wakeup_and_unlock(smrw); |
1575 | } |
1576 | job++; |
1577 | } |
1578 | |
1579 | /* |
1580 | * Because we disabled interrupts, our own CPU's callback |
1581 | * can't possibly have run, so just block. |
1582 | * |
1583 | * We must block in order to guarantee the lifetime of "ctx". |
1584 | * (See comment in __smr_barrier_cb). |
1585 | */ |
1586 | assert_wait(event: __smrb_event(ctx: &ctx), THREAD_UNINT); |
1587 | assert(ctx.smrb_pending > 0); |
1588 | splx(spl); |
1589 | thread_block(THREAD_CONTINUE_NULL); |
1590 | |
1591 | #if !SMR_BARRIER_USE_STACK |
1592 | kfree_type(struct smr_barrier_job, ctx.smrb_count, jobs); |
1593 | #endif |
1594 | } |
1595 | |
1596 | |
1597 | #pragma mark SMR domains: smr_worker |
1598 | |
1599 | static void |
1600 | __smr_worker_drain_lock(struct smr_worker *smrw) |
1601 | { |
1602 | for (;;) { |
1603 | ml_set_interrupts_enabled(false); |
1604 | __smrw_lock(smrw); |
1605 | |
1606 | /* |
1607 | * Check we are on an appropriate processor |
1608 | * |
1609 | * Note that we might be running on the canonical |
1610 | * processor incorrectly: if the processor has been |
1611 | * de-recommended but isn't offline. |
1612 | */ |
1613 | if (__probable(current_processor() == smrw->processor)) { |
1614 | if (__probable(!smrw->detach_reason)) { |
1615 | break; |
1616 | } |
1617 | } else { |
1618 | if (__probable(smrw->detach_reason)) { |
1619 | break; |
1620 | } |
1621 | } |
1622 | |
1623 | /* go bind in the right place and retry */ |
1624 | thread_bind(processor: __smrw_drain_bind_target(smrw)); |
1625 | __smrw_unlock(smrw); |
1626 | ml_set_interrupts_enabled(true); |
1627 | thread_block(THREAD_CONTINUE_NULL); |
1628 | } |
1629 | } |
1630 | |
1631 | static void |
1632 | __smr_worker_drain_unlock(struct smr_worker *smrw) |
1633 | { |
1634 | __smrw_unlock(smrw); |
1635 | ml_set_interrupts_enabled(true); |
1636 | } |
1637 | |
1638 | /*! |
1639 | * @function __smr_worker_tick |
1640 | * |
1641 | * @brief |
1642 | * Make the SMR worker queues make gentle progress |
1643 | * |
1644 | * @discussion |
1645 | * One round of progress will: |
1646 | * - move entries that have aged as being old, |
1647 | * - commit entries that have a deferred sequence and let them age. |
1648 | * |
1649 | * If this results into any callbacks to become "old", |
1650 | * then the worker is being woken up to start running callbacks. |
1651 | * |
1652 | * This function must run either on the processfor for this worker, |
1653 | * or under the worker drain lock being held. |
1654 | */ |
1655 | static void |
1656 | __smr_worker_tick(struct smr_worker *smrw, uint64_t ctime, bool wakeup) |
1657 | { |
1658 | smr_pcpu_t pcpu = *smrw->wold_tail; |
1659 | |
1660 | __smr_worker_check_invariants(smrw); |
1661 | |
1662 | for (; pcpu != *smrw->wage_tail; pcpu = pcpu->drain_next) { |
1663 | assert(pcpu->qold_seq == SMR_SEQ_INVALID); |
1664 | assert(pcpu->qage_seq != SMR_SEQ_INVALID); |
1665 | |
1666 | pcpu->qold_seq = pcpu->qage_seq; |
1667 | pcpu->qold_tail = pcpu->qage_tail; |
1668 | |
1669 | pcpu->qage_seq = SMR_SEQ_INVALID; |
1670 | } |
1671 | |
1672 | for (; pcpu; pcpu = pcpu->drain_next) { |
1673 | assert(pcpu->qold_seq == SMR_SEQ_INVALID); |
1674 | assert(pcpu->qage_seq != SMR_SEQ_INVALID); |
1675 | |
1676 | smr_deferred_advance_commit(smr: pcpu->drain_smr, seq: pcpu->qage_seq); |
1677 | } |
1678 | |
1679 | smrw->wold_tail = smrw->wage_tail; |
1680 | smrw->wage_tail = smrw->wcur_tail; |
1681 | smrw->drain_ctime = ctime; |
1682 | |
1683 | __smr_worker_check_invariants(smrw); |
1684 | |
1685 | if (wakeup && smrw->wold_tail != &smrw->whead) { |
1686 | __smrw_lock(smrw); |
1687 | __smrw_wakeup_and_unlock(smrw); |
1688 | } |
1689 | } |
1690 | |
1691 | static void |
1692 | __smr_worker_update_wold_tail(struct smr_worker *smrw, smr_pcpu_t *new_tail) |
1693 | { |
1694 | smr_pcpu_t *old_tail = smrw->wold_tail; |
1695 | |
1696 | if (smrw->wcur_tail == old_tail) { |
1697 | smrw->wage_tail = new_tail; |
1698 | smrw->wcur_tail = new_tail; |
1699 | } else if (smrw->wage_tail == old_tail) { |
1700 | smrw->wage_tail = new_tail; |
1701 | } |
1702 | |
1703 | smrw->wold_tail = new_tail; |
1704 | } |
1705 | |
1706 | static void |
1707 | __smr_worker_drain_one(struct smr_worker *smrw, smr_pcpu_t pcpu) |
1708 | { |
1709 | smr_t smr = pcpu->drain_smr; |
1710 | smr_seq_t seq = pcpu->qold_seq; |
1711 | smr_node_t head; |
1712 | |
1713 | /* |
1714 | * Step 1: pop the "old" items, |
1715 | * (qold_tail/qold_seq left dangling) |
1716 | */ |
1717 | |
1718 | assert(seq != SMR_SEQ_INVALID); |
1719 | head = pcpu->qhead; |
1720 | pcpu->qhead = *pcpu->qold_tail; |
1721 | *pcpu->qold_tail = NULL; |
1722 | |
1723 | /* |
1724 | * Step 2: Reconstruct the queue |
1725 | * based on the sequence numbers and count fields. |
1726 | * |
1727 | * Do what __smr_worker_tick() would do on this queue: |
1728 | * - commit the aging queue |
1729 | * - advance the current queue if needed |
1730 | */ |
1731 | |
1732 | if (pcpu->qage_seq != SMR_SEQ_INVALID) { |
1733 | assert(pcpu->qage_tail != pcpu->qold_tail); |
1734 | |
1735 | smr_deferred_advance_commit(smr, seq: pcpu->qage_seq); |
1736 | pcpu->qold_seq = pcpu->qage_seq; |
1737 | pcpu->qold_tail = pcpu->qage_tail; |
1738 | } else { |
1739 | assert(pcpu->qage_tail == pcpu->qold_tail); |
1740 | |
1741 | pcpu->qold_seq = SMR_SEQ_INVALID; |
1742 | pcpu->qold_tail = &pcpu->qhead; |
1743 | } |
1744 | |
1745 | if (__smr_call_should_advance(pcpu)) { |
1746 | __smr_call_advance_qcur(smr, pcpu, false); |
1747 | } else { |
1748 | pcpu->qage_seq = SMR_SEQ_INVALID; |
1749 | pcpu->qage_tail = pcpu->qold_tail; |
1750 | if (pcpu->qcur_cnt == 0) { |
1751 | pcpu->qcur_tail = pcpu->qage_tail; |
1752 | } |
1753 | } |
1754 | |
1755 | if (pcpu->qold_seq != SMR_SEQ_INVALID) { |
1756 | /* |
1757 | * The node has gained an "old seq" back, |
1758 | * it goes to the ready queue. |
1759 | */ |
1760 | pcpu->drain_next = *smrw->wold_tail; |
1761 | *smrw->wold_tail = pcpu; |
1762 | __smr_worker_update_wold_tail(smrw, |
1763 | new_tail: &pcpu->drain_next); |
1764 | } else if (pcpu->qage_seq != SMR_SEQ_INVALID) { |
1765 | /* |
1766 | * The node has gained an "age seq" back, |
1767 | * it needs to age and wait for a tick |
1768 | * for its sequence number to be commited. |
1769 | */ |
1770 | pcpu->drain_next = NULL; |
1771 | *smrw->wcur_tail = pcpu; |
1772 | smrw->wcur_tail = &pcpu->drain_next; |
1773 | } else { |
1774 | /* |
1775 | * The node is empty or with "current" |
1776 | * callbacks only, it can be dequeued. |
1777 | */ |
1778 | assert(!__smr_call_should_advance(pcpu)); |
1779 | pcpu->__check_cpu = (uint16_t)cpu_number(); |
1780 | pcpu->__check_reason = (uint8_t)smrw->detach_reason; |
1781 | pcpu->__check_list = 0; |
1782 | __smr_pcpu_set_not_queued(pcpu); |
1783 | } |
1784 | |
1785 | /* |
1786 | * Step 3: drain callbacks. |
1787 | */ |
1788 | __smr_worker_check_invariants(smrw); |
1789 | __smr_worker_drain_unlock(smrw); |
1790 | |
1791 | __smr_poll(smr, goal: seq, true); |
1792 | __smr_call_drain(head); |
1793 | |
1794 | __smr_worker_drain_lock(smrw); |
1795 | } |
1796 | |
1797 | static void |
1798 | __smr_worker_continue(void *arg, wait_result_t wr __unused) |
1799 | { |
1800 | smr_pcpu_t pcpu = NULL, next = NULL; |
1801 | struct smr_worker *const smrw = arg; |
1802 | uint64_t deadline; |
1803 | |
1804 | __smr_worker_drain_lock(smrw); |
1805 | __smr_worker_check_invariants(smrw); |
1806 | |
1807 | if (smrw->wold_tail != &smrw->whead) { |
1808 | next = smrw->whead; |
1809 | smrw->whead = *smrw->wold_tail; |
1810 | *smrw->wold_tail = NULL; |
1811 | __smr_worker_update_wold_tail(smrw, new_tail: &smrw->whead); |
1812 | } |
1813 | |
1814 | /* |
1815 | * The pipeline of per-cpu SMR data structures with pending |
1816 | * smr_call() callbacks has three stages: wcur -> wage -> wold. |
1817 | * |
1818 | * In order to guarantee forward progress, a tick happens |
1819 | * for each of them, either via __smr_worker_tick(), |
1820 | * or via __smr_worker_drain_one(). |
1821 | * |
1822 | * The second tick will happen either because to core stayed |
1823 | * busy enough that a subsequent smr_cpu_tick() decided to |
1824 | * perform it, or because the CPU idled, and smr_cpu_leave() |
1825 | * will perform an unconditional __smr_worker_tick(). |
1826 | */ |
1827 | __smr_barrier_drain(smrw, false); |
1828 | __smr_worker_tick(smrw, ctime: mach_absolute_time(), false); |
1829 | |
1830 | while ((pcpu = next)) { |
1831 | next = next->drain_next; |
1832 | __smr_worker_drain_one(smrw, pcpu); |
1833 | } |
1834 | |
1835 | if (__improbable(smrw->whead && smrw->detach_reason)) { |
1836 | /* |
1837 | * If the thread isn't bound, we want to flush anything |
1838 | * that is pending without causing too much contention. |
1839 | * |
1840 | * Sleep for a bit in order to give the system time |
1841 | * to observe any advance commits we did. |
1842 | */ |
1843 | deadline = mach_absolute_time() + cpu_checkin_min_interval; |
1844 | } else { |
1845 | deadline = TIMEOUT_WAIT_FOREVER; |
1846 | } |
1847 | waitq_assert_wait64_locked(waitq: &smrw->waitq, wait_event: __smrw_drain_event(smrw), |
1848 | THREAD_UNINT, TIMEOUT_URGENCY_SYS_NORMAL, deadline, |
1849 | TIMEOUT_NO_LEEWAY, thread: smrw->thread); |
1850 | |
1851 | /* |
1852 | * Make sure there's no barrier left, after we called assert_wait() |
1853 | * in order to pair with __smr_barrier_cb(). If we do find some, |
1854 | * we must be careful about invariants and forward progress. |
1855 | * |
1856 | * For affected domains, the dequeued barriers have been added |
1857 | * to their "qage" queue. If their "qage" queue was non empty, |
1858 | * then its "qage_seq" was already commited, and we must preserve |
1859 | * this invariant. |
1860 | * |
1861 | * Affected domains that were idle before will get enqueued on this |
1862 | * worker's "wcur" queue. In order to guarantee forward progress, |
1863 | * we must force a tick if both the "wage" and "wold" queues |
1864 | * of the worker are empty. |
1865 | */ |
1866 | if (__improbable(__smr_barrier_drain(smrw, true))) { |
1867 | if (smrw->wage_tail == &smrw->whead) { |
1868 | __smr_worker_tick(smrw, ctime: mach_absolute_time(), false); |
1869 | } |
1870 | } |
1871 | |
1872 | __smr_worker_check_invariants(smrw); |
1873 | __smr_worker_drain_unlock(smrw); |
1874 | |
1875 | thread_block_parameter(continuation: __smr_worker_continue, parameter: smrw); |
1876 | } |
1877 | |
1878 | |
1879 | #pragma mark SMR domains: scheduler integration |
1880 | |
1881 | #if CONFIG_QUIESCE_COUNTER |
1882 | __startup_data |
1883 | static uint64_t _Atomic quiesce_gen_startup; |
1884 | static uint64_t _Atomic *quiesce_genp = &quiesce_gen_startup; |
1885 | static uint64_t _Atomic quiesce_ctime; |
1886 | |
1887 | void |
1888 | cpu_quiescent_set_storage(uint64_t _Atomic *ptr) |
1889 | { |
1890 | /* |
1891 | * Transfer to the real location for the commpage. |
1892 | * |
1893 | * this is ok to do like this because the system |
1894 | * is still single threaded. |
1895 | */ |
1896 | uint64_t gen = os_atomic_load(&quiesce_gen_startup, relaxed); |
1897 | |
1898 | os_atomic_store(ptr, gen, relaxed); |
1899 | quiesce_genp = ptr; |
1900 | } |
1901 | |
1902 | static smr_seq_t |
1903 | cpu_quiescent_gen_to_seq(uint64_t gen) |
1904 | { |
1905 | return gen * SMR_SEQ_INC + SMR_SEQ_INIT; |
1906 | } |
1907 | |
1908 | static void |
1909 | cpu_quiescent_advance(uint64_t gen, uint64_t ctime __kdebug_only) |
1910 | { |
1911 | smr_seq_t seq = cpu_quiescent_gen_to_seq(gen); |
1912 | |
1913 | os_atomic_thread_fence(seq_cst); |
1914 | |
1915 | percpu_foreach(it, smr_worker) { |
1916 | smr_seq_t rd_seq = os_atomic_load(&it->rd_quiesce_seq, relaxed); |
1917 | |
1918 | if (rd_seq != SMR_SEQ_INVALID && SMR_SEQ_CMP(rd_seq, <, seq)) { |
1919 | return; |
1920 | } |
1921 | } |
1922 | |
1923 | os_atomic_thread_fence(seq_cst); |
1924 | |
1925 | if (lock_cmpxchg(quiesce_genp, gen, gen + 1, relaxed)) { |
1926 | KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_QUIESCENT_COUNTER), |
1927 | gen, 0, ctime, 0); |
1928 | } |
1929 | } |
1930 | |
1931 | static void |
1932 | cpu_quiescent_join(struct smr_worker *smrw) |
1933 | { |
1934 | uint64_t gen = os_atomic_load(quiesce_genp, relaxed); |
1935 | |
1936 | assert(smrw->rd_quiesce_seq == SMR_SEQ_INVALID); |
1937 | os_atomic_store(&smrw->rd_quiesce_seq, |
1938 | cpu_quiescent_gen_to_seq(gen), relaxed); |
1939 | os_atomic_thread_fence(seq_cst); |
1940 | } |
1941 | |
1942 | static void |
1943 | cpu_quiescent_tick(struct smr_worker *smrw, uint64_t ctime, uint64_t interval) |
1944 | { |
1945 | uint64_t gen = os_atomic_load(quiesce_genp, relaxed); |
1946 | smr_seq_t seq = cpu_quiescent_gen_to_seq(gen); |
1947 | |
1948 | if (smrw->rd_quiesce_seq == SMR_SEQ_INVALID) { |
1949 | /* |
1950 | * Likely called because of the scheduler tick, |
1951 | * smr_maintenance() will do the right thing. |
1952 | */ |
1953 | assert(current_processor()->state != PROCESSOR_RUNNING); |
1954 | } else if (seq != smrw->rd_quiesce_seq) { |
1955 | /* |
1956 | * Someone managed to update the sequence already, |
1957 | * learn it, update our ctime. |
1958 | */ |
1959 | os_atomic_store(&smrw->rd_quiesce_seq, seq, release); |
1960 | os_atomic_store(&quiesce_ctime, ctime, relaxed); |
1961 | os_atomic_thread_fence(seq_cst); |
1962 | } else if ((ctime - os_atomic_load(&quiesce_ctime, relaxed)) > interval) { |
1963 | /* |
1964 | * The system looks busy enough we want to update |
1965 | * the counter faster than every scheduler tick. |
1966 | */ |
1967 | os_atomic_store(&quiesce_ctime, ctime, relaxed); |
1968 | cpu_quiescent_advance(gen, ctime); |
1969 | } |
1970 | } |
1971 | |
1972 | static void |
1973 | cpu_quiescent_leave(struct smr_worker *smrw) |
1974 | { |
1975 | assert(smrw->rd_quiesce_seq != SMR_SEQ_INVALID); |
1976 | os_atomic_store(&smrw->rd_quiesce_seq, SMR_SEQ_INVALID, release); |
1977 | } |
1978 | #endif /* CONFIG_QUIESCE_COUNTER */ |
1979 | |
1980 | uint32_t |
1981 | smr_cpu_checkin_get_min_interval_us(void) |
1982 | { |
1983 | return cpu_checkin_min_interval_us; |
1984 | } |
1985 | |
1986 | void |
1987 | smr_cpu_checkin_set_min_interval_us(uint32_t new_value_us) |
1988 | { |
1989 | /* clamp to something vaguely sane */ |
1990 | if (new_value_us > CPU_CHECKIN_MIN_INTERVAL_MAX_US) { |
1991 | new_value_us = CPU_CHECKIN_MIN_INTERVAL_MAX_US; |
1992 | } |
1993 | |
1994 | cpu_checkin_min_interval_us = new_value_us; |
1995 | |
1996 | uint64_t abstime = 0; |
1997 | clock_interval_to_absolutetime_interval(interval: cpu_checkin_min_interval_us, |
1998 | NSEC_PER_USEC, result: &abstime); |
1999 | cpu_checkin_min_interval = abstime; |
2000 | } |
2001 | |
2002 | __startup_func |
2003 | static void |
2004 | smr_cpu_checkin_init_min_interval_us(void) |
2005 | { |
2006 | smr_cpu_checkin_set_min_interval_us(CPU_CHECKIN_MIN_INTERVAL_US); |
2007 | } |
2008 | STARTUP(TUNABLES, STARTUP_RANK_FIRST, smr_cpu_checkin_init_min_interval_us); |
2009 | |
2010 | static void |
2011 | __smr_cpu_init_thread(struct smr_worker *smrw) |
2012 | { |
2013 | char name[MAXTHREADNAMESIZE]; |
2014 | thread_t th = THREAD_NULL; |
2015 | |
2016 | kernel_thread_create(continuation: __smr_worker_continue, parameter: smrw, MINPRI_KERNEL, new_thread: &th); |
2017 | smrw->thread = th; |
2018 | |
2019 | snprintf(name, sizeof(name), "smr.reclaim:%d" , smrw->processor->cpu_id); |
2020 | thread_set_thread_name(th, name); |
2021 | thread_start_in_assert_wait(thread: th, |
2022 | waitq: &smrw->waitq, event: __smrw_drain_event(smrw), THREAD_UNINT); |
2023 | } |
2024 | |
2025 | void |
2026 | smr_cpu_init(struct processor *processor) |
2027 | { |
2028 | struct smr_worker *smrw; |
2029 | |
2030 | smrw = PERCPU_GET_RELATIVE(smr_worker, processor, processor); |
2031 | smrw->processor = processor; |
2032 | |
2033 | waitq_init(waitq: &smrw->waitq, type: WQT_QUEUE, SYNC_POLICY_FIFO); |
2034 | smrw->detach_reason = SMR_CPU_REASON_OFFLINE; |
2035 | |
2036 | smrq_init(&smrw->sect_queue); |
2037 | smrw->wold_tail = &smrw->whead; |
2038 | smrw->wage_tail = &smrw->whead; |
2039 | smrw->wcur_tail = &smrw->whead; |
2040 | mpsc_queue_init(q: &smrw->barrier_queue); |
2041 | |
2042 | if (processor != master_processor) { |
2043 | __smr_cpu_init_thread(smrw); |
2044 | } |
2045 | } |
2046 | STARTUP_ARG(LOCKS, STARTUP_RANK_LAST, smr_cpu_init, master_processor); |
2047 | STARTUP_ARG(THREAD_CALL, STARTUP_RANK_LAST, |
2048 | __smr_cpu_init_thread, PERCPU_GET_MASTER(smr_worker)); |
2049 | |
2050 | /*! |
2051 | * @function smr_cpu_up() |
2052 | * |
2053 | * @brief |
2054 | * Scheduler callback to notify this processor is going up. |
2055 | * |
2056 | * @discussion |
2057 | * Called at splsched() under the sched_available_cores_lock. |
2058 | */ |
2059 | void |
2060 | smr_cpu_up(struct processor *processor, smr_cpu_reason_t reason) |
2061 | { |
2062 | struct smr_worker *smrw; |
2063 | |
2064 | smrw = PERCPU_GET_RELATIVE(smr_worker, processor, processor); |
2065 | |
2066 | __smrw_lock(smrw); |
2067 | if (reason != SMR_CPU_REASON_IGNORED) { |
2068 | assert((smrw->detach_reason & reason) == reason); |
2069 | } |
2070 | smrw->detach_reason &= ~reason; |
2071 | __smrw_unlock(smrw); |
2072 | } |
2073 | |
2074 | static void |
2075 | __smr_cpu_down_and_unlock( |
2076 | struct processor *processor, |
2077 | struct smr_worker *smrw, |
2078 | smr_cpu_reason_t reason) |
2079 | { |
2080 | bool detach = !smrw->detach_reason; |
2081 | |
2082 | /* |
2083 | * When reason is SMR_CPU_REASON_IGNORED, |
2084 | * this is called from smr_cpu_leave() on the way to idle. |
2085 | * |
2086 | * However this isn't sychronized with the recommendation |
2087 | * lock, hence it is possible that the CPU might actually |
2088 | * be recommended again while we're on the way to idle. |
2089 | * |
2090 | * By re-checking processor recommendation under |
2091 | * the __smrw_lock, we serialize with smr_cpu_up(). |
2092 | */ |
2093 | if (reason != SMR_CPU_REASON_IGNORED) { |
2094 | assert((smrw->detach_reason & reason) == 0); |
2095 | } else if (processor->is_recommended) { |
2096 | /* |
2097 | * The race we try to detect happened, |
2098 | * do nothing. |
2099 | */ |
2100 | reason = SMR_CPU_REASON_NONE; |
2101 | detach = false; |
2102 | } |
2103 | smrw->detach_reason |= reason; |
2104 | reason = smrw->detach_reason; |
2105 | |
2106 | if (detach && smrw->whead) { |
2107 | detach = !__smrw_wakeup_and_unlock(smrw); |
2108 | } else { |
2109 | __smrw_unlock(smrw); |
2110 | } |
2111 | |
2112 | if (detach) { |
2113 | thread_unbind_after_queue_shutdown(thread: smrw->thread, processor); |
2114 | } |
2115 | } |
2116 | |
2117 | /*! |
2118 | * @function smr_cpu_down() |
2119 | * |
2120 | * @brief |
2121 | * Scheduler callback to notify this processor is going down. |
2122 | * |
2123 | * @discussion |
2124 | * Called at splsched() when the processor run queue is being shut down. |
2125 | */ |
2126 | void |
2127 | smr_cpu_down(struct processor *processor, smr_cpu_reason_t reason) |
2128 | { |
2129 | struct smr_worker *smrw; |
2130 | |
2131 | smrw = PERCPU_GET_RELATIVE(smr_worker, processor, processor); |
2132 | |
2133 | __smrw_lock(smrw); |
2134 | __smr_cpu_down_and_unlock(processor, smrw, reason); |
2135 | } |
2136 | |
2137 | |
2138 | /*! |
2139 | * @function smr_cpu_join() |
2140 | * |
2141 | * @brief |
2142 | * Scheduler callback to notify this processor is going out of idle. |
2143 | * |
2144 | * @discussion |
2145 | * Called at splsched(). |
2146 | */ |
2147 | void |
2148 | smr_cpu_join(struct processor *processor, uint64_t ctime __unused) |
2149 | { |
2150 | #if CONFIG_QUIESCE_COUNTER |
2151 | struct smr_worker *smrw; |
2152 | |
2153 | smrw = PERCPU_GET_RELATIVE(smr_worker, processor, processor); |
2154 | cpu_quiescent_join(smrw); |
2155 | #else |
2156 | (void)processor; |
2157 | #endif /* CONFIG_QUIESCE_COUNTER */ |
2158 | } |
2159 | |
2160 | /*! |
2161 | * @function smr_cpu_tick() |
2162 | * |
2163 | * @brief |
2164 | * Scheduler callback invoked during the scheduler maintenance routine. |
2165 | * |
2166 | * @discussion |
2167 | * Called at splsched(). |
2168 | */ |
2169 | void |
2170 | smr_cpu_tick(uint64_t ctime, bool safe_point) |
2171 | { |
2172 | struct smr_worker *smrw = PERCPU_GET(smr_worker); |
2173 | uint64_t interval = cpu_checkin_min_interval; |
2174 | |
2175 | #if CONFIG_QUIESCE_COUNTER |
2176 | cpu_quiescent_tick(smrw, ctime, interval); |
2177 | #endif /* CONFIG_QUIESCE_COUNTER */ |
2178 | |
2179 | /* |
2180 | * if a bound thread was woken up on a derecommended core, |
2181 | * our detach_reason might be "IGNORED" and we want to leave |
2182 | * it alone in that case |
2183 | */ |
2184 | if (safe_point && !smrw->detach_reason && smrw->whead && |
2185 | current_processor()->state == PROCESSOR_RUNNING && |
2186 | (ctime - smrw->drain_ctime) > interval) { |
2187 | __smr_worker_tick(smrw, ctime, true); |
2188 | } |
2189 | } |
2190 | |
2191 | /*! |
2192 | * @function smr_cpu_leave() |
2193 | * |
2194 | * @brief |
2195 | * Scheduler callback to notify this processor is going idle. |
2196 | * |
2197 | * @discussion |
2198 | * Called at splsched(). |
2199 | */ |
2200 | void |
2201 | smr_cpu_leave(struct processor *processor, uint64_t ctime) |
2202 | { |
2203 | struct smr_worker *smrw; |
2204 | |
2205 | smrw = PERCPU_GET_RELATIVE(smr_worker, processor, processor); |
2206 | |
2207 | /* |
2208 | * if a bound thread was woken up on a derecommended core, |
2209 | * our detach_reason might be "IGNORED" and we want to leave |
2210 | * it alone in that case |
2211 | * |
2212 | * See comment in __smr_worker_continue for why this must be |
2213 | * done unconditionally otherwise. |
2214 | */ |
2215 | if (!smrw->detach_reason && smrw->whead) { |
2216 | __smr_worker_tick(smrw, ctime, true); |
2217 | } |
2218 | |
2219 | if (__improbable(!processor->is_recommended)) { |
2220 | __smrw_lock(smrw); |
2221 | __smr_cpu_down_and_unlock(processor, smrw, reason: SMR_CPU_REASON_IGNORED); |
2222 | } |
2223 | |
2224 | #if CONFIG_QUIESCE_COUNTER |
2225 | cpu_quiescent_leave(smrw); |
2226 | #endif /* CONFIG_QUIESCE_COUNTER */ |
2227 | } |
2228 | |
2229 | /*! |
2230 | * @function smr_maintenance() |
2231 | * |
2232 | * @brief |
2233 | * Scheduler callback called at the scheduler tick. |
2234 | * |
2235 | * @discussion |
2236 | * Called at splsched(). |
2237 | */ |
2238 | void |
2239 | smr_maintenance(uint64_t ctime) |
2240 | { |
2241 | #if CONFIG_QUIESCE_COUNTER |
2242 | cpu_quiescent_advance(os_atomic_load(quiesce_genp, relaxed), ctime); |
2243 | #else |
2244 | (void)ctime; |
2245 | #endif /* CONFIG_QUIESCE_COUNTER */ |
2246 | } |
2247 | |
2248 | |
2249 | #pragma mark - SMR hash tables |
2250 | |
2251 | static struct smrq_slist_head * |
2252 | smr_hash_alloc_array(size_t size) |
2253 | { |
2254 | return kalloc_type(struct smrq_slist_head, size, |
2255 | Z_WAITOK | Z_ZERO | Z_SPRAYQTN); |
2256 | } |
2257 | |
2258 | static void |
2259 | smr_hash_free_array(struct smrq_slist_head *array, size_t size) |
2260 | { |
2261 | kfree_type(struct smrq_slist_head, size, array); |
2262 | } |
2263 | |
2264 | static inline uintptr_t |
2265 | smr_hash_array_encode(struct smrq_slist_head *array, uint16_t order) |
2266 | { |
2267 | uintptr_t ptr; |
2268 | |
2269 | ptr = (uintptr_t)array; |
2270 | ptr &= ~SMRH_ARRAY_ORDER_MASK; |
2271 | ptr |= (uintptr_t)order << SMRH_ARRAY_ORDER_SHIFT; |
2272 | |
2273 | return ptr; |
2274 | } |
2275 | |
2276 | #pragma mark SMR simple hash tables |
2277 | |
2278 | void |
2279 | smr_hash_init(struct smr_hash *smrh, size_t size) |
2280 | { |
2281 | struct smrq_slist_head *array; |
2282 | uint16_t shift; |
2283 | |
2284 | assert(size); |
2285 | shift = (uint16_t)flsll(mask: size - 1); |
2286 | size = 1UL << shift; |
2287 | if (startup_phase >= STARTUP_SUB_LOCKDOWN) { |
2288 | assert(size * sizeof(struct smrq_slist_head) <= |
2289 | KALLOC_SAFE_ALLOC_SIZE); |
2290 | } |
2291 | array = smr_hash_alloc_array(size); |
2292 | |
2293 | *smrh = (struct smr_hash){ |
2294 | .smrh_array = smr_hash_array_encode(array, order: 64 - shift), |
2295 | }; |
2296 | } |
2297 | |
2298 | void |
2299 | smr_hash_destroy(struct smr_hash *smrh) |
2300 | { |
2301 | struct smr_hash_array array = smr_hash_array_decode(smrh); |
2302 | |
2303 | smr_hash_free_array(array: array.smrh_array, size: smr_hash_size(array)); |
2304 | *smrh = (struct smr_hash){ }; |
2305 | } |
2306 | |
2307 | void |
2308 | __smr_hash_serialized_clear( |
2309 | struct smr_hash *smrh, |
2310 | smrh_traits_t smrht, |
2311 | void (^free)(void *obj)) |
2312 | { |
2313 | struct smr_hash_array array = smr_hash_array_decode(smrh); |
2314 | |
2315 | for (size_t i = 0; i < smr_hash_size(array); i++) { |
2316 | struct smrq_slink *link; |
2317 | __smrq_slink_t *prev; |
2318 | |
2319 | prev = &array.smrh_array[i].first; |
2320 | while ((link = smr_serialized_load(prev))) { |
2321 | prev = &link->next; |
2322 | free(__smrht_link_to_obj(traits: smrht, link)); |
2323 | } |
2324 | |
2325 | smr_clear_store(&array.smrh_array[i].first); |
2326 | } |
2327 | |
2328 | smrh->smrh_count = 0; |
2329 | } |
2330 | |
2331 | kern_return_t |
2332 | __smr_hash_shrink_and_unlock( |
2333 | struct smr_hash *smrh, |
2334 | lck_mtx_t *lock, |
2335 | smrh_traits_t smrht) |
2336 | { |
2337 | struct smr_hash_array decptr = smr_hash_array_decode(smrh); |
2338 | struct smrq_slist_head *newarray, *oldarray; |
2339 | uint16_t neworder = decptr.smrh_order + 1; |
2340 | size_t oldsize = smr_hash_size(array: decptr); |
2341 | size_t newsize = oldsize / 2; |
2342 | |
2343 | assert(newsize); |
2344 | |
2345 | if (os_atomic_load(&smrh->smrh_resizing, relaxed)) { |
2346 | lck_mtx_unlock(lck: lock); |
2347 | return KERN_FAILURE; |
2348 | } |
2349 | |
2350 | os_atomic_store(&smrh->smrh_resizing, true, relaxed); |
2351 | lck_mtx_unlock(lck: lock); |
2352 | |
2353 | newarray = smr_hash_alloc_array(size: newsize); |
2354 | if (newarray == NULL) { |
2355 | os_atomic_store(&smrh->smrh_resizing, false, relaxed); |
2356 | return KERN_RESOURCE_SHORTAGE; |
2357 | } |
2358 | |
2359 | lck_mtx_lock(lck: lock); |
2360 | |
2361 | /* |
2362 | * Step 1: collapse all the chains in pairs. |
2363 | */ |
2364 | oldarray = decptr.smrh_array; |
2365 | |
2366 | for (size_t i = 0; i < newsize; i++) { |
2367 | newarray[i] = oldarray[i]; |
2368 | smrq_serialized_append(&newarray[i], &oldarray[i + newsize]); |
2369 | } |
2370 | |
2371 | /* |
2372 | * Step 2: publish the new array. |
2373 | */ |
2374 | os_atomic_store(&smrh->smrh_array, |
2375 | smr_hash_array_encode(newarray, neworder), release); |
2376 | |
2377 | os_atomic_store(&smrh->smrh_resizing, false, relaxed); |
2378 | |
2379 | lck_mtx_unlock(lck: lock); |
2380 | |
2381 | /* |
2382 | * Step 3: free the old array once readers can't observe the old values. |
2383 | */ |
2384 | smr_synchronize(smr: smrht->domain); |
2385 | |
2386 | smr_hash_free_array(array: oldarray, size: oldsize); |
2387 | return KERN_SUCCESS; |
2388 | } |
2389 | |
2390 | kern_return_t |
2391 | __smr_hash_grow_and_unlock( |
2392 | struct smr_hash *smrh, |
2393 | lck_mtx_t *lock, |
2394 | smrh_traits_t smrht) |
2395 | { |
2396 | struct smr_hash_array decptr = smr_hash_array_decode(smrh); |
2397 | struct smrq_slist_head *newarray, *oldarray; |
2398 | __smrq_slink_t **prevarray; |
2399 | uint16_t neworder = decptr.smrh_order - 1; |
2400 | size_t oldsize = smr_hash_size(array: decptr); |
2401 | size_t newsize = 2 * oldsize; |
2402 | bool needs_another_round = false; |
2403 | |
2404 | if (smrh->smrh_resizing) { |
2405 | lck_mtx_unlock(lck: lock); |
2406 | return KERN_FAILURE; |
2407 | } |
2408 | |
2409 | smrh->smrh_resizing = true; |
2410 | lck_mtx_unlock(lck: lock); |
2411 | |
2412 | newarray = smr_hash_alloc_array(size: newsize); |
2413 | if (newarray == NULL) { |
2414 | os_atomic_store(&smrh->smrh_resizing, false, relaxed); |
2415 | return KERN_RESOURCE_SHORTAGE; |
2416 | } |
2417 | |
2418 | prevarray = kalloc_type(__smrq_slink_t *, newsize, |
2419 | Z_WAITOK | Z_ZERO | Z_SPRAYQTN); |
2420 | if (prevarray == NULL) { |
2421 | smr_hash_free_array(array: newarray, size: newsize); |
2422 | os_atomic_store(&smrh->smrh_resizing, false, relaxed); |
2423 | return KERN_RESOURCE_SHORTAGE; |
2424 | } |
2425 | |
2426 | |
2427 | lck_mtx_lock(lck: lock); |
2428 | |
2429 | /* |
2430 | * Step 1: create a duplicated array with twice as many heads. |
2431 | */ |
2432 | oldarray = decptr.smrh_array; |
2433 | |
2434 | memcpy(dst: newarray, src: oldarray, n: oldsize * sizeof(newarray[0])); |
2435 | memcpy(dst: newarray + oldsize, src: oldarray, n: oldsize * sizeof(newarray[0])); |
2436 | |
2437 | /* |
2438 | * Step 2: Publish the new array, and wait for readers to observe it |
2439 | * before we do any change. |
2440 | */ |
2441 | os_atomic_store(&smrh->smrh_array, |
2442 | smr_hash_array_encode(newarray, neworder), release); |
2443 | |
2444 | smr_synchronize(smr: smrht->domain); |
2445 | |
2446 | |
2447 | /* |
2448 | * Step 3: split the lists. |
2449 | */ |
2450 | |
2451 | /* |
2452 | * If the list we are trying to split looked like this, |
2453 | * where L elements will go to the "left" bucket and "R" |
2454 | * to the right one: |
2455 | * |
2456 | * old_head --> L1 --> L2 -> L5 |
2457 | * \ / \ |
2458 | * -> R3 --> R4 -> R6 --> NULL |
2459 | * |
2460 | * Then make sure the new heads point to their legitimate first element, |
2461 | * leading to this state: |
2462 | * |
2463 | * l_head --> L1 --> L2 -> L5 |
2464 | * \ / \ |
2465 | * r_head ----------------> R3 --> R4 -> R6 --> NULL |
2466 | * |
2467 | * |
2468 | * prevarray[left] = &L2->next |
2469 | * prevarray[right] = &r_head |
2470 | * oldarray[old] = L2 |
2471 | */ |
2472 | |
2473 | for (size_t i = 0; i < oldsize; i++) { |
2474 | struct smrq_slink *link, *next; |
2475 | uint32_t want_mask; |
2476 | |
2477 | link = smr_serialized_load(&oldarray[i].first); |
2478 | if (link == NULL) { |
2479 | continue; |
2480 | } |
2481 | |
2482 | want_mask = smrht->obj_hash(link, 0) & oldsize; |
2483 | while ((next = smr_serialized_load(&link->next)) && |
2484 | (smrht->obj_hash(next, 0) & oldsize) == want_mask) { |
2485 | link = next; |
2486 | } |
2487 | |
2488 | if (want_mask == 0) { |
2489 | /* elements seen go to the "left" bucket */ |
2490 | prevarray[i] = &link->next; |
2491 | prevarray[i + oldsize] = &newarray[i + oldsize].first; |
2492 | smr_serialized_store_relaxed(prevarray[i + oldsize], next); |
2493 | } else { |
2494 | /* elements seen go to the "right" bucket */ |
2495 | prevarray[i] = &newarray[i].first; |
2496 | prevarray[i + oldsize] = &link->next; |
2497 | smr_serialized_store_relaxed(prevarray[i], next); |
2498 | } |
2499 | |
2500 | smr_serialized_store_relaxed(&oldarray[i].first, |
2501 | next ? link : NULL); |
2502 | |
2503 | needs_another_round |= (next != NULL); |
2504 | } |
2505 | |
2506 | /* |
2507 | * At this point, when we split further, we must wait for |
2508 | * readers to observe the previous state before we split |
2509 | * further. Indeed, reusing the example above, the next |
2510 | * round of splitting would end up with this: |
2511 | * |
2512 | * l_head --> L1 --> L2 ----------------> L5 |
2513 | * / \ |
2514 | * r_head ----------------> R3 --> R4 -> R6 --> NULL |
2515 | * |
2516 | * |
2517 | * prevarray[left] = &L2->next |
2518 | * prevarray[right] = &R4->next |
2519 | * oldarray[old] = R4 |
2520 | * |
2521 | * But we must be sure that no readers can observe r_head |
2522 | * having been L1, otherwise a stale reader might skip over |
2523 | * R3/R4. |
2524 | * |
2525 | * Generally speaking we need to do that each time we do a round |
2526 | * of splitting that isn't terminating the list with NULL. |
2527 | */ |
2528 | |
2529 | while (needs_another_round) { |
2530 | smr_synchronize(smr: smrht->domain); |
2531 | |
2532 | needs_another_round = false; |
2533 | |
2534 | for (size_t i = 0; i < oldsize; i++) { |
2535 | struct smrq_slink *link, *next; |
2536 | uint32_t want_mask; |
2537 | |
2538 | link = smr_serialized_load(&oldarray[i].first); |
2539 | if (link == NULL) { |
2540 | continue; |
2541 | } |
2542 | |
2543 | /* |
2544 | * If `prevarray[i]` (left) points to the linkage |
2545 | * we stopped at, then it means the next element |
2546 | * will be "to the right" and vice versa. |
2547 | * |
2548 | * We also already know "next" exists, so only probe |
2549 | * after it. |
2550 | */ |
2551 | if (prevarray[i] == &link->next) { |
2552 | want_mask = (uint32_t)oldsize; |
2553 | } else { |
2554 | want_mask = 0; |
2555 | } |
2556 | |
2557 | link = smr_serialized_load(&link->next); |
2558 | |
2559 | while ((next = smr_serialized_load(&link->next)) && |
2560 | (smrht->obj_hash(next, 0) & oldsize) == want_mask) { |
2561 | link = next; |
2562 | } |
2563 | |
2564 | if (want_mask == 0) { |
2565 | /* elements seen go to the "left" bucket */ |
2566 | prevarray[i] = &link->next; |
2567 | smr_serialized_store_relaxed(prevarray[i + oldsize], next); |
2568 | } else { |
2569 | /* elements seen go to the "right" bucket */ |
2570 | smr_serialized_store_relaxed(prevarray[i], next); |
2571 | prevarray[i + oldsize] = &link->next; |
2572 | } |
2573 | |
2574 | smr_serialized_store_relaxed(&oldarray[i].first, |
2575 | next ? link : NULL); |
2576 | |
2577 | needs_another_round |= (next != NULL); |
2578 | } |
2579 | } |
2580 | |
2581 | smrh->smrh_resizing = false; |
2582 | lck_mtx_unlock(lck: lock); |
2583 | |
2584 | /* |
2585 | * Step 4: cleanup, no need to wait for readers, this happened already |
2586 | * at least once for splitting reasons. |
2587 | */ |
2588 | smr_hash_free_array(array: oldarray, size: oldsize); |
2589 | kfree_type(__smrq_slink_t *, newsize, prevarray); |
2590 | return KERN_SUCCESS; |
2591 | } |
2592 | |
2593 | #pragma mark SMR scalable hash tables |
2594 | |
2595 | #define SMRSH_MIGRATED ((struct smrq_slink *)SMRSH_BUCKET_STOP_BIT) |
2596 | static LCK_GRP_DECLARE(smr_shash_grp, "smr_shash" ); |
2597 | |
2598 | static inline size_t |
2599 | __smr_shash_min_size(struct smr_shash *smrh) |
2600 | { |
2601 | return 1ul << smrh->smrsh_min_shift; |
2602 | } |
2603 | |
2604 | static inline size_t |
2605 | __smr_shash_size_for_shift(uint8_t shift) |
2606 | { |
2607 | return (~0u >> shift) + 1; |
2608 | } |
2609 | |
2610 | static inline size_t |
2611 | __smr_shash_cursize(smrsh_state_t state) |
2612 | { |
2613 | return __smr_shash_size_for_shift(shift: state.curshift); |
2614 | } |
2615 | |
2616 | static void |
2617 | __smr_shash_bucket_init(hw_lck_ptr_t *head) |
2618 | { |
2619 | hw_lck_ptr_init(head, __smr_shash_bucket_stop(head), &smr_shash_grp); |
2620 | } |
2621 | |
2622 | static void |
2623 | __smr_shash_bucket_destroy(hw_lck_ptr_t *head) |
2624 | { |
2625 | hw_lck_ptr_destroy(head, &smr_shash_grp); |
2626 | } |
2627 | |
2628 | __attribute__((noinline)) |
2629 | void * |
2630 | __smr_shash_entered_find_slow( |
2631 | const struct smr_shash *smrh, |
2632 | smrh_key_t key, |
2633 | hw_lck_ptr_t *head, |
2634 | smrh_traits_t traits) |
2635 | { |
2636 | struct smrq_slink *link; |
2637 | smrsh_state_t state; |
2638 | uint32_t hash; |
2639 | |
2640 | /* wait for the rehashing to be done into their target buckets */ |
2641 | hw_lck_ptr_wait_for_value(head, SMRSH_MIGRATED, &smr_shash_grp); |
2642 | |
2643 | state = os_atomic_load(&smrh->smrsh_state, dependency); |
2644 | hash = __smr_shash_hash(smrh, idx: state.newidx, key, traits); |
2645 | head = __smr_shash_bucket(smrh, state, sel: SMRSH_NEW, hash); |
2646 | |
2647 | link = hw_lck_ptr_value(lck: head); |
2648 | while (!__smr_shash_is_stop(link)) { |
2649 | if (traits->obj_equ(link, key)) { |
2650 | return __smrht_link_to_obj(traits, link); |
2651 | } |
2652 | link = smr_entered_load(&link->next); |
2653 | } |
2654 | |
2655 | assert(link == __smr_shash_bucket_stop(head)); |
2656 | return NULL; |
2657 | } |
2658 | |
2659 | static const uint8_t __smr_shash_grow_ratio[] = { |
2660 | [SMRSH_COMPACT] = 6, |
2661 | [SMRSH_BALANCED] = 4, |
2662 | [SMRSH_BALANCED_NOSHRINK] = 4, |
2663 | [SMRSH_FASTEST] = 2, |
2664 | }; |
2665 | |
2666 | static inline uint64_t |
2667 | __smr_shash_count(struct smr_shash *smrh) |
2668 | { |
2669 | int64_t count = (int64_t)counter_load(&smrh->smrsh_count); |
2670 | |
2671 | /* |
2672 | * negative values make no sense and is likely due to some |
2673 | * stale values being read. |
2674 | */ |
2675 | return count < 0 ? 0ull : (uint64_t)count; |
2676 | } |
2677 | |
2678 | static inline bool |
2679 | __smr_shash_should_grow( |
2680 | struct smr_shash *smrh, |
2681 | smrsh_state_t state, |
2682 | uint64_t count) |
2683 | { |
2684 | size_t size = __smr_shash_cursize(state); |
2685 | |
2686 | /* grow if elem:bucket ratio is worse than grow_ratio:1 */ |
2687 | return count > __smr_shash_grow_ratio[smrh->smrsh_policy] * size; |
2688 | } |
2689 | |
2690 | static inline bool |
2691 | __smr_shash_should_reseed( |
2692 | struct smr_shash *smrh, |
2693 | size_t observed_depth) |
2694 | { |
2695 | return observed_depth > 10 * __smr_shash_grow_ratio[smrh->smrsh_policy]; |
2696 | } |
2697 | |
2698 | static inline bool |
2699 | __smr_shash_should_shrink( |
2700 | struct smr_shash *smrh, |
2701 | smrsh_state_t state, |
2702 | uint64_t count) |
2703 | { |
2704 | size_t size = __smr_shash_cursize(state); |
2705 | |
2706 | switch (smrh->smrsh_policy) { |
2707 | case SMRSH_COMPACT: |
2708 | /* shrink if bucket:elem ratio is worse than 1:1 */ |
2709 | return size > count && size > __smr_shash_min_size(smrh); |
2710 | case SMRSH_BALANCED: |
2711 | /* shrink if bucket:elem ratio is worse than 2:1 */ |
2712 | return size > 2 * count && size > __smr_shash_min_size(smrh); |
2713 | case SMRSH_BALANCED_NOSHRINK: |
2714 | case SMRSH_FASTEST: |
2715 | return false; |
2716 | } |
2717 | } |
2718 | |
2719 | static inline void |
2720 | __smr_shash_schedule_rehash( |
2721 | struct smr_shash *smrh, |
2722 | smrh_traits_t traits, |
2723 | smrsh_rehash_t reason) |
2724 | { |
2725 | smrsh_rehash_t rehash; |
2726 | |
2727 | rehash = os_atomic_load(&smrh->smrsh_rehashing, relaxed); |
2728 | if (rehash & reason) { |
2729 | return; |
2730 | } |
2731 | |
2732 | rehash = os_atomic_or_orig(&smrh->smrsh_rehashing, reason, relaxed); |
2733 | if (!rehash) { |
2734 | thread_call_enter1(call: smrh->smrsh_callout, |
2735 | __DECONST(void *, traits)); |
2736 | } |
2737 | } |
2738 | |
2739 | void * |
2740 | __smr_shash_entered_get_or_insert( |
2741 | struct smr_shash *smrh, |
2742 | smrh_key_t key, |
2743 | struct smrq_slink *link, |
2744 | smrh_traits_t traits) |
2745 | { |
2746 | struct smrq_slink *first; |
2747 | struct smrq_slink *other; |
2748 | uint32_t hash, depth; |
2749 | smrsh_state_t state; |
2750 | hw_lck_ptr_t *head; |
2751 | void *obj; |
2752 | |
2753 | state = os_atomic_load(&smrh->smrsh_state, dependency); |
2754 | hash = __smr_shash_hash(smrh, idx: state.curidx, key, traits); |
2755 | head = __smr_shash_bucket(smrh, state, sel: SMRSH_CUR, hash); |
2756 | first = hw_lck_ptr_lock(head, &smr_shash_grp); |
2757 | |
2758 | if (__improbable(first == SMRSH_MIGRATED)) { |
2759 | hw_lck_ptr_unlock_nopreempt(head, first, &smr_shash_grp); |
2760 | |
2761 | state = os_atomic_load(&smrh->smrsh_state, dependency); |
2762 | hash = __smr_shash_hash(smrh, idx: state.newidx, key, traits); |
2763 | head = __smr_shash_bucket(smrh, state, sel: SMRSH_NEW, hash); |
2764 | first = hw_lck_ptr_lock_nopreempt(head, &smr_shash_grp); |
2765 | } |
2766 | |
2767 | depth = 0; |
2768 | other = first; |
2769 | while (!__smr_shash_is_stop(link: other)) { |
2770 | depth++; |
2771 | if (traits->obj_equ(other, key)) { |
2772 | obj = __smrht_link_to_obj(traits, link: other); |
2773 | if (traits->obj_try_get(obj)) { |
2774 | hw_lck_ptr_unlock(head, first, |
2775 | &smr_shash_grp); |
2776 | return obj; |
2777 | } |
2778 | break; |
2779 | } |
2780 | other = smr_serialized_load(&other->next); |
2781 | } |
2782 | |
2783 | counter_inc_preemption_disabled(&smrh->smrsh_count); |
2784 | smr_serialized_store_relaxed(&link->next, first); |
2785 | hw_lck_ptr_unlock(head, link, &smr_shash_grp); |
2786 | |
2787 | if (__smr_shash_should_reseed(smrh, observed_depth: depth)) { |
2788 | __smr_shash_schedule_rehash(smrh, traits, reason: SMRSH_REHASH_RESEED); |
2789 | } else if (depth * 2 >= __smr_shash_grow_ratio[smrh->smrsh_policy] && |
2790 | __smr_shash_should_grow(smrh, state, count: __smr_shash_count(smrh))) { |
2791 | __smr_shash_schedule_rehash(smrh, traits, reason: SMRSH_REHASH_GROW); |
2792 | } |
2793 | return NULL; |
2794 | } |
2795 | |
2796 | __abortlike |
2797 | static void |
2798 | __smr_shash_missing_elt_panic( |
2799 | struct smr_shash *smrh, |
2800 | struct smrq_slink *link, |
2801 | smrh_traits_t traits) |
2802 | { |
2803 | panic("Unable to find item %p (linkage %p) in %p (traits %p)" , |
2804 | __smrht_link_to_obj(traits, link), link, smrh, traits); |
2805 | } |
2806 | |
2807 | smr_shash_mut_cursor_t |
2808 | __smr_shash_entered_mut_begin( |
2809 | struct smr_shash *smrh, |
2810 | struct smrq_slink *link, |
2811 | smrh_traits_t traits) |
2812 | { |
2813 | struct smrq_slink *first, *next; |
2814 | __smrq_slink_t *prev; |
2815 | smrsh_state_t state; |
2816 | hw_lck_ptr_t *head; |
2817 | uint32_t hash; |
2818 | |
2819 | state = os_atomic_load(&smrh->smrsh_state, dependency); |
2820 | hash = __smr_shash_hash(smrh, idx: state.curidx, link, traits); |
2821 | head = __smr_shash_bucket(smrh, state, sel: SMRSH_CUR, hash); |
2822 | first = hw_lck_ptr_lock(head, &smr_shash_grp); |
2823 | |
2824 | if (__improbable(first == SMRSH_MIGRATED)) { |
2825 | hw_lck_ptr_unlock_nopreempt(head, first, &smr_shash_grp); |
2826 | |
2827 | state = os_atomic_load(&smrh->smrsh_state, dependency); |
2828 | hash = __smr_shash_hash(smrh, idx: state.newidx, link, traits); |
2829 | head = __smr_shash_bucket(smrh, state, sel: SMRSH_NEW, hash); |
2830 | first = hw_lck_ptr_lock_nopreempt(head, &smr_shash_grp); |
2831 | } |
2832 | |
2833 | next = first; |
2834 | while (next != link) { |
2835 | if (__smr_shash_is_stop(link: next)) { |
2836 | __smr_shash_missing_elt_panic(smrh, link, traits); |
2837 | } |
2838 | prev = &next->next; |
2839 | next = smr_serialized_load(prev); |
2840 | } |
2841 | |
2842 | return (smr_shash_mut_cursor_t){ .head = head, .prev = prev }; |
2843 | } |
2844 | |
2845 | void |
2846 | __smr_shash_entered_mut_erase( |
2847 | struct smr_shash *smrh, |
2848 | smr_shash_mut_cursor_t cursor, |
2849 | struct smrq_slink *link, |
2850 | smrh_traits_t traits) |
2851 | { |
2852 | struct smrq_slink *next, *first; |
2853 | smrsh_state_t state; |
2854 | |
2855 | first = hw_lck_ptr_value(lck: cursor.head); |
2856 | |
2857 | next = smr_serialized_load(&link->next); |
2858 | if (first == link) { |
2859 | counter_dec_preemption_disabled(&smrh->smrsh_count); |
2860 | hw_lck_ptr_unlock(cursor.head, next, &smr_shash_grp); |
2861 | } else { |
2862 | smr_serialized_store_relaxed(cursor.prev, next); |
2863 | counter_dec_preemption_disabled(&smrh->smrsh_count); |
2864 | hw_lck_ptr_unlock(cursor.head, first, &smr_shash_grp); |
2865 | } |
2866 | |
2867 | state = atomic_load_explicit(&smrh->smrsh_state, memory_order_relaxed); |
2868 | if (first == link && __smr_shash_is_stop(link: next) && |
2869 | __smr_shash_should_shrink(smrh, state, count: __smr_shash_count(smrh))) { |
2870 | __smr_shash_schedule_rehash(smrh, traits, reason: SMRSH_REHASH_SHRINK); |
2871 | } |
2872 | } |
2873 | |
2874 | void |
2875 | __smr_shash_entered_mut_replace( |
2876 | smr_shash_mut_cursor_t cursor, |
2877 | struct smrq_slink *old_link, |
2878 | struct smrq_slink *new_link) |
2879 | { |
2880 | struct smrq_slink *first, *next; |
2881 | |
2882 | first = hw_lck_ptr_value(lck: cursor.head); |
2883 | |
2884 | next = smr_serialized_load(&old_link->next); |
2885 | smr_serialized_store_relaxed(&new_link->next, next); |
2886 | if (first == old_link) { |
2887 | hw_lck_ptr_unlock(cursor.head, new_link, &smr_shash_grp); |
2888 | } else { |
2889 | smr_serialized_store_relaxed(cursor.prev, new_link); |
2890 | hw_lck_ptr_unlock(cursor.head, first, &smr_shash_grp); |
2891 | } |
2892 | } |
2893 | |
2894 | void |
2895 | __smr_shash_entered_mut_abort(smr_shash_mut_cursor_t cursor) |
2896 | { |
2897 | hw_lck_ptr_unlock(cursor.head, |
2898 | hw_lck_ptr_value(cursor.head), &smr_shash_grp); |
2899 | } |
2900 | |
2901 | static kern_return_t |
2902 | __smr_shash_rehash_with_target( |
2903 | struct smr_shash *smrh, |
2904 | smrsh_state_t state, |
2905 | uint8_t newshift, |
2906 | smrh_traits_t traits) |
2907 | { |
2908 | const size_t FLAT_SIZE = 256; |
2909 | struct smrq_slink *flat_queue[FLAT_SIZE]; |
2910 | |
2911 | size_t oldsize, newsize; |
2912 | hw_lck_ptr_t *oldarray; |
2913 | hw_lck_ptr_t *newarray; |
2914 | uint32_t newseed; |
2915 | uint8_t oldidx; |
2916 | |
2917 | /* |
2918 | * This function resizes a scalable hash table. |
2919 | * |
2920 | * It doesn't require a lock because it is the callout |
2921 | * of a THREAD_CALL_ONCE thread call. |
2922 | */ |
2923 | |
2924 | oldidx = state.curidx; |
2925 | state.newidx = 1 - state.curidx; |
2926 | state.newshift = newshift; |
2927 | assert(__smr_shash_load_array(smrh, state.newidx) == NULL); |
2928 | |
2929 | oldsize = __smr_shash_cursize(state); |
2930 | newsize = __smr_shash_size_for_shift(shift: newshift); |
2931 | |
2932 | oldarray = __smr_shash_load_array(smrh, idx: state.curidx); |
2933 | newarray = (hw_lck_ptr_t *)smr_hash_alloc_array(size: newsize); |
2934 | newseed = (uint32_t)early_random(); |
2935 | |
2936 | if (newarray == NULL) { |
2937 | return KERN_RESOURCE_SHORTAGE; |
2938 | } |
2939 | |
2940 | /* |
2941 | * Step 1: initialize the new array and seed, |
2942 | * and then publish the state referencing it. |
2943 | * |
2944 | * We do not need to synchronize explicitly with SMR, |
2945 | * because readers/writers will notice rehashing when |
2946 | * the bucket they interact with has a SMRSH_MIGRATED |
2947 | * value. |
2948 | */ |
2949 | |
2950 | for (size_t i = 0; i < newsize; i++) { |
2951 | __smr_shash_bucket_init(head: &newarray[i]); |
2952 | } |
2953 | os_atomic_store(&smrh->smrsh_array[state.newidx], newarray, relaxed); |
2954 | os_atomic_store(&smrh->smrsh_seed[state.newidx], newseed, relaxed); |
2955 | os_atomic_store(&smrh->smrsh_state, state, release); |
2956 | |
2957 | /* |
2958 | * Step 2: migrate buckets "atomically" under the old bucket lock. |
2959 | * |
2960 | * This migration is atomic for writers because |
2961 | * they take the old bucket lock first, and if |
2962 | * they observe SMRSH_MIGRATED as the value, |
2963 | * go look in the new bucket instead. |
2964 | * |
2965 | * This migration is atomic for readers, because |
2966 | * as we move elements to their new buckets, |
2967 | * the hash chains will not circle back to their |
2968 | * bucket head (the "stop" value won't match), |
2969 | * or the bucket head will be SMRSH_MIGRATED. |
2970 | * |
2971 | * This causes a slowpath which spins waiting |
2972 | * for SMRSH_MIGRATED to appear and then looks |
2973 | * in the new bucket. |
2974 | */ |
2975 | for (size_t i = 0; i < oldsize; i++) { |
2976 | struct smrq_slink *first, *link, *next; |
2977 | hw_lck_ptr_t *head; |
2978 | uint32_t hash; |
2979 | size_t n = 0; |
2980 | |
2981 | link = first = hw_lck_ptr_lock(&oldarray[i], &smr_shash_grp); |
2982 | |
2983 | while (!__smr_shash_is_stop(link)) { |
2984 | flat_queue[n++ % FLAT_SIZE] = link; |
2985 | link = smr_serialized_load(&link->next); |
2986 | } |
2987 | |
2988 | while (n-- > 0) { |
2989 | for (size_t j = (n % FLAT_SIZE) + 1; j-- > 0;) { |
2990 | link = flat_queue[j]; |
2991 | hash = traits->obj_hash(link, newseed); |
2992 | head = &newarray[hash >> newshift]; |
2993 | next = hw_lck_ptr_lock_nopreempt(head, |
2994 | &smr_shash_grp); |
2995 | smr_serialized_store_relaxed(&link->next, next); |
2996 | hw_lck_ptr_unlock_nopreempt(head, link, |
2997 | &smr_shash_grp); |
2998 | } |
2999 | n &= ~(FLAT_SIZE - 1); |
3000 | |
3001 | /* |
3002 | * If there were more than FLAT_SIZE elements in the |
3003 | * chain (which is super unlikely and in many ways, |
3004 | * worrisome), then we need to repopoulate |
3005 | * the flattened queue array for each run. |
3006 | * |
3007 | * This is O(n^2) but we have worse problems anyway |
3008 | * if we ever hit this path. |
3009 | */ |
3010 | if (__improbable(n > 0)) { |
3011 | link = first; |
3012 | for (size_t j = 0; j < n - FLAT_SIZE; j++) { |
3013 | link = smr_serialized_load(&link->next); |
3014 | } |
3015 | |
3016 | flat_queue[0] = link; |
3017 | for (size_t j = 1; j < FLAT_SIZE; j++) { |
3018 | link = smr_serialized_load(&link->next); |
3019 | flat_queue[j] = link; |
3020 | } |
3021 | } |
3022 | } |
3023 | |
3024 | hw_lck_ptr_unlock(&oldarray[i], SMRSH_MIGRATED, &smr_shash_grp); |
3025 | } |
3026 | |
3027 | /* |
3028 | * Step 3: deallocate the old array of buckets, |
3029 | * making sure to hide it from readers. |
3030 | */ |
3031 | |
3032 | state.curshift = state.newshift; |
3033 | state.curidx = state.newidx; |
3034 | os_atomic_store(&smrh->smrsh_state, state, release); |
3035 | |
3036 | smr_synchronize(smr: traits->domain); |
3037 | |
3038 | os_atomic_store(&smrh->smrsh_array[oldidx], NULL, relaxed); |
3039 | for (size_t i = 0; i < oldsize; i++) { |
3040 | __smr_shash_bucket_destroy(head: &oldarray[i]); |
3041 | } |
3042 | smr_hash_free_array(array: (struct smrq_slist_head *)oldarray, size: oldsize); |
3043 | |
3044 | return KERN_SUCCESS; |
3045 | } |
3046 | |
3047 | static void |
3048 | __smr_shash_rehash(thread_call_param_t arg0, thread_call_param_t arg1) |
3049 | { |
3050 | struct smr_shash *smrh = arg0; |
3051 | smrh_traits_t traits = arg1; |
3052 | smrsh_rehash_t reason; |
3053 | smrsh_state_t state; |
3054 | uint64_t count; |
3055 | kern_return_t kr; |
3056 | |
3057 | do { |
3058 | reason = os_atomic_xchg(&smrh->smrsh_rehashing, |
3059 | SMRSH_REHASH_RUNNING, relaxed); |
3060 | |
3061 | state = os_atomic_load(&smrh->smrsh_state, relaxed); |
3062 | count = __smr_shash_count(smrh); |
3063 | |
3064 | if (__smr_shash_should_grow(smrh, state, count)) { |
3065 | kr = __smr_shash_rehash_with_target(smrh, state, |
3066 | newshift: state.curshift - 1, traits); |
3067 | } else if (__smr_shash_should_shrink(smrh, state, count)) { |
3068 | kr = __smr_shash_rehash_with_target(smrh, state, |
3069 | newshift: state.curshift + 1, traits); |
3070 | } else if (reason & SMRSH_REHASH_RESEED) { |
3071 | kr = __smr_shash_rehash_with_target(smrh, state, |
3072 | newshift: state.curshift, traits); |
3073 | } else { |
3074 | kr = KERN_SUCCESS; |
3075 | } |
3076 | |
3077 | if (kr == KERN_RESOURCE_SHORTAGE) { |
3078 | uint64_t deadline; |
3079 | |
3080 | os_atomic_or(&smrh->smrsh_rehashing, reason, relaxed); |
3081 | nanoseconds_to_deadline(NSEC_PER_MSEC, result: &deadline); |
3082 | thread_call_enter1_delayed(call: smrh->smrsh_callout, |
3083 | param1: arg1, deadline); |
3084 | break; |
3085 | } |
3086 | } while (!os_atomic_cmpxchg(&smrh->smrsh_rehashing, |
3087 | SMRSH_REHASH_RUNNING, SMRSH_REHASH_NONE, relaxed)); |
3088 | } |
3089 | |
3090 | void |
3091 | smr_shash_init(struct smr_shash *smrh, smrsh_policy_t policy, size_t min_size) |
3092 | { |
3093 | smrsh_state_t state; |
3094 | hw_lck_ptr_t *array; |
3095 | uint8_t shift; |
3096 | size_t size; |
3097 | |
3098 | switch (policy) { |
3099 | case SMRSH_COMPACT: |
3100 | if (min_size < 2) { |
3101 | min_size = 2; |
3102 | } |
3103 | break; |
3104 | default: |
3105 | if (min_size < 16) { |
3106 | min_size = 16; |
3107 | } |
3108 | break; |
3109 | } |
3110 | |
3111 | switch (policy) { |
3112 | case SMRSH_COMPACT: |
3113 | size = MIN(2, min_size); |
3114 | break; |
3115 | case SMRSH_BALANCED: |
3116 | case SMRSH_BALANCED_NOSHRINK: |
3117 | size = MIN(16, min_size); |
3118 | break; |
3119 | case SMRSH_FASTEST: |
3120 | size = min_size; |
3121 | break; |
3122 | } |
3123 | |
3124 | if (size > KALLOC_SAFE_ALLOC_SIZE / sizeof(*array)) { |
3125 | size = KALLOC_SAFE_ALLOC_SIZE / sizeof(*array); |
3126 | } |
3127 | shift = (uint8_t)__builtin_clz((uint32_t)(size - 1)); |
3128 | size = (~0u >> shift) + 1; |
3129 | array = (hw_lck_ptr_t *)smr_hash_alloc_array(size); |
3130 | for (size_t i = 0; i < size; i++) { |
3131 | __smr_shash_bucket_init(head: &array[i]); |
3132 | } |
3133 | |
3134 | state = (smrsh_state_t){ |
3135 | .curshift = shift, |
3136 | .newshift = shift, |
3137 | }; |
3138 | *smrh = (struct smr_shash){ |
3139 | .smrsh_array[0] = array, |
3140 | .smrsh_seed[0] = (uint32_t)early_random(), |
3141 | .smrsh_state = state, |
3142 | .smrsh_policy = policy, |
3143 | .smrsh_min_shift = (uint8_t)flsll(mask: min_size - 1), |
3144 | }; |
3145 | counter_alloc(&smrh->smrsh_count); |
3146 | smrh->smrsh_callout = thread_call_allocate_with_options(func: __smr_shash_rehash, |
3147 | param0: smrh, pri: THREAD_CALL_PRIORITY_KERNEL, options: THREAD_CALL_OPTIONS_ONCE); |
3148 | } |
3149 | |
3150 | void |
3151 | __smr_shash_destroy( |
3152 | struct smr_shash *smrh, |
3153 | smrh_traits_t traits, |
3154 | void (^free)(void *)) |
3155 | { |
3156 | smrsh_state_t state; |
3157 | hw_lck_ptr_t *array; |
3158 | size_t size; |
3159 | |
3160 | thread_call_cancel_wait(call: smrh->smrsh_callout); |
3161 | |
3162 | state = os_atomic_load(&smrh->smrsh_state, dependency); |
3163 | assert(state.curidx == state.newidx); |
3164 | assert(__smr_shash_load_array(smrh, 1 - state.curidx) == NULL); |
3165 | size = __smr_shash_cursize(state); |
3166 | array = __smr_shash_load_array(smrh, idx: state.curidx); |
3167 | |
3168 | if (free) { |
3169 | for (size_t i = 0; i < size; i++) { |
3170 | struct smrq_slink *link, *next; |
3171 | |
3172 | next = hw_lck_ptr_value(lck: &array[i]); |
3173 | while (!__smr_shash_is_stop(link: next)) { |
3174 | link = next; |
3175 | next = smr_serialized_load(&link->next); |
3176 | free(__smrht_link_to_obj(traits, link)); |
3177 | } |
3178 | } |
3179 | } |
3180 | for (size_t i = 0; i < size; i++) { |
3181 | __smr_shash_bucket_destroy(head: &array[i]); |
3182 | } |
3183 | |
3184 | thread_call_free(call: smrh->smrsh_callout); |
3185 | counter_free(&smrh->smrsh_count); |
3186 | smr_hash_free_array(array: (struct smrq_slist_head *)array, size); |
3187 | bzero(s: smrh, n: sizeof(*smrh)); |
3188 | } |
3189 | |
3190 | |
3191 | #pragma mark misc |
3192 | |
3193 | void |
3194 | __smr_linkage_invalid(__smrq_link_t *link) |
3195 | { |
3196 | struct smrq_link *elem = __container_of(link, struct smrq_link, next); |
3197 | struct smrq_link *next = smr_serialized_load(&elem->next); |
3198 | |
3199 | panic("Invalid queue linkage: elt:%p next:%p next->prev:%p" , |
3200 | elem, next, __container_of(next->prev, struct smrq_link, next)); |
3201 | } |
3202 | |
3203 | void |
3204 | __smr_stail_invalid(__smrq_slink_t *link, __smrq_slink_t *last) |
3205 | { |
3206 | struct smrq_slink *elem = __container_of(link, struct smrq_slink, next); |
3207 | struct smrq_slink *next = smr_serialized_load(&elem->next); |
3208 | |
3209 | if (next) { |
3210 | panic("Invalid queue tail (element past end): elt:%p elt->next:%p" , |
3211 | elem, next); |
3212 | } else { |
3213 | panic("Invalid queue tail (early end): elt:%p tail:%p" , |
3214 | elem, __container_of(last, struct smrq_slink, next)); |
3215 | } |
3216 | } |
3217 | |
3218 | void |
3219 | __smr_tail_invalid(__smrq_link_t *link, __smrq_link_t *last) |
3220 | { |
3221 | struct smrq_link *elem = __container_of(link, struct smrq_link, next); |
3222 | struct smrq_link *next = smr_serialized_load(&elem->next); |
3223 | |
3224 | if (next) { |
3225 | panic("Invalid queue tail (element past end): elt:%p elt->next:%p" , |
3226 | elem, next); |
3227 | } else { |
3228 | panic("Invalid queue tail (early end): elt:%p tail:%p" , |
3229 | elem, __container_of(last, struct smrq_link, next)); |
3230 | } |
3231 | } |
3232 | |