1 /*-
2 * Copyright (c) 2001 Jake Burkholder <jake@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27
28 #include <sys/cdefs.h>
29 __FBSDID("$FreeBSD$");
30
31 #include "opt_sched.h"
32
33 #include <sys/param.h>
34 #include <sys/systm.h>
35 #include <sys/kdb.h>
36 #include <sys/kernel.h>
37 #include <sys/ktr.h>
38 #include <sys/lock.h>
39 #include <sys/mutex.h>
40 #include <sys/proc.h>
41 #include <sys/queue.h>
42 #include <sys/sched.h>
43 #include <sys/smp.h>
44 #include <sys/sysctl.h>
45
46 #include <machine/cpu.h>
47
48 /* Uncomment this to enable logging of critical_enter/exit. */
49 #if 0
50 #define KTR_CRITICAL KTR_SCHED
51 #else
52 #define KTR_CRITICAL 0
53 #endif
54
55 #ifdef FULL_PREEMPTION
56 #ifndef PREEMPTION
57 #error "The FULL_PREEMPTION option requires the PREEMPTION option"
58 #endif
59 #endif
60
61 CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS);
62
63 /*
64 * kern.sched.preemption allows user space to determine if preemption support
65 * is compiled in or not. It is not currently a boot or runtime flag that
66 * can be changed.
67 */
68 #ifdef PREEMPTION
69 static int kern_sched_preemption = 1;
70 #else
71 static int kern_sched_preemption = 0;
72 #endif
73 SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD,
74 &kern_sched_preemption, 0, "Kernel preemption enabled");
75
76 /*
77 * Support for scheduler stats exported via kern.sched.stats. All stats may
78 * be reset with kern.sched.stats.reset = 1. Stats may be defined elsewhere
79 * with SCHED_STAT_DEFINE().
80 */
81 #ifdef SCHED_STATS
82 SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats");
83
84 /* Switch reasons from mi_switch(). */
85 DPCPU_DEFINE(long, sched_switch_stats[SWT_COUNT]);
86 SCHED_STAT_DEFINE_VAR(uncategorized,
87 &DPCPU_NAME(sched_switch_stats[SWT_NONE]), "");
88 SCHED_STAT_DEFINE_VAR(preempt,
89 &DPCPU_NAME(sched_switch_stats[SWT_PREEMPT]), "");
90 SCHED_STAT_DEFINE_VAR(owepreempt,
91 &DPCPU_NAME(sched_switch_stats[SWT_OWEPREEMPT]), "");
92 SCHED_STAT_DEFINE_VAR(turnstile,
93 &DPCPU_NAME(sched_switch_stats[SWT_TURNSTILE]), "");
94 SCHED_STAT_DEFINE_VAR(sleepq,
95 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQ]), "");
96 SCHED_STAT_DEFINE_VAR(sleepqtimo,
97 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQTIMO]), "");
98 SCHED_STAT_DEFINE_VAR(relinquish,
99 &DPCPU_NAME(sched_switch_stats[SWT_RELINQUISH]), "");
100 SCHED_STAT_DEFINE_VAR(needresched,
101 &DPCPU_NAME(sched_switch_stats[SWT_NEEDRESCHED]), "");
102 SCHED_STAT_DEFINE_VAR(idle,
103 &DPCPU_NAME(sched_switch_stats[SWT_IDLE]), "");
104 SCHED_STAT_DEFINE_VAR(iwait,
105 &DPCPU_NAME(sched_switch_stats[SWT_IWAIT]), "");
106 SCHED_STAT_DEFINE_VAR(suspend,
107 &DPCPU_NAME(sched_switch_stats[SWT_SUSPEND]), "");
108 SCHED_STAT_DEFINE_VAR(remotepreempt,
109 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEPREEMPT]), "");
110 SCHED_STAT_DEFINE_VAR(remotewakeidle,
111 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEWAKEIDLE]), "");
112
113 static int
114 sysctl_stats_reset(SYSCTL_HANDLER_ARGS)
115 {
116 struct sysctl_oid *p;
117 uintptr_t counter;
118 int error;
119 int val;
120 int i;
121
122 val = 0;
123 error = sysctl_handle_int(oidp, &val, 0, req);
124 if (error != 0 || req->newptr == NULL)
125 return (error);
126 if (val == 0)
127 return (0);
128 /*
129 * Traverse the list of children of _kern_sched_stats and reset each
130 * to 0. Skip the reset entry.
131 */
132 SLIST_FOREACH(p, oidp->oid_parent, oid_link) {
133 if (p == oidp || p->oid_arg1 == NULL)
134 continue;
135 counter = (uintptr_t)p->oid_arg1;
136 CPU_FOREACH(i) {
137 *(long *)(dpcpu_off[i] + counter) = 0;
138 }
139 }
140 return (0);
141 }
142
143 SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL,
144 0, sysctl_stats_reset, "I", "Reset scheduler statistics");
145 #endif
146
147 /************************************************************************
148 * Functions that manipulate runnability from a thread perspective. *
149 ************************************************************************/
150 /*
151 * Select the thread that will be run next.
152 */
153 struct thread *
154 choosethread(void)
155 {
156 struct thread *td;
157
158 retry:
159 td = sched_choose();
160
161 /*
162 * If we are in panic, only allow system threads,
163 * plus the one we are running in, to be run.
164 */
165 if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 &&
166 (td->td_flags & TDF_INPANIC) == 0)) {
167 /* note that it is no longer on the run queue */
168 TD_SET_CAN_RUN(td);
169 goto retry;
170 }
171
172 TD_SET_RUNNING(td);
173 return (td);
174 }
175
176 /*
177 * Kernel thread preemption implementation. Critical sections mark
178 * regions of code in which preemptions are not allowed.
179 *
180 * It might seem a good idea to inline critical_enter() but, in order
181 * to prevent instructions reordering by the compiler, a __compiler_membar()
182 * would have to be used here (the same as sched_pin()). The performance
183 * penalty imposed by the membar could, then, produce slower code than
184 * the function call itself, for most cases.
185 */
186 void
187 critical_enter(void)
188 {
189 struct thread *td;
190
191 td = curthread;
192 td->td_critnest++;
193 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td,
194 (long)td->td_proc->p_pid, td->td_name, td->td_critnest);
195 }
196
197 void
198 critical_exit(void)
199 {
200 struct thread *td;
201 int flags;
202
203 td = curthread;
204 KASSERT(td->td_critnest != 0,
205 ("critical_exit: td_critnest == 0"));
206
207 if (td->td_critnest == 1) {
208 td->td_critnest = 0;
209
210 /*
211 * Interrupt handlers execute critical_exit() on
212 * leave, and td_owepreempt may be left set by an
213 * interrupt handler only when td_critnest > 0. If we
214 * are decrementing td_critnest from 1 to 0, read
215 * td_owepreempt after decrementing, to not miss the
216 * preempt. Disallow compiler to reorder operations.
217 */
218 __compiler_membar();
219 if (td->td_owepreempt && !kdb_active) {
220 /*
221 * Microoptimization: we committed to switch,
222 * disable preemption in interrupt handlers
223 * while spinning for the thread lock.
224 */
225 td->td_critnest = 1;
226 thread_lock(td);
227 td->td_critnest--;
228 flags = SW_INVOL | SW_PREEMPT;
229 if (TD_IS_IDLETHREAD(td))
230 flags |= SWT_IDLE;
231 else
232 flags |= SWT_OWEPREEMPT;
233 mi_switch(flags, NULL);
234 thread_unlock(td);
235 }
236 } else
237 td->td_critnest--;
238
239 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td,
240 (long)td->td_proc->p_pid, td->td_name, td->td_critnest);
241 }
242
243 /************************************************************************
244 * SYSTEM RUN QUEUE manipulations and tests *
245 ************************************************************************/
246 /*
247 * Initialize a run structure.
248 */
249 void
250 runq_init(struct runq *rq)
251 {
252 int i;
253
254 bzero(rq, sizeof *rq);
255 for (i = 0; i < RQ_NQS; i++)
256 TAILQ_INIT(&rq->rq_queues[i]);
257 }
258
259 /*
260 * Clear the status bit of the queue corresponding to priority level pri,
261 * indicating that it is empty.
262 */
263 static __inline void
264 runq_clrbit(struct runq *rq, int pri)
265 {
266 struct rqbits *rqb;
267
268 rqb = &rq->rq_status;
269 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d",
270 rqb->rqb_bits[RQB_WORD(pri)],
271 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri),
272 RQB_BIT(pri), RQB_WORD(pri));
273 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri);
274 }
275
276 /*
277 * Find the index of the first non-empty run queue. This is done by
278 * scanning the status bits, a set bit indicates a non-empty queue.
279 */
280 static __inline int
281 runq_findbit(struct runq *rq)
282 {
283 struct rqbits *rqb;
284 int pri;
285 int i;
286
287 rqb = &rq->rq_status;
288 for (i = 0; i < RQB_LEN; i++)
289 if (rqb->rqb_bits[i]) {
290 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW);
291 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d",
292 rqb->rqb_bits[i], i, pri);
293 return (pri);
294 }
295
296 return (-1);
297 }
298
299 static __inline int
300 runq_findbit_from(struct runq *rq, u_char pri)
301 {
302 struct rqbits *rqb;
303 rqb_word_t mask;
304 int i;
305
306 /*
307 * Set the mask for the first word so we ignore priorities before 'pri'.
308 */
309 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1));
310 rqb = &rq->rq_status;
311 again:
312 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) {
313 mask = rqb->rqb_bits[i] & mask;
314 if (mask == 0)
315 continue;
316 pri = RQB_FFS(mask) + (i << RQB_L2BPW);
317 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d",
318 mask, i, pri);
319 return (pri);
320 }
321 if (pri == 0)
322 return (-1);
323 /*
324 * Wrap back around to the beginning of the list just once so we
325 * scan the whole thing.
326 */
327 pri = 0;
328 goto again;
329 }
330
331 /*
332 * Set the status bit of the queue corresponding to priority level pri,
333 * indicating that it is non-empty.
334 */
335 static __inline void
336 runq_setbit(struct runq *rq, int pri)
337 {
338 struct rqbits *rqb;
339
340 rqb = &rq->rq_status;
341 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d",
342 rqb->rqb_bits[RQB_WORD(pri)],
343 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri),
344 RQB_BIT(pri), RQB_WORD(pri));
345 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri);
346 }
347
348 /*
349 * Add the thread to the queue specified by its priority, and set the
350 * corresponding status bit.
351 */
352 void
353 runq_add(struct runq *rq, struct thread *td, int flags)
354 {
355 struct rqhead *rqh;
356 int pri;
357
358 pri = td->td_priority / RQ_PPQ;
359 td->td_rqindex = pri;
360 runq_setbit(rq, pri);
361 rqh = &rq->rq_queues[pri];
362 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p",
363 td, td->td_priority, pri, rqh);
364 if (flags & SRQ_PREEMPTED) {
365 TAILQ_INSERT_HEAD(rqh, td, td_runq);
366 } else {
367 TAILQ_INSERT_TAIL(rqh, td, td_runq);
368 }
369 }
370
371 void
372 runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags)
373 {
374 struct rqhead *rqh;
375
376 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri));
377 td->td_rqindex = pri;
378 runq_setbit(rq, pri);
379 rqh = &rq->rq_queues[pri];
380 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p",
381 td, td->td_priority, pri, rqh);
382 if (flags & SRQ_PREEMPTED) {
383 TAILQ_INSERT_HEAD(rqh, td, td_runq);
384 } else {
385 TAILQ_INSERT_TAIL(rqh, td, td_runq);
386 }
387 }
388 /*
389 * Return true if there are runnable processes of any priority on the run
390 * queue, false otherwise. Has no side effects, does not modify the run
391 * queue structure.
392 */
393 int
394 runq_check(struct runq *rq)
395 {
396 struct rqbits *rqb;
397 int i;
398
399 rqb = &rq->rq_status;
400 for (i = 0; i < RQB_LEN; i++)
401 if (rqb->rqb_bits[i]) {
402 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d",
403 rqb->rqb_bits[i], i);
404 return (1);
405 }
406 CTR0(KTR_RUNQ, "runq_check: empty");
407
408 return (0);
409 }
410
411 /*
412 * Find the highest priority process on the run queue.
413 */
414 struct thread *
415 runq_choose_fuzz(struct runq *rq, int fuzz)
416 {
417 struct rqhead *rqh;
418 struct thread *td;
419 int pri;
420
421 while ((pri = runq_findbit(rq)) != -1) {
422 rqh = &rq->rq_queues[pri];
423 /* fuzz == 1 is normal.. 0 or less are ignored */
424 if (fuzz > 1) {
425 /*
426 * In the first couple of entries, check if
427 * there is one for our CPU as a preference.
428 */
429 int count = fuzz;
430 int cpu = PCPU_GET(cpuid);
431 struct thread *td2;
432 td2 = td = TAILQ_FIRST(rqh);
433
434 while (count-- && td2) {
435 if (td2->td_lastcpu == cpu) {
436 td = td2;
437 break;
438 }
439 td2 = TAILQ_NEXT(td2, td_runq);
440 }
441 } else
442 td = TAILQ_FIRST(rqh);
443 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue"));
444 CTR3(KTR_RUNQ,
445 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh);
446 return (td);
447 }
448 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri);
449
450 return (NULL);
451 }
452
453 /*
454 * Find the highest priority process on the run queue.
455 */
456 struct thread *
457 runq_choose(struct runq *rq)
458 {
459 struct rqhead *rqh;
460 struct thread *td;
461 int pri;
462
463 while ((pri = runq_findbit(rq)) != -1) {
464 rqh = &rq->rq_queues[pri];
465 td = TAILQ_FIRST(rqh);
466 KASSERT(td != NULL, ("runq_choose: no thread on busy queue"));
467 CTR3(KTR_RUNQ,
468 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh);
469 return (td);
470 }
471 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri);
472
473 return (NULL);
474 }
475
476 struct thread *
477 runq_choose_from(struct runq *rq, u_char idx)
478 {
479 struct rqhead *rqh;
480 struct thread *td;
481 int pri;
482
483 if ((pri = runq_findbit_from(rq, idx)) != -1) {
484 rqh = &rq->rq_queues[pri];
485 td = TAILQ_FIRST(rqh);
486 KASSERT(td != NULL, ("runq_choose: no thread on busy queue"));
487 CTR4(KTR_RUNQ,
488 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p",
489 pri, td, td->td_rqindex, rqh);
490 return (td);
491 }
492 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri);
493
494 return (NULL);
495 }
496 /*
497 * Remove the thread from the queue specified by its priority, and clear the
498 * corresponding status bit if the queue becomes empty.
499 * Caller must set state afterwards.
500 */
501 void
502 runq_remove(struct runq *rq, struct thread *td)
503 {
504
505 runq_remove_idx(rq, td, NULL);
506 }
507
508 void
509 runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx)
510 {
511 struct rqhead *rqh;
512 u_char pri;
513
514 KASSERT(td->td_flags & TDF_INMEM,
515 ("runq_remove_idx: thread swapped out"));
516 pri = td->td_rqindex;
517 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri));
518 rqh = &rq->rq_queues[pri];
519 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p",
520 td, td->td_priority, pri, rqh);
521 TAILQ_REMOVE(rqh, td, td_runq);
522 if (TAILQ_EMPTY(rqh)) {
523 CTR0(KTR_RUNQ, "runq_remove_idx: empty");
524 runq_clrbit(rq, pri);
525 if (idx != NULL && *idx == pri)
526 *idx = (pri + 1) % RQ_NQS;
527 }
528 }
Cache object: e2ad6538cc5a769ea28ea291db8c4580
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