1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
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12 *
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15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
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19 * CDDL HEADER END
20 */
21 /*
22 * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
23 * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
24 */
25
26 /*
27 * The System Duty Cycle (SDC) scheduling class
28 * --------------------------------------------
29 *
30 * Background
31 *
32 * Kernel threads in Solaris have traditionally not been large consumers
33 * of CPU time. They typically wake up, perform a small amount of
34 * work, then go back to sleep waiting for either a timeout or another
35 * signal. On the assumption that the small amount of work that they do
36 * is important for the behavior of the whole system, these threads are
37 * treated kindly by the dispatcher and the SYS scheduling class: they run
38 * without preemption from anything other than real-time and interrupt
39 * threads; when preempted, they are put at the front of the queue, so they
40 * generally do not migrate between CPUs; and they are allowed to stay
41 * running until they voluntarily give up the CPU.
42 *
43 * As Solaris has evolved, new workloads have emerged which require the
44 * kernel to perform significant amounts of CPU-intensive work. One
45 * example of such a workload is ZFS's transaction group sync processing.
46 * Each sync operation generates a large batch of I/Os, and each I/O
47 * may need to be compressed and/or checksummed before it is written to
48 * storage. The taskq threads which perform the compression and checksums
49 * will run nonstop as long as they have work to do; a large sync operation
50 * on a compression-heavy dataset can keep them busy for seconds on end.
51 * This causes human-time-scale dispatch latency bubbles for any other
52 * threads which have the misfortune to share a CPU with the taskq threads.
53 *
54 * The SDC scheduling class is a solution to this problem.
55 *
56 *
57 * Overview
58 *
59 * SDC is centered around the concept of a thread's duty cycle (DC):
60 *
61 * ONPROC time
62 * Duty Cycle = ----------------------
63 * ONPROC + Runnable time
64 *
65 * This is the ratio of the time that the thread spent running on a CPU
66 * divided by the time it spent running or trying to run. It is unaffected
67 * by any time the thread spent sleeping, stopped, etc.
68 *
69 * A thread joining the SDC class specifies a "target" DC that it wants
70 * to run at. To implement this policy, the routine sysdc_update() scans
71 * the list of active SDC threads every few ticks and uses each thread's
72 * microstate data to compute the actual duty cycle that that thread
73 * has experienced recently. If the thread is under its target DC, its
74 * priority is increased to the maximum available (sysdc_maxpri, which is
75 * 99 by default). If the thread is over its target DC, its priority is
76 * reduced to the minimum available (sysdc_minpri, 0 by default). This
77 * is a fairly primitive approach, in that it doesn't use any of the
78 * intermediate priorities, but it's not completely inappropriate. Even
79 * though threads in the SDC class might take a while to do their job, they
80 * are by some definition important if they're running inside the kernel,
81 * so it is reasonable that they should get to run at priority 99.
82 *
83 * If a thread is running when sysdc_update() calculates its actual duty
84 * cycle, and there are other threads of equal or greater priority on its
85 * CPU's dispatch queue, sysdc_update() preempts that thread. The thread
86 * acknowledges the preemption by calling sysdc_preempt(), which calls
87 * setbackdq(), which gives other threads with the same priority a chance
88 * to run. This creates a de facto time quantum for threads in the SDC
89 * scheduling class.
90 *
91 * An SDC thread which is assigned priority 0 can continue to run if
92 * nothing else needs to use the CPU that it's running on. Similarly, an
93 * SDC thread at priority 99 might not get to run as much as it wants to
94 * if there are other priority-99 or higher threads on its CPU. These
95 * situations would cause the thread to get ahead of or behind its target
96 * DC; the longer the situations lasted, the further ahead or behind the
97 * thread would get. Rather than condemning a thread to a lifetime of
98 * paying for its youthful indiscretions, SDC keeps "base" values for
99 * ONPROC and Runnable times in each thread's sysdc data, and updates these
100 * values periodically. The duty cycle is then computed using the elapsed
101 * amount of ONPROC and Runnable times since those base times.
102 *
103 * Since sysdc_update() scans SDC threads fairly frequently, it tries to
104 * keep the list of "active" threads small by pruning out threads which
105 * have been asleep for a brief time. They are not pruned immediately upon
106 * going to sleep, since some threads may bounce back and forth between
107 * sleeping and being runnable.
108 *
109 *
110 * Interfaces
111 *
112 * void sysdc_thread_enter(t, dc, flags)
113 *
114 * Moves a kernel thread from the SYS scheduling class to the
115 * SDC class. t must have an associated LWP (created by calling
116 * lwp_kernel_create()). The thread will have a target DC of dc.
117 * Flags should be either 0 or SYSDC_THREAD_BATCH. If
118 * SYSDC_THREAD_BATCH is specified, the thread is expected to be
119 * doing large amounts of processing.
120 *
121 *
122 * Complications
123 *
124 * - Run queue balancing
125 *
126 * The Solaris dispatcher is biased towards letting a thread run
127 * on the same CPU which it last ran on, if no more than 3 ticks
128 * (i.e. rechoose_interval) have passed since the thread last ran.
129 * This helps to preserve cache warmth. On the other hand, it also
130 * tries to keep the per-CPU run queues fairly balanced; if the CPU
131 * chosen for a runnable thread has a run queue which is three or
132 * more threads longer than a neighboring CPU's queue, the runnable
133 * thread is dispatched onto the neighboring CPU instead.
134 *
135 * These policies work well for some workloads, but not for many SDC
136 * threads. The taskq client of SDC, for example, has many discrete
137 * units of work to do. The work units are largely independent, so
138 * cache warmth is not an important consideration. It is important
139 * that the threads fan out quickly to different CPUs, since the
140 * amount of work these threads have to do (a few seconds worth at a
141 * time) doesn't leave much time to correct thread placement errors
142 * (i.e. two SDC threads being dispatched to the same CPU).
143 *
144 * To fix this, SDC uses the TS_RUNQMATCH flag introduced for FSS.
145 * This tells the dispatcher to keep neighboring run queues' lengths
146 * more evenly matched, which allows SDC threads to migrate more
147 * easily.
148 *
149 * - LWPs and system processes
150 *
151 * SDC can only be used for kernel threads. Since SDC uses microstate
152 * accounting data to compute each thread's actual duty cycle, all
153 * threads entering the SDC class must have associated LWPs (which
154 * store the microstate data). This means that the threads have to
155 * be associated with an SSYS process, i.e. one created by newproc().
156 * If the microstate accounting information is ever moved into the
157 * kthread_t, this restriction could be lifted.
158 *
159 * - Dealing with oversubscription
160 *
161 * Since SDC duty cycles are per-thread, it is possible that the
162 * aggregate requested duty cycle of all SDC threads in a processor
163 * set could be greater than the total CPU time available in that set.
164 * The FSS scheduling class has an analogous situation, which it deals
165 * with by reducing each thread's allotted CPU time proportionally.
166 * Since SDC doesn't need to be as precise as FSS, it uses a simpler
167 * solution to the oversubscription problem.
168 *
169 * sysdc_update() accumulates the amount of time that max-priority SDC
170 * threads have spent on-CPU in each processor set, and uses that sum
171 * to create an implied duty cycle for that processor set:
172 *
173 * accumulated CPU time
174 * pset DC = -----------------------------------
175 * (# CPUs) * time since last update
176 *
177 * If this implied duty cycle is above a maximum pset duty cycle (90%
178 * by default), sysdc_update() sets the priority of all SDC threads
179 * in that processor set to sysdc_minpri for a "break" period. After
180 * the break period, it waits for a "nobreak" period before trying to
181 * enforce the pset duty cycle limit again.
182 *
183 * - Processor sets
184 *
185 * As the above implies, SDC is processor set aware, but it does not
186 * currently allow threads to change processor sets while in the SDC
187 * class. Instead, those threads must join the desired processor set
188 * before entering SDC. [1]
189 *
190 * - Batch threads
191 *
192 * A thread joining the SDC class can specify the SDC_THREAD_BATCH
193 * flag. This flag currently has no effect, but marks threads which
194 * do bulk processing.
195 *
196 * - t_kpri_req
197 *
198 * The TS and FSS scheduling classes pay attention to t_kpri_req,
199 * which provides a simple form of priority inheritance for
200 * synchronization primitives (such as rwlocks held as READER) which
201 * cannot be traced to a unique thread. The SDC class does not honor
202 * t_kpri_req, for a few reasons:
203 *
204 * 1. t_kpri_req is notoriously inaccurate. A measure of its
205 * inaccuracy is that it needs to be cleared every time a thread
206 * returns to user mode, because it is frequently non-zero at that
207 * point. This can happen because "ownership" of synchronization
208 * primitives that use t_kpri_req can be silently handed off,
209 * leaving no opportunity to will the t_kpri_req inheritance.
210 *
211 * 2. Unlike in TS and FSS, threads in SDC *will* eventually run at
212 * kernel priority. This means that even if an SDC thread
213 * is holding a synchronization primitive and running at low
214 * priority, its priority will eventually be raised above 60,
215 * allowing it to drive on and release the resource.
216 *
217 * 3. The first consumer of SDC uses the taskq subsystem, which holds
218 * a reader lock for the duration of the task's execution. This
219 * would mean that SDC threads would never drop below kernel
220 * priority in practice, which defeats one of the purposes of SDC.
221 *
222 * - Why not FSS?
223 *
224 * It might seem that the existing FSS scheduling class could solve
225 * the problems that SDC is attempting to solve. FSS's more precise
226 * solution to the oversubscription problem would hardly cause
227 * trouble, as long as it performed well. SDC is implemented as
228 * a separate scheduling class for two main reasons: the initial
229 * consumer of SDC does not map well onto the "project" abstraction
230 * that is central to FSS, and FSS does not expect to run at kernel
231 * priorities.
232 *
233 *
234 * Tunables
235 *
236 * - sysdc_update_interval_msec: Number of milliseconds between
237 * consecutive thread priority updates.
238 *
239 * - sysdc_reset_interval_msec: Number of milliseconds between
240 * consecutive resets of a thread's base ONPROC and Runnable
241 * times.
242 *
243 * - sysdc_prune_interval_msec: Number of milliseconds of sleeping
244 * before a thread is pruned from the active list.
245 *
246 * - sysdc_max_pset_DC: Allowable percentage of a processor set's
247 * CPU time which SDC can give to its high-priority threads.
248 *
249 * - sysdc_break_msec: Number of milliseconds of "break" taken when
250 * sysdc_max_pset_DC is exceeded.
251 *
252 *
253 * Future work (in SDC and related subsystems)
254 *
255 * - Per-thread rechoose interval (0 for SDC)
256 *
257 * Allow each thread to specify its own rechoose interval. SDC
258 * threads would specify an interval of zero, which would rechoose
259 * the CPU with the lowest priority once per update.
260 *
261 * - Allow threads to change processor sets after joining the SDC class
262 *
263 * - Thread groups and per-group DC
264 *
265 * It might be nice to be able to specify a duty cycle which applies
266 * to a group of threads in aggregate.
267 *
268 * - Per-group DC callback to allow dynamic DC tuning
269 *
270 * Currently, DCs are assigned when the thread joins SDC. Some
271 * workloads could benefit from being able to tune their DC using
272 * subsystem-specific knowledge about the workload.
273 *
274 * - Finer-grained priority updates
275 *
276 * - More nuanced management of oversubscription
277 *
278 * - Moving other CPU-intensive threads into SDC
279 *
280 * - Move msacct data into kthread_t
281 *
282 * This would allow kernel threads without LWPs to join SDC.
283 *
284 *
285 * Footnotes
286 *
287 * [1] The details of doing so are left as an exercise for the reader.
288 */
289
290 #include <sys/types.h>
291 #include <sys/sysdc.h>
292 #include <sys/sysdc_impl.h>
293
294 #include <sys/class.h>
295 #include <sys/cmn_err.h>
296 #include <sys/cpuvar.h>
297 #include <sys/cpupart.h>
298 #include <sys/debug.h>
299 #include <sys/disp.h>
300 #include <sys/errno.h>
301 #include <sys/inline.h>
302 #include <sys/kmem.h>
303 #include <sys/modctl.h>
304 #include <sys/schedctl.h>
305 #include <sys/sdt.h>
306 #include <sys/sunddi.h>
307 #include <sys/sysmacros.h>
308 #include <sys/systm.h>
309 #include <sys/var.h>
310
311 /*
312 * Tunables - loaded into the internal state at module load time
313 */
314 uint_t sysdc_update_interval_msec = 20;
315 uint_t sysdc_reset_interval_msec = 400;
316 uint_t sysdc_prune_interval_msec = 100;
317 uint_t sysdc_max_pset_DC = 90;
318 uint_t sysdc_break_msec = 80;
319
320 /*
321 * Internal state - constants set up by sysdc_initparam()
322 */
323 static clock_t sysdc_update_ticks; /* ticks between updates */
324 static uint_t sysdc_prune_updates; /* updates asleep before pruning */
325 static uint_t sysdc_reset_updates; /* # of updates before reset */
326 static uint_t sysdc_break_updates; /* updates to break */
327 static uint_t sysdc_nobreak_updates; /* updates to not check */
328 static uint_t sysdc_minDC; /* minimum allowed DC */
329 static uint_t sysdc_maxDC; /* maximum allowed DC */
330 static pri_t sysdc_minpri; /* minimum allowed priority */
331 static pri_t sysdc_maxpri; /* maximum allowed priority */
332
333 /*
334 * Internal state
335 */
336 static kmutex_t sysdc_pset_lock; /* lock protecting pset data */
337 static list_t sysdc_psets; /* list of psets with SDC threads */
338 static uint_t sysdc_param_init; /* sysdc_initparam() has been called */
339 static uint_t sysdc_update_timeout_started; /* update timeout is active */
340 static hrtime_t sysdc_last_update; /* time of last sysdc_update() */
341 static sysdc_t sysdc_dummy; /* used to terminate active lists */
342
343 /*
344 * Internal state - active hash table
345 */
346 #define SYSDC_NLISTS 8
347 #define SYSDC_HASH(sdc) (((uintptr_t)(sdc) >> 6) & (SYSDC_NLISTS - 1))
348 static sysdc_list_t sysdc_active[SYSDC_NLISTS];
349 #define SYSDC_LIST(sdc) (&sysdc_active[SYSDC_HASH(sdc)])
350
351 #ifdef DEBUG
352 static struct {
353 uint64_t sysdc_update_times_asleep;
354 uint64_t sysdc_update_times_base_ran_backwards;
355 uint64_t sysdc_update_times_already_done;
356 uint64_t sysdc_update_times_cur_ran_backwards;
357 uint64_t sysdc_compute_pri_breaking;
358 uint64_t sysdc_activate_enter;
359 uint64_t sysdc_update_enter;
360 uint64_t sysdc_update_exited;
361 uint64_t sysdc_update_not_sdc;
362 uint64_t sysdc_update_idle;
363 uint64_t sysdc_update_take_break;
364 uint64_t sysdc_update_no_psets;
365 uint64_t sysdc_tick_not_sdc;
366 uint64_t sysdc_tick_quantum_expired;
367 uint64_t sysdc_thread_enter_enter;
368 } sysdc_stats;
369
370 #define SYSDC_INC_STAT(x) (sysdc_stats.x++)
371 #else
372 #define SYSDC_INC_STAT(x) ((void)0)
373 #endif
374
375 /* macros are UPPER CASE */
376 #define HOWMANY(a, b) howmany((a), (b))
377 #define MSECTOTICKS(a) HOWMANY((a) * 1000, usec_per_tick)
378
379 static void
380 sysdc_initparam(void)
381 {
382 uint_t sysdc_break_ticks;
383
384 /* update / prune intervals */
385 sysdc_update_ticks = MSECTOTICKS(sysdc_update_interval_msec);
386
387 sysdc_prune_updates = HOWMANY(sysdc_prune_interval_msec,
388 sysdc_update_interval_msec);
389 sysdc_reset_updates = HOWMANY(sysdc_reset_interval_msec,
390 sysdc_update_interval_msec);
391
392 /* We must get at least a little time on CPU. */
393 sysdc_minDC = 1;
394 sysdc_maxDC = SYSDC_DC_MAX;
395 sysdc_minpri = 0;
396 sysdc_maxpri = maxclsyspri - 1;
397
398 /* break parameters */
399 if (sysdc_max_pset_DC > SYSDC_DC_MAX) {
400 sysdc_max_pset_DC = SYSDC_DC_MAX;
401 }
402 sysdc_break_ticks = MSECTOTICKS(sysdc_break_msec);
403 sysdc_break_updates = HOWMANY(sysdc_break_ticks, sysdc_update_ticks);
404
405 /*
406 * We want:
407 *
408 * sysdc_max_pset_DC = (nobreak / (break + nobreak))
409 *
410 * ==> nobreak = sysdc_max_pset_DC * (break + nobreak)
411 *
412 * sysdc_max_pset_DC * break
413 * ==> nobreak = -------------------------
414 * 1 - sysdc_max_pset_DC
415 */
416 sysdc_nobreak_updates =
417 HOWMANY((uint64_t)sysdc_break_updates * sysdc_max_pset_DC,
418 (SYSDC_DC_MAX - sysdc_max_pset_DC));
419
420 sysdc_param_init = 1;
421 }
422
423 #undef HOWMANY
424 #undef MSECTOTICKS
425
426 #define SDC_UPDATE_INITIAL 0x1 /* for the initial update */
427 #define SDC_UPDATE_TIMEOUT 0x2 /* from sysdc_update() */
428 #define SDC_UPDATE_TICK 0x4 /* from sysdc_tick(), on expiry */
429
430 /*
431 * Updates the recorded times in the sdc, and returns the elapsed ONPROC
432 * and Runnable times since the last reset.
433 *
434 * newO is the thread's actual ONPROC time; it's used during sysdc_update()
435 * to track processor set usage.
436 */
437 static void
438 sysdc_update_times(sysdc_t *sdc, uint_t flags,
439 hrtime_t *O, hrtime_t *R, hrtime_t *newO)
440 {
441 kthread_t *const t = sdc->sdc_thread;
442 const uint_t initial = (flags & SDC_UPDATE_INITIAL);
443 const uint_t update = (flags & SDC_UPDATE_TIMEOUT);
444 const clock_t now = ddi_get_lbolt();
445 uint_t do_reset;
446
447 ASSERT(THREAD_LOCK_HELD(t));
448
449 *O = *R = 0;
450
451 /* If we've been sleeping, we know we haven't had any ONPROC time. */
452 if (sdc->sdc_sleep_updates != 0 &&
453 sdc->sdc_sleep_updates != sdc->sdc_nupdates) {
454 *newO = sdc->sdc_last_base_O;
455 SYSDC_INC_STAT(sysdc_update_times_asleep);
456 return;
457 }
458
459 /*
460 * If this is our first update, or we've hit the reset point,
461 * we need to reset our base_{O,R}. Once we've updated them, we
462 * report O and R for the entire prior interval.
463 */
464 do_reset = initial;
465 if (update) {
466 ++sdc->sdc_nupdates;
467 if ((sdc->sdc_nupdates % sysdc_reset_updates) == 0)
468 do_reset = 1;
469 }
470 if (do_reset) {
471 hrtime_t baseO, baseR;
472 if (initial) {
473 /*
474 * Start off our cycle count somewhere in the middle,
475 * to keep the resets from all happening at once.
476 *
477 * 4999 is a handy prime much larger than
478 * sysdc_reset_updates, so that we don't run into
479 * trouble if the resolution is a multiple of
480 * sysdc_reset_updates.
481 */
482 sdc->sdc_nupdates = (uint_t)((gethrtime() % 4999) %
483 sysdc_reset_updates);
484 baseO = baseR = 0;
485 } else {
486 baseO = sdc->sdc_base_O;
487 baseR = sdc->sdc_base_R;
488 }
489
490 mstate_systhread_times(t, &sdc->sdc_base_O, &sdc->sdc_base_R);
491 *newO = sdc->sdc_base_O;
492
493 sdc->sdc_reset = now;
494 sdc->sdc_pri_check = -1; /* force mismatch below */
495
496 /*
497 * See below for rationale.
498 */
499 if (baseO > sdc->sdc_base_O || baseR > sdc->sdc_base_R) {
500 SYSDC_INC_STAT(sysdc_update_times_base_ran_backwards);
501 baseO = sdc->sdc_base_O;
502 baseR = sdc->sdc_base_R;
503 }
504
505 /* compute based on the entire interval */
506 *O = (sdc->sdc_base_O - baseO);
507 *R = (sdc->sdc_base_R - baseR);
508 return;
509 }
510
511 /*
512 * If we're called from sysdc_update(), we *must* return a value
513 * for newO, so we always call mstate_systhread_times().
514 *
515 * Otherwise, if we've already done a pri check this tick,
516 * we can skip it.
517 */
518 if (!update && sdc->sdc_pri_check == now) {
519 SYSDC_INC_STAT(sysdc_update_times_already_done);
520 return;
521 }
522
523 /* Get the current times from the thread */
524 sdc->sdc_pri_check = now;
525 mstate_systhread_times(t, &sdc->sdc_cur_O, &sdc->sdc_cur_R);
526 *newO = sdc->sdc_cur_O;
527
528 /*
529 * The updating of microstate accounting is not done under a
530 * consistent set of locks, particularly the t_waitrq field. This
531 * can lead to narrow windows in which we account for time in the
532 * wrong bucket, which on the next read will be accounted for
533 * correctly.
534 *
535 * If our sdc_base_* fields were affected by one of these blips, we
536 * throw away the old data, and pretend this tick didn't happen.
537 */
538 if (sdc->sdc_cur_O < sdc->sdc_base_O ||
539 sdc->sdc_cur_R < sdc->sdc_base_R) {
540
541 sdc->sdc_base_O = sdc->sdc_cur_O;
542 sdc->sdc_base_R = sdc->sdc_cur_R;
543
544 SYSDC_INC_STAT(sysdc_update_times_cur_ran_backwards);
545 return;
546 }
547
548 *O = sdc->sdc_cur_O - sdc->sdc_base_O;
549 *R = sdc->sdc_cur_R - sdc->sdc_base_R;
550 }
551
552 /*
553 * sysdc_compute_pri()
554 *
555 * Recomputes the priority of the thread, leaving the result in
556 * sdc->sdc_epri. Returns 1 if a priority update should occur
557 * (which will also trigger a cpu_surrender()), otherwise
558 * returns 0.
559 */
560 static uint_t
561 sysdc_compute_pri(sysdc_t *sdc, uint_t flags)
562 {
563 kthread_t *const t = sdc->sdc_thread;
564 const uint_t update = (flags & SDC_UPDATE_TIMEOUT);
565 const uint_t tick = (flags & SDC_UPDATE_TICK);
566
567 hrtime_t O, R;
568 hrtime_t newO = -1;
569
570 ASSERT(THREAD_LOCK_HELD(t));
571
572 sysdc_update_times(sdc, flags, &O, &R, &newO);
573 ASSERT(!update || newO != -1);
574
575 /* If we have new data, recompute our priority. */
576 if ((O + R) != 0) {
577 sdc->sdc_cur_DC = (O * SYSDC_DC_MAX) / (O + R);
578
579 /* Adjust our priority to move our DC closer to the target. */
580 if (sdc->sdc_cur_DC < sdc->sdc_target_DC)
581 sdc->sdc_pri = sdc->sdc_maxpri;
582 else
583 sdc->sdc_pri = sdc->sdc_minpri;
584 }
585
586 /*
587 * If our per-pset duty cycle goes over the max, we will take a break.
588 * This forces all sysdc threads in the pset to minimum priority, in
589 * order to let everyone else have a chance at the CPU.
590 */
591 if (sdc->sdc_pset->sdp_need_break) {
592 SYSDC_INC_STAT(sysdc_compute_pri_breaking);
593 sdc->sdc_epri = sdc->sdc_minpri;
594 } else {
595 sdc->sdc_epri = sdc->sdc_pri;
596 }
597
598 DTRACE_PROBE4(sysdc__compute__pri,
599 kthread_t *, t, pri_t, sdc->sdc_epri, uint_t, sdc->sdc_cur_DC,
600 uint_t, sdc->sdc_target_DC);
601
602 /*
603 * For sysdc_update(), we compute the ONPROC time for high-priority
604 * threads, which is used to calculate the per-pset duty cycle. We
605 * will always tell our callers to update the thread's priority,
606 * since we want to force a cpu_surrender().
607 *
608 * We reset sdc_update_ticks so that sysdc_tick() will only update
609 * the thread's priority if our timeout is delayed by a tick or
610 * more.
611 */
612 if (update) {
613 /* SDC threads are not allowed to change cpupart bindings. */
614 ASSERT(t->t_cpupart == sdc->sdc_pset->sdp_cpupart);
615
616 /* If we were at MAXPRI, account for our onproc time. */
617 if (t->t_pri == sdc->sdc_maxpri &&
618 sdc->sdc_last_base_O != 0 &&
619 sdc->sdc_last_base_O < newO) {
620 sdc->sdc_last_O = newO - sdc->sdc_last_base_O;
621 sdc->sdc_pset->sdp_onproc_time +=
622 (uint64_t)sdc->sdc_last_O;
623 sdc->sdc_pset->sdp_onproc_threads++;
624 } else {
625 sdc->sdc_last_O = 0;
626 }
627 sdc->sdc_last_base_O = newO;
628
629 sdc->sdc_update_ticks = sdc->sdc_ticks + sysdc_update_ticks + 1;
630 return (1);
631 }
632
633 /*
634 * Like sysdc_update(), sysdc_tick() always wants to update the
635 * thread's priority, so that the CPU is surrendered if necessary.
636 * We reset sdc_update_ticks so that if the timeout continues to be
637 * delayed, we'll update at the regular interval.
638 */
639 if (tick) {
640 ASSERT(sdc->sdc_ticks == sdc->sdc_update_ticks);
641 sdc->sdc_update_ticks = sdc->sdc_ticks + sysdc_update_ticks;
642 return (1);
643 }
644
645 /*
646 * Otherwise, only tell our callers to update the priority if it has
647 * changed.
648 */
649 return (sdc->sdc_epri != t->t_pri);
650 }
651
652 static void
653 sysdc_update_pri(sysdc_t *sdc, uint_t flags)
654 {
655 kthread_t *t = sdc->sdc_thread;
656
657 ASSERT(THREAD_LOCK_HELD(t));
658
659 if (sysdc_compute_pri(sdc, flags)) {
660 if (!thread_change_pri(t, sdc->sdc_epri, 0)) {
661 cpu_surrender(t);
662 }
663 }
664 }
665
666 /*
667 * Add a thread onto the active list. It will only be removed by
668 * sysdc_update().
669 */
670 static void
671 sysdc_activate(sysdc_t *sdc)
672 {
673 sysdc_t *volatile *headp = &SYSDC_LIST(sdc)->sdl_list;
674 sysdc_t *head;
675 kthread_t *t = sdc->sdc_thread;
676
677 SYSDC_INC_STAT(sysdc_activate_enter);
678
679 ASSERT(sdc->sdc_next == NULL);
680 ASSERT(THREAD_LOCK_HELD(t));
681
682 do {
683 head = *headp;
684 sdc->sdc_next = head;
685 } while (atomic_cas_ptr(headp, head, sdc) != head);
686 }
687
688 /*
689 * sysdc_update() has two jobs:
690 *
691 * 1. It updates the priorities of all active SDC threads on the system.
692 * 2. It measures pset CPU usage and enforces sysdc_max_pset_DC.
693 */
694 static void
695 sysdc_update(void *arg)
696 {
697 int idx;
698 sysdc_t *freelist = NULL;
699 sysdc_pset_t *cur;
700 hrtime_t now, diff;
701 uint_t redeploy = 1;
702
703 SYSDC_INC_STAT(sysdc_update_enter);
704
705 ASSERT(sysdc_update_timeout_started);
706
707 /*
708 * If this is our first time through, diff will be gigantic, and
709 * no breaks will be necessary.
710 */
711 now = gethrtime();
712 diff = now - sysdc_last_update;
713 sysdc_last_update = now;
714
715 mutex_enter(&sysdc_pset_lock);
716 for (cur = list_head(&sysdc_psets); cur != NULL;
717 cur = list_next(&sysdc_psets, cur)) {
718 boolean_t breaking = (cur->sdp_should_break != 0);
719
720 if (cur->sdp_need_break != breaking) {
721 DTRACE_PROBE2(sdc__pset__break, sysdc_pset_t *, cur,
722 boolean_t, breaking);
723 }
724 cur->sdp_onproc_time = 0;
725 cur->sdp_onproc_threads = 0;
726 cur->sdp_need_break = breaking;
727 }
728 mutex_exit(&sysdc_pset_lock);
729
730 for (idx = 0; idx < SYSDC_NLISTS; idx++) {
731 sysdc_list_t *sdl = &sysdc_active[idx];
732 sysdc_t *volatile *headp = &sdl->sdl_list;
733 sysdc_t *head, *tail;
734 sysdc_t **prevptr;
735
736 if (*headp == &sysdc_dummy)
737 continue;
738
739 /* Prevent any threads from exiting while we're poking them. */
740 mutex_enter(&sdl->sdl_lock);
741
742 /*
743 * Each sdl_list contains a singly-linked list of active
744 * threads. Threads which become active while we are
745 * processing the list will be added to sdl_list. Since we
746 * don't want that to interfere with our own processing, we
747 * swap in an empty list. Any newly active threads will
748 * go on to this empty list. When finished, we'll put any
749 * such threads at the end of the processed list.
750 */
751 head = atomic_swap_ptr(headp, &sysdc_dummy);
752 prevptr = &head;
753 while (*prevptr != &sysdc_dummy) {
754 sysdc_t *const sdc = *prevptr;
755 kthread_t *const t = sdc->sdc_thread;
756
757 /*
758 * If the thread has exited, move its sysdc_t onto
759 * freelist, to be freed later.
760 */
761 if (t == NULL) {
762 *prevptr = sdc->sdc_next;
763 SYSDC_INC_STAT(sysdc_update_exited);
764 sdc->sdc_next = freelist;
765 freelist = sdc;
766 continue;
767 }
768
769 thread_lock(t);
770 if (t->t_cid != sysdccid) {
771 thread_unlock(t);
772 prevptr = &sdc->sdc_next;
773 SYSDC_INC_STAT(sysdc_update_not_sdc);
774 continue;
775 }
776 ASSERT(t->t_cldata == sdc);
777
778 /*
779 * If the thread has been sleeping for longer
780 * than sysdc_prune_interval, make it inactive by
781 * removing it from the list.
782 */
783 if (!(t->t_state & (TS_RUN | TS_ONPROC)) &&
784 sdc->sdc_sleep_updates != 0 &&
785 (sdc->sdc_sleep_updates - sdc->sdc_nupdates) >
786 sysdc_prune_updates) {
787 *prevptr = sdc->sdc_next;
788 SYSDC_INC_STAT(sysdc_update_idle);
789 sdc->sdc_next = NULL;
790 thread_unlock(t);
791 continue;
792 }
793 sysdc_update_pri(sdc, SDC_UPDATE_TIMEOUT);
794 thread_unlock(t);
795
796 prevptr = &sdc->sdc_next;
797 }
798
799 /*
800 * Add our list to the bucket, putting any new entries
801 * added while we were working at the tail of the list.
802 */
803 do {
804 tail = *headp;
805 *prevptr = tail;
806 } while (atomic_cas_ptr(headp, tail, head) != tail);
807
808 mutex_exit(&sdl->sdl_lock);
809 }
810
811 mutex_enter(&sysdc_pset_lock);
812 for (cur = list_head(&sysdc_psets); cur != NULL;
813 cur = list_next(&sysdc_psets, cur)) {
814
815 cur->sdp_vtime_last_interval =
816 diff * cur->sdp_cpupart->cp_ncpus;
817 cur->sdp_DC_last_interval =
818 (cur->sdp_onproc_time * SYSDC_DC_MAX) /
819 cur->sdp_vtime_last_interval;
820
821 if (cur->sdp_should_break > 0) {
822 cur->sdp_should_break--; /* breaking */
823 continue;
824 }
825 if (cur->sdp_dont_break > 0) {
826 cur->sdp_dont_break--; /* waiting before checking */
827 continue;
828 }
829 if (cur->sdp_DC_last_interval > sysdc_max_pset_DC) {
830 cur->sdp_should_break = sysdc_break_updates;
831 cur->sdp_dont_break = sysdc_nobreak_updates;
832 SYSDC_INC_STAT(sysdc_update_take_break);
833 }
834 }
835
836 /*
837 * If there are no sysdc_psets, there can be no threads, so
838 * we can stop doing our timeout. Since we're holding the
839 * sysdc_pset_lock, no new sysdc_psets can come in, which will
840 * prevent anyone from racing with this and dropping our timeout
841 * on the floor.
842 */
843 if (list_is_empty(&sysdc_psets)) {
844 SYSDC_INC_STAT(sysdc_update_no_psets);
845 ASSERT(sysdc_update_timeout_started);
846 sysdc_update_timeout_started = 0;
847
848 redeploy = 0;
849 }
850 mutex_exit(&sysdc_pset_lock);
851
852 while (freelist != NULL) {
853 sysdc_t *cur = freelist;
854 freelist = cur->sdc_next;
855 kmem_free(cur, sizeof (*cur));
856 }
857
858 if (redeploy) {
859 (void) timeout(sysdc_update, arg, sysdc_update_ticks);
860 }
861 }
862
863 static void
864 sysdc_preempt(kthread_t *t)
865 {
866 ASSERT(t == curthread);
867 ASSERT(THREAD_LOCK_HELD(t));
868
869 setbackdq(t); /* give others a chance to run */
870 }
871
872 static void
873 sysdc_tick(kthread_t *t)
874 {
875 sysdc_t *sdc;
876
877 thread_lock(t);
878 if (t->t_cid != sysdccid) {
879 SYSDC_INC_STAT(sysdc_tick_not_sdc);
880 thread_unlock(t);
881 return;
882 }
883 sdc = t->t_cldata;
884 if (t->t_state == TS_ONPROC &&
885 t->t_pri < t->t_disp_queue->disp_maxrunpri) {
886 cpu_surrender(t);
887 }
888
889 if (t->t_state == TS_ONPROC || t->t_state == TS_RUN) {
890 ASSERT(sdc->sdc_sleep_updates == 0);
891 }
892
893 ASSERT(sdc->sdc_ticks != sdc->sdc_update_ticks);
894 sdc->sdc_ticks++;
895 if (sdc->sdc_ticks == sdc->sdc_update_ticks) {
896 SYSDC_INC_STAT(sysdc_tick_quantum_expired);
897 sysdc_update_pri(sdc, SDC_UPDATE_TICK);
898 ASSERT(sdc->sdc_ticks != sdc->sdc_update_ticks);
899 }
900 thread_unlock(t);
901 }
902
903 static void
904 sysdc_setrun(kthread_t *t)
905 {
906 sysdc_t *sdc = t->t_cldata;
907
908 ASSERT(THREAD_LOCK_HELD(t)); /* t should be in transition */
909
910 sdc->sdc_sleep_updates = 0;
911
912 if (sdc->sdc_next == NULL) {
913 /*
914 * Since we're in transition, we don't want to use the
915 * full thread_update_pri().
916 */
917 if (sysdc_compute_pri(sdc, 0)) {
918 THREAD_CHANGE_PRI(t, sdc->sdc_epri);
919 }
920 sysdc_activate(sdc);
921
922 ASSERT(sdc->sdc_next != NULL);
923 }
924
925 setbackdq(t);
926 }
927
928 static void
929 sysdc_wakeup(kthread_t *t)
930 {
931 sysdc_setrun(t);
932 }
933
934 static void
935 sysdc_sleep(kthread_t *t)
936 {
937 sysdc_t *sdc = t->t_cldata;
938
939 ASSERT(THREAD_LOCK_HELD(t)); /* t should be in transition */
940
941 sdc->sdc_sleep_updates = sdc->sdc_nupdates;
942 }
943
944 /*ARGSUSED*/
945 static int
946 sysdc_enterclass(kthread_t *t, id_t cid, void *parmsp, cred_t *reqpcredp,
947 void *bufp)
948 {
949 cpupart_t *const cpupart = t->t_cpupart;
950 sysdc_t *sdc = bufp;
951 sysdc_params_t *sdpp = parmsp;
952 sysdc_pset_t *newpset = sdc->sdc_pset;
953 sysdc_pset_t *pset;
954 int start_timeout;
955
956 if (t->t_cid != syscid)
957 return (EPERM);
958
959 ASSERT(ttolwp(t) != NULL);
960 ASSERT(sdpp != NULL);
961 ASSERT(newpset != NULL);
962 ASSERT(sysdc_param_init);
963
964 ASSERT(sdpp->sdp_minpri >= sysdc_minpri);
965 ASSERT(sdpp->sdp_maxpri <= sysdc_maxpri);
966 ASSERT(sdpp->sdp_DC >= sysdc_minDC);
967 ASSERT(sdpp->sdp_DC <= sysdc_maxDC);
968
969 sdc->sdc_thread = t;
970 sdc->sdc_pri = sdpp->sdp_maxpri; /* start off maximally */
971 sdc->sdc_minpri = sdpp->sdp_minpri;
972 sdc->sdc_maxpri = sdpp->sdp_maxpri;
973 sdc->sdc_target_DC = sdpp->sdp_DC;
974 sdc->sdc_ticks = 0;
975 sdc->sdc_update_ticks = sysdc_update_ticks + 1;
976
977 /* Assign ourselves to the appropriate pset. */
978 sdc->sdc_pset = NULL;
979 mutex_enter(&sysdc_pset_lock);
980 for (pset = list_head(&sysdc_psets); pset != NULL;
981 pset = list_next(&sysdc_psets, pset)) {
982 if (pset->sdp_cpupart == cpupart) {
983 break;
984 }
985 }
986 if (pset == NULL) {
987 pset = newpset;
988 newpset = NULL;
989 pset->sdp_cpupart = cpupart;
990 list_insert_tail(&sysdc_psets, pset);
991 }
992 pset->sdp_nthreads++;
993 ASSERT(pset->sdp_nthreads > 0);
994
995 sdc->sdc_pset = pset;
996
997 start_timeout = (sysdc_update_timeout_started == 0);
998 sysdc_update_timeout_started = 1;
999 mutex_exit(&sysdc_pset_lock);
1000
1001 if (newpset != NULL)
1002 kmem_free(newpset, sizeof (*newpset));
1003
1004 /* Update t's scheduling class and priority. */
1005 thread_lock(t);
1006 t->t_clfuncs = &(sclass[cid].cl_funcs->thread);
1007 t->t_cid = cid;
1008 t->t_cldata = sdc;
1009 t->t_schedflag |= TS_RUNQMATCH;
1010
1011 sysdc_update_pri(sdc, SDC_UPDATE_INITIAL);
1012 thread_unlock(t);
1013
1014 /* Kick off the thread timeout if we're the first one in. */
1015 if (start_timeout) {
1016 (void) timeout(sysdc_update, NULL, sysdc_update_ticks);
1017 }
1018
1019 return (0);
1020 }
1021
1022 static void
1023 sysdc_leave(sysdc_t *sdc)
1024 {
1025 sysdc_pset_t *sdp = sdc->sdc_pset;
1026 sysdc_list_t *sdl = SYSDC_LIST(sdc);
1027 uint_t freedc;
1028
1029 mutex_enter(&sdl->sdl_lock); /* block sysdc_update() */
1030 sdc->sdc_thread = NULL;
1031 freedc = (sdc->sdc_next == NULL);
1032 mutex_exit(&sdl->sdl_lock);
1033
1034 mutex_enter(&sysdc_pset_lock);
1035 ASSERT(sdp != NULL);
1036 ASSERT(sdp->sdp_nthreads > 0);
1037 --sdp->sdp_nthreads;
1038 if (sdp->sdp_nthreads == 0) {
1039 list_remove(&sysdc_psets, sdp);
1040 } else {
1041 sdp = NULL;
1042 }
1043 mutex_exit(&sysdc_pset_lock);
1044
1045 if (freedc)
1046 kmem_free(sdc, sizeof (*sdc));
1047 if (sdp != NULL)
1048 kmem_free(sdp, sizeof (*sdp));
1049 }
1050
1051 static void
1052 sysdc_exitclass(void *buf)
1053 {
1054 sysdc_leave((sysdc_t *)buf);
1055 }
1056
1057 /*ARGSUSED*/
1058 static int
1059 sysdc_canexit(kthread_t *t, cred_t *reqpcredp)
1060 {
1061 /* Threads cannot exit SDC once joined, except in a body bag. */
1062 return (EPERM);
1063 }
1064
1065 static void
1066 sysdc_exit(kthread_t *t)
1067 {
1068 sysdc_t *sdc;
1069
1070 /* We're exiting, so we just rejoin the SYS class. */
1071 thread_lock(t);
1072 ASSERT(t->t_cid == sysdccid);
1073 sdc = t->t_cldata;
1074 t->t_cid = syscid;
1075 t->t_cldata = NULL;
1076 t->t_clfuncs = &(sclass[syscid].cl_funcs->thread);
1077 (void) thread_change_pri(t, maxclsyspri, 0);
1078 t->t_schedflag &= ~TS_RUNQMATCH;
1079 thread_unlock_nopreempt(t);
1080
1081 /* Unlink the sdc from everything. */
1082 sysdc_leave(sdc);
1083 }
1084
1085 /*ARGSUSED*/
1086 static int
1087 sysdc_fork(kthread_t *t, kthread_t *ct, void *bufp)
1088 {
1089 /*
1090 * Threads cannot be created with SDC as their class; they must
1091 * be created as SYS and then added with sysdc_thread_enter().
1092 * Because of this restriction, sysdc_fork() should never be called.
1093 */
1094 panic("sysdc cannot be forked");
1095
1096 return (ENOSYS);
1097 }
1098
1099 /*ARGSUSED*/
1100 static void
1101 sysdc_forkret(kthread_t *t, kthread_t *ct)
1102 {
1103 /* SDC threads are part of system processes, which never fork. */
1104 panic("sysdc cannot be forked");
1105 }
1106
1107 static pri_t
1108 sysdc_globpri(kthread_t *t)
1109 {
1110 return (t->t_epri);
1111 }
1112
1113 /*ARGSUSED*/
1114 static pri_t
1115 sysdc_no_swap(kthread_t *t, int flags)
1116 {
1117 /* SDC threads cannot be swapped. */
1118 return (-1);
1119 }
1120
1121 /*
1122 * Get maximum and minimum priorities enjoyed by SDC threads.
1123 */
1124 static int
1125 sysdc_getclpri(pcpri_t *pcprip)
1126 {
1127 pcprip->pc_clpmax = sysdc_maxpri;
1128 pcprip->pc_clpmin = sysdc_minpri;
1129 return (0);
1130 }
1131
1132 /*ARGSUSED*/
1133 static int
1134 sysdc_getclinfo(void *arg)
1135 {
1136 return (0); /* no class-specific info */
1137 }
1138
1139 /*ARGSUSED*/
1140 static int
1141 sysdc_alloc(void **p, int flag)
1142 {
1143 sysdc_t *new;
1144
1145 *p = NULL;
1146 if ((new = kmem_zalloc(sizeof (*new), flag)) == NULL) {
1147 return (ENOMEM);
1148 }
1149 if ((new->sdc_pset = kmem_zalloc(sizeof (*new->sdc_pset), flag)) ==
1150 NULL) {
1151 kmem_free(new, sizeof (*new));
1152 return (ENOMEM);
1153 }
1154 *p = new;
1155 return (0);
1156 }
1157
1158 static void
1159 sysdc_free(void *p)
1160 {
1161 sysdc_t *sdc = p;
1162
1163 if (sdc != NULL) {
1164 /*
1165 * We must have failed CL_ENTERCLASS(), so our pset should be
1166 * there and unused.
1167 */
1168 ASSERT(sdc->sdc_pset != NULL);
1169 ASSERT(sdc->sdc_pset->sdp_cpupart == NULL);
1170 kmem_free(sdc->sdc_pset, sizeof (*sdc->sdc_pset));
1171 kmem_free(sdc, sizeof (*sdc));
1172 }
1173 }
1174
1175 static int sysdc_enosys(); /* Boy, ANSI-C's K&R compatibility is weird. */
1176 static int sysdc_einval();
1177 static void sysdc_nullsys();
1178
1179 static struct classfuncs sysdc_classfuncs = {
1180 /* messages to class manager */
1181 {
1182 sysdc_enosys, /* admin */
1183 sysdc_getclinfo,
1184 sysdc_enosys, /* parmsin */
1185 sysdc_enosys, /* parmsout */
1186 sysdc_enosys, /* vaparmsin */
1187 sysdc_enosys, /* vaparmsout */
1188 sysdc_getclpri,
1189 sysdc_alloc,
1190 sysdc_free,
1191 },
1192 /* operations on threads */
1193 {
1194 sysdc_enterclass,
1195 sysdc_exitclass,
1196 sysdc_canexit,
1197 sysdc_fork,
1198 sysdc_forkret,
1199 sysdc_nullsys, /* parmsget */
1200 sysdc_enosys, /* parmsset */
1201 sysdc_nullsys, /* stop */
1202 sysdc_exit,
1203 sysdc_nullsys, /* active */
1204 sysdc_nullsys, /* inactive */
1205 sysdc_no_swap, /* swapin */
1206 sysdc_no_swap, /* swapout */
1207 sysdc_nullsys, /* trapret */
1208 sysdc_preempt,
1209 sysdc_setrun,
1210 sysdc_sleep,
1211 sysdc_tick,
1212 sysdc_wakeup,
1213 sysdc_einval, /* donice */
1214 sysdc_globpri,
1215 sysdc_nullsys, /* set_process_group */
1216 sysdc_nullsys, /* yield */
1217 sysdc_einval, /* doprio */
1218 }
1219 };
1220
1221 static int
1222 sysdc_enosys()
1223 {
1224 return (ENOSYS);
1225 }
1226
1227 static int
1228 sysdc_einval()
1229 {
1230 return (EINVAL);
1231 }
1232
1233 static void
1234 sysdc_nullsys()
1235 {
1236 }
1237
1238 /*ARGSUSED*/
1239 static pri_t
1240 sysdc_init(id_t cid, int clparmsz, classfuncs_t **clfuncspp)
1241 {
1242 int idx;
1243
1244 list_create(&sysdc_psets, sizeof (sysdc_pset_t),
1245 offsetof(sysdc_pset_t, sdp_node));
1246
1247 for (idx = 0; idx < SYSDC_NLISTS; idx++) {
1248 sysdc_active[idx].sdl_list = &sysdc_dummy;
1249 }
1250
1251 sysdc_initparam();
1252
1253 sysdccid = cid;
1254 *clfuncspp = &sysdc_classfuncs;
1255
1256 return ((pri_t)v.v_maxsyspri);
1257 }
1258
1259 static struct sclass csw = {
1260 "SDC",
1261 sysdc_init,
1262 0
1263 };
1264
1265 static struct modlsched modlsched = {
1266 &mod_schedops, "system duty cycle scheduling class", &csw
1267 };
1268
1269 static struct modlinkage modlinkage = {
1270 MODREV_1, (void *)&modlsched, NULL
1271 };
1272
1273 int
1274 _init()
1275 {
1276 return (mod_install(&modlinkage));
1277 }
1278
1279 int
1280 _fini()
1281 {
1282 return (EBUSY); /* can't unload for now */
1283 }
1284
1285 int
1286 _info(struct modinfo *modinfop)
1287 {
1288 return (mod_info(&modlinkage, modinfop));
1289 }
1290
1291 /* --- consolidation-private interfaces --- */
1292 void
1293 sysdc_thread_enter(kthread_t *t, uint_t dc, uint_t flags)
1294 {
1295 void *buf = NULL;
1296 sysdc_params_t sdp;
1297
1298 SYSDC_INC_STAT(sysdc_thread_enter_enter);
1299
1300 ASSERT(sysdc_param_init);
1301 ASSERT(sysdccid >= 0);
1302
1303 ASSERT((flags & ~SYSDC_THREAD_BATCH) == 0);
1304
1305 sdp.sdp_minpri = sysdc_minpri;
1306 sdp.sdp_maxpri = sysdc_maxpri;
1307 sdp.sdp_DC = MAX(MIN(dc, sysdc_maxDC), sysdc_minDC);
1308
1309 VERIFY0(CL_ALLOC(&buf, sysdccid, KM_SLEEP));
1310
1311 ASSERT(t->t_lwp != NULL);
1312 ASSERT(t->t_cid == syscid);
1313 ASSERT(t->t_cldata == NULL);
1314 VERIFY0(CL_CANEXIT(t, NULL));
1315 VERIFY0(CL_ENTERCLASS(t, sysdccid, &sdp, kcred, buf));
1316 CL_EXITCLASS(syscid, NULL);
1317 }