1 | /* |
2 | * Copyright (c) 2000-2007 Apple Computer, Inc. All rights reserved. |
3 | * |
4 | * @APPLE_OSREFERENCE_LICENSE_HEADER_START@ |
5 | * |
6 | * This file contains Original Code and/or Modifications of Original Code |
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14 | * |
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27 | */ |
28 | /* |
29 | * @OSF_COPYRIGHT@ |
30 | */ |
31 | /* |
32 | * Mach Operating System |
33 | * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University |
34 | * All Rights Reserved. |
35 | * |
36 | * Permission to use, copy, modify and distribute this software and its |
37 | * documentation is hereby granted, provided that both the copyright |
38 | * notice and this permission notice appear in all copies of the |
39 | * software, derivative works or modified versions, and any portions |
40 | * thereof, and that both notices appear in supporting documentation. |
41 | * |
42 | * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" |
43 | * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR |
44 | * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. |
45 | * |
46 | * Carnegie Mellon requests users of this software to return to |
47 | * |
48 | * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU |
49 | * School of Computer Science |
50 | * Carnegie Mellon University |
51 | * Pittsburgh PA 15213-3890 |
52 | * |
53 | * any improvements or extensions that they make and grant Carnegie Mellon |
54 | * the rights to redistribute these changes. |
55 | */ |
56 | /* |
57 | */ |
58 | /* |
59 | * Author: Avadis Tevanian, Jr. |
60 | * Date: 1986 |
61 | * |
62 | * Compute various averages. |
63 | */ |
64 | |
65 | #include <mach/mach_types.h> |
66 | |
67 | #include <kern/sched.h> |
68 | #include <kern/assert.h> |
69 | #include <kern/processor.h> |
70 | #include <kern/thread.h> |
71 | #if CONFIG_TELEMETRY |
72 | #include <kern/telemetry.h> |
73 | #endif |
74 | |
75 | #include <sys/kdebug.h> |
76 | |
77 | uint32_t avenrun[3] = {0, 0, 0}; |
78 | uint32_t mach_factor[3] = {0, 0, 0}; |
79 | |
80 | uint32_t sched_load_average, sched_mach_factor; |
81 | |
82 | #if defined(CONFIG_SCHED_TIMESHARE_CORE) |
83 | /* |
84 | * Values are scaled by LOAD_SCALE, defined in processor_info.h |
85 | */ |
86 | #define base(n) ((n) << SCHED_TICK_SHIFT) |
87 | #define frac(n) (((base(n) - 1) * LOAD_SCALE) / base(n)) |
88 | |
89 | static uint32_t fract[3] = { |
90 | frac(5), /* 5 second average */ |
91 | frac(30), /* 30 second average */ |
92 | frac(60), /* 1 minute average */ |
93 | }; |
94 | |
95 | #undef base |
96 | #undef frac |
97 | |
98 | #endif /* CONFIG_SCHED_TIMESHARE_CORE */ |
99 | |
100 | static unsigned int sched_nrun; |
101 | |
102 | typedef void (*sched_avg_comp_t)( |
103 | void *param); |
104 | |
105 | static struct sched_average { |
106 | sched_avg_comp_t comp; |
107 | void *param; |
108 | int period; /* in seconds */ |
109 | uint64_t deadline; |
110 | } sched_average[] = { |
111 | { compute_averunnable, &sched_nrun, 5, 0 }, |
112 | { compute_stack_target, NULL, 5, 1 }, |
113 | { compute_pageout_gc_throttle, NULL, 1, 0 }, |
114 | { compute_pmap_gc_throttle, NULL, 60, 0 }, |
115 | #if CONFIG_TELEMETRY |
116 | { compute_telemetry, NULL, 1, 0 }, |
117 | #endif |
118 | { NULL, NULL, 0, 0 } |
119 | }; |
120 | |
121 | typedef struct sched_average *sched_average_t; |
122 | |
123 | /* |
124 | * Scheduler load calculation algorithm |
125 | * |
126 | * The scheduler load values provide an estimate of the number of runnable |
127 | * timeshare threads in the system at various priority bands. The load |
128 | * ultimately affects the priority shifts applied to all threads in a band |
129 | * causing them to timeshare with other threads in the system. The load is |
130 | * maintained in buckets, with each bucket corresponding to a priority band. |
131 | * |
132 | * Each runnable thread on the system contributes its load to its priority |
133 | * band and to the bands above it. The contribution of a thread to the bands |
134 | * above it is not strictly 1:1 and is weighted based on the priority band |
135 | * of the thread. The rules of thread load contribution to each of its higher |
136 | * bands are as follows: |
137 | * |
138 | * - DF threads: Upto (2 * NCPUs) threads |
139 | * - UT threads: Upto NCPUs threads |
140 | * - BG threads: Upto 1 thread |
141 | * |
142 | * To calculate the load values, the various run buckets are sampled (every |
143 | * sched_load_compute_interval_abs) and the weighted contributions of the the |
144 | * lower bucket threads are added. The resultant value is plugged into an |
145 | * exponentially weighted moving average formula: |
146 | * new-load = alpha * old-load + (1 - alpha) * run-bucket-sample-count |
147 | * (where, alpha < 1) |
148 | * The calculations for the scheduler load are done using fixpoint math with |
149 | * a scale factor of 16 to avoid expensive divides and floating point |
150 | * operations. The final load values are a smooth curve representative of |
151 | * the actual number of runnable threads in a priority band. |
152 | */ |
153 | |
154 | /* Maintains the current (scaled for fixpoint) load in various buckets */ |
155 | uint32_t sched_load[TH_BUCKET_MAX]; |
156 | |
157 | /* |
158 | * Alpha factor for the EWMA alogrithm. The current values are chosen as |
159 | * 6:10 ("old load":"new samples") to make sure the scheduler reacts fast |
160 | * enough to changing system load but does not see too many spikes from bursty |
161 | * activity. The current values ensure that the scheduler would converge |
162 | * to the latest load in 2-3 sched_load_compute_interval_abs intervals |
163 | * (which amounts to ~30-45ms with current values). |
164 | */ |
165 | #define SCHED_LOAD_EWMA_ALPHA_OLD 6 |
166 | #define SCHED_LOAD_EWMA_ALPHA_NEW 10 |
167 | #define SCHED_LOAD_EWMA_ALPHA_SHIFT 4 |
168 | static_assert((SCHED_LOAD_EWMA_ALPHA_OLD + SCHED_LOAD_EWMA_ALPHA_NEW) == (1ul << SCHED_LOAD_EWMA_ALPHA_SHIFT)); |
169 | |
170 | /* For fixpoint EWMA, roundup the load to make it converge */ |
171 | #define SCHED_LOAD_EWMA_ROUNDUP(load) (((load) & (1ul << (SCHED_LOAD_EWMA_ALPHA_SHIFT - 1))) != 0) |
172 | |
173 | /* Macro to convert scaled sched load to a real load value */ |
174 | #define SCHED_LOAD_EWMA_UNSCALE(load) (((load) >> SCHED_LOAD_EWMA_ALPHA_SHIFT) + SCHED_LOAD_EWMA_ROUNDUP(load)) |
175 | |
176 | /* |
177 | * Routine to capture the latest runnable counts and update sched_load */ |
178 | void |
179 | compute_sched_load(void) |
180 | { |
181 | /* |
182 | * Retrieve a snapshot of the current run counts. |
183 | * |
184 | * Why not a bcopy()? Because we need atomic word-sized reads of sched_run_buckets, |
185 | * not byte-by-byte copy. |
186 | */ |
187 | uint32_t ncpus = processor_avail_count; |
188 | uint32_t load_now[TH_BUCKET_MAX]; |
189 | |
190 | load_now[TH_BUCKET_RUN] = sched_run_buckets[TH_BUCKET_RUN]; |
191 | load_now[TH_BUCKET_FIXPRI] = sched_run_buckets[TH_BUCKET_FIXPRI]; |
192 | load_now[TH_BUCKET_SHARE_FG] = sched_run_buckets[TH_BUCKET_SHARE_FG]; |
193 | load_now[TH_BUCKET_SHARE_DF] = sched_run_buckets[TH_BUCKET_SHARE_DF]; |
194 | load_now[TH_BUCKET_SHARE_UT] = sched_run_buckets[TH_BUCKET_SHARE_UT]; |
195 | load_now[TH_BUCKET_SHARE_BG] = sched_run_buckets[TH_BUCKET_SHARE_BG]; |
196 | |
197 | assert(load_now[TH_BUCKET_RUN] >= 0); |
198 | assert(load_now[TH_BUCKET_FIXPRI] >= 0); |
199 | |
200 | uint32_t nthreads = load_now[TH_BUCKET_RUN]; |
201 | uint32_t nfixpri = load_now[TH_BUCKET_FIXPRI]; |
202 | |
203 | KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE, |
204 | MACHDBG_CODE(DBG_MACH_SCHED, MACH_SCHED_LOAD) | DBG_FUNC_NONE, |
205 | load_now[TH_BUCKET_FIXPRI], (load_now[TH_BUCKET_SHARE_FG] + load_now[TH_BUCKET_SHARE_DF]), |
206 | load_now[TH_BUCKET_SHARE_BG], load_now[TH_BUCKET_SHARE_UT], 0); |
207 | |
208 | /* |
209 | * Compute the timeshare priority conversion factor based on loading. |
210 | * Because our counters may be incremented and accessed |
211 | * concurrently with respect to each other, we may have |
212 | * windows where the invariant (nthreads - nfixpri) == (fg + df + bg + ut) |
213 | * is broken, so truncate values in these cases. |
214 | */ |
215 | uint32_t timeshare_threads = (nthreads - nfixpri); |
216 | for (uint32_t i = TH_BUCKET_SHARE_FG; i <= TH_BUCKET_SHARE_BG ; i++) { |
217 | if (load_now[i] > timeshare_threads) |
218 | load_now[i] = timeshare_threads; |
219 | } |
220 | |
221 | /* |
222 | * Default threads contribute up to (NCPUS * 2) of load to FG threads |
223 | */ |
224 | if (load_now[TH_BUCKET_SHARE_DF] <= (ncpus * 2)) { |
225 | load_now[TH_BUCKET_SHARE_FG] += load_now[TH_BUCKET_SHARE_DF]; |
226 | } else { |
227 | load_now[TH_BUCKET_SHARE_FG] += (ncpus * 2); |
228 | } |
229 | |
230 | /* |
231 | * Utility threads contribute up to NCPUS of load to FG & DF threads |
232 | */ |
233 | if (load_now[TH_BUCKET_SHARE_UT] <= ncpus) { |
234 | load_now[TH_BUCKET_SHARE_FG] += load_now[TH_BUCKET_SHARE_UT]; |
235 | load_now[TH_BUCKET_SHARE_DF] += load_now[TH_BUCKET_SHARE_UT]; |
236 | } else { |
237 | load_now[TH_BUCKET_SHARE_FG] += ncpus; |
238 | load_now[TH_BUCKET_SHARE_DF] += ncpus; |
239 | } |
240 | |
241 | /* |
242 | * BG threads contribute up to 1 thread worth of load to FG, DF and UT threads |
243 | */ |
244 | if (load_now[TH_BUCKET_SHARE_BG] > 0) { |
245 | load_now[TH_BUCKET_SHARE_FG] += 1; |
246 | load_now[TH_BUCKET_SHARE_DF] += 1; |
247 | load_now[TH_BUCKET_SHARE_UT] += 1; |
248 | } |
249 | |
250 | /* |
251 | * The conversion factor consists of two components: |
252 | * a fixed value based on the absolute time unit (sched_fixed_shift), |
253 | * and a dynamic portion based on load (sched_load_shifts). |
254 | * |
255 | * Zero load results in a out of range shift count. |
256 | */ |
257 | |
258 | for (uint32_t i = TH_BUCKET_SHARE_FG; i <= TH_BUCKET_SHARE_BG ; i++) { |
259 | uint32_t bucket_load = 0; |
260 | |
261 | if (load_now[i] > ncpus) { |
262 | /* Normalize the load to number of CPUs */ |
263 | if (ncpus > 1) |
264 | bucket_load = load_now[i] / ncpus; |
265 | else |
266 | bucket_load = load_now[i]; |
267 | |
268 | if (bucket_load > MAX_LOAD) |
269 | bucket_load = MAX_LOAD; |
270 | } |
271 | /* Plug the load values into the EWMA algorithm to calculate (scaled for fixpoint) sched_load */ |
272 | sched_load[i] = (sched_load[i] * SCHED_LOAD_EWMA_ALPHA_OLD) + ((bucket_load << SCHED_LOAD_EWMA_ALPHA_SHIFT) * SCHED_LOAD_EWMA_ALPHA_NEW); |
273 | sched_load[i] = sched_load[i] >> SCHED_LOAD_EWMA_ALPHA_SHIFT; |
274 | } |
275 | |
276 | KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE, |
277 | MACHDBG_CODE(DBG_MACH_SCHED, MACH_SCHED_LOAD_EFFECTIVE) | DBG_FUNC_NONE, |
278 | SCHED_LOAD_EWMA_UNSCALE(sched_load[TH_BUCKET_SHARE_FG]), SCHED_LOAD_EWMA_UNSCALE(sched_load[TH_BUCKET_SHARE_DF]), |
279 | SCHED_LOAD_EWMA_UNSCALE(sched_load[TH_BUCKET_SHARE_UT]), SCHED_LOAD_EWMA_UNSCALE(sched_load[TH_BUCKET_SHARE_BG]), 0); |
280 | } |
281 | |
282 | void |
283 | compute_averages(uint64_t stdelta) |
284 | { |
285 | |
286 | uint32_t nthreads = sched_run_buckets[TH_BUCKET_RUN] - 1; |
287 | uint32_t ncpus = processor_avail_count; |
288 | |
289 | /* Update the global pri_shifts based on the latest values */ |
290 | for (uint32_t i = TH_BUCKET_SHARE_FG; i <= TH_BUCKET_SHARE_BG ; i++) { |
291 | uint32_t bucket_load = SCHED_LOAD_EWMA_UNSCALE(sched_load[i]); |
292 | sched_pri_shifts[i] = sched_fixed_shift - sched_load_shifts[bucket_load]; |
293 | } |
294 | |
295 | /* |
296 | * Sample total running threads for the load average calculation. |
297 | */ |
298 | sched_nrun = nthreads; |
299 | |
300 | /* |
301 | * Load average and mach factor calculations for |
302 | * those which ask about these things. |
303 | */ |
304 | uint32_t average_now = nthreads * LOAD_SCALE; |
305 | uint32_t factor_now; |
306 | |
307 | if (nthreads > ncpus) |
308 | factor_now = (ncpus * LOAD_SCALE) / (nthreads + 1); |
309 | else |
310 | factor_now = (ncpus - nthreads) * LOAD_SCALE; |
311 | |
312 | /* |
313 | * For those statistics that formerly relied on being recomputed |
314 | * on timer ticks, advance by the approximate number of corresponding |
315 | * elapsed intervals, thus compensating for potential idle intervals. |
316 | */ |
317 | for (uint32_t index = 0; index < stdelta; index++) { |
318 | sched_mach_factor = ((sched_mach_factor << 2) + factor_now) / 5; |
319 | sched_load_average = ((sched_load_average << 2) + average_now) / 5; |
320 | } |
321 | |
322 | /* |
323 | * Compute old-style Mach load averages. |
324 | */ |
325 | for (uint32_t index = 0; index < stdelta; index++) { |
326 | for (uint32_t i = 0; i < 3; i++) { |
327 | mach_factor[i] = ((mach_factor[i] * fract[i]) + |
328 | (factor_now * (LOAD_SCALE - fract[i]))) / LOAD_SCALE; |
329 | |
330 | avenrun[i] = ((avenrun[i] * fract[i]) + |
331 | (average_now * (LOAD_SCALE - fract[i]))) / LOAD_SCALE; |
332 | } |
333 | } |
334 | |
335 | /* |
336 | * Compute averages in other components. |
337 | */ |
338 | uint64_t abstime = mach_absolute_time(); |
339 | |
340 | for (sched_average_t avg = sched_average; avg->comp != NULL; ++avg) { |
341 | if (abstime >= avg->deadline) { |
342 | uint64_t period_abs = (avg->period * sched_one_second_interval); |
343 | uint64_t ninvokes = 1; |
344 | |
345 | ninvokes += (abstime - avg->deadline) / period_abs; |
346 | ninvokes = MIN(ninvokes, SCHED_TICK_MAX_DELTA); |
347 | |
348 | for (uint32_t index = 0; index < ninvokes; index++) { |
349 | (*avg->comp)(avg->param); |
350 | } |
351 | avg->deadline = abstime + period_abs; |
352 | } |
353 | } |
354 | } |
355 | |