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
154 static __noinline struct thread *
155 choosethread_panic(struct thread *td)
156 {
157
158 /*
159 * If we are in panic, only allow system threads,
160 * plus the one we are running in, to be run.
161 */
162 retry:
163 if (((td->td_proc->p_flag & P_SYSTEM) == 0 &&
164 (td->td_flags & TDF_INPANIC) == 0)) {
165 /* note that it is no longer on the run queue */
166 TD_SET_CAN_RUN(td);
167 td = sched_choose();
168 goto retry;
169 }
170
171 TD_SET_RUNNING(td);
172 return (td);
173 }
174
175 struct thread *
176 choosethread(void)
177 {
178 struct thread *td;
179
180 td = sched_choose();
181
182 if (__predict_false(panicstr != NULL))
183 return (choosethread_panic(td));
184
185 TD_SET_RUNNING(td);
186 return (td);
187 }
188
189 /*
190 * Kernel thread preemption implementation. Critical sections mark
191 * regions of code in which preemptions are not allowed.
192 *
193 * It might seem a good idea to inline critical_enter() but, in order
194 * to prevent instructions reordering by the compiler, a __compiler_membar()
195 * would have to be used here (the same as sched_pin()). The performance
196 * penalty imposed by the membar could, then, produce slower code than
197 * the function call itself, for most cases.
198 */
199 void
200 critical_enter(void)
201 {
202 struct thread *td;
203
204 td = curthread;
205 td->td_critnest++;
206 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td,
207 (long)td->td_proc->p_pid, td->td_name, td->td_critnest);
208 }
209
210 void
211 critical_exit(void)
212 {
213 struct thread *td;
214 int flags;
215
216 td = curthread;
217 KASSERT(td->td_critnest != 0,
218 ("critical_exit: td_critnest == 0"));
219
220 if (td->td_critnest == 1) {
221 td->td_critnest = 0;
222
223 /*
224 * Interrupt handlers execute critical_exit() on
225 * leave, and td_owepreempt may be left set by an
226 * interrupt handler only when td_critnest > 0. If we
227 * are decrementing td_critnest from 1 to 0, read
228 * td_owepreempt after decrementing, to not miss the
229 * preempt. Disallow compiler to reorder operations.
230 */
231 __compiler_membar();
232 if (td->td_owepreempt && !kdb_active) {
233 /*
234 * Microoptimization: we committed to switch,
235 * disable preemption in interrupt handlers
236 * while spinning for the thread lock.
237 */
238 td->td_critnest = 1;
239 thread_lock(td);
240 td->td_critnest--;
241 flags = SW_INVOL | SW_PREEMPT;
242 if (TD_IS_IDLETHREAD(td))
243 flags |= SWT_IDLE;
244 else
245 flags |= SWT_OWEPREEMPT;
246 mi_switch(flags, NULL);
247 thread_unlock(td);
248 }
249 } else
250 td->td_critnest--;
251
252 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td,
253 (long)td->td_proc->p_pid, td->td_name, td->td_critnest);
254 }
255
256 /************************************************************************
257 * SYSTEM RUN QUEUE manipulations and tests *
258 ************************************************************************/
259 /*
260 * Initialize a run structure.
261 */
262 void
263 runq_init(struct runq *rq)
264 {
265 int i;
266
267 bzero(rq, sizeof *rq);
268 for (i = 0; i < RQ_NQS; i++)
269 TAILQ_INIT(&rq->rq_queues[i]);
270 }
271
272 /*
273 * Clear the status bit of the queue corresponding to priority level pri,
274 * indicating that it is empty.
275 */
276 static __inline void
277 runq_clrbit(struct runq *rq, int pri)
278 {
279 struct rqbits *rqb;
280
281 rqb = &rq->rq_status;
282 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d",
283 rqb->rqb_bits[RQB_WORD(pri)],
284 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri),
285 RQB_BIT(pri), RQB_WORD(pri));
286 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri);
287 }
288
289 /*
290 * Find the index of the first non-empty run queue. This is done by
291 * scanning the status bits, a set bit indicates a non-empty queue.
292 */
293 static __inline int
294 runq_findbit(struct runq *rq)
295 {
296 struct rqbits *rqb;
297 int pri;
298 int i;
299
300 rqb = &rq->rq_status;
301 for (i = 0; i < RQB_LEN; i++)
302 if (rqb->rqb_bits[i]) {
303 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW);
304 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d",
305 rqb->rqb_bits[i], i, pri);
306 return (pri);
307 }
308
309 return (-1);
310 }
311
312 static __inline int
313 runq_findbit_from(struct runq *rq, u_char pri)
314 {
315 struct rqbits *rqb;
316 rqb_word_t mask;
317 int i;
318
319 /*
320 * Set the mask for the first word so we ignore priorities before 'pri'.
321 */
322 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1));
323 rqb = &rq->rq_status;
324 again:
325 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) {
326 mask = rqb->rqb_bits[i] & mask;
327 if (mask == 0)
328 continue;
329 pri = RQB_FFS(mask) + (i << RQB_L2BPW);
330 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d",
331 mask, i, pri);
332 return (pri);
333 }
334 if (pri == 0)
335 return (-1);
336 /*
337 * Wrap back around to the beginning of the list just once so we
338 * scan the whole thing.
339 */
340 pri = 0;
341 goto again;
342 }
343
344 /*
345 * Set the status bit of the queue corresponding to priority level pri,
346 * indicating that it is non-empty.
347 */
348 static __inline void
349 runq_setbit(struct runq *rq, int pri)
350 {
351 struct rqbits *rqb;
352
353 rqb = &rq->rq_status;
354 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d",
355 rqb->rqb_bits[RQB_WORD(pri)],
356 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri),
357 RQB_BIT(pri), RQB_WORD(pri));
358 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri);
359 }
360
361 /*
362 * Add the thread to the queue specified by its priority, and set the
363 * corresponding status bit.
364 */
365 void
366 runq_add(struct runq *rq, struct thread *td, int flags)
367 {
368 struct rqhead *rqh;
369 int pri;
370
371 pri = td->td_priority / RQ_PPQ;
372 td->td_rqindex = pri;
373 runq_setbit(rq, pri);
374 rqh = &rq->rq_queues[pri];
375 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p",
376 td, td->td_priority, pri, rqh);
377 if (flags & SRQ_PREEMPTED) {
378 TAILQ_INSERT_HEAD(rqh, td, td_runq);
379 } else {
380 TAILQ_INSERT_TAIL(rqh, td, td_runq);
381 }
382 }
383
384 void
385 runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags)
386 {
387 struct rqhead *rqh;
388
389 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri));
390 td->td_rqindex = pri;
391 runq_setbit(rq, pri);
392 rqh = &rq->rq_queues[pri];
393 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p",
394 td, td->td_priority, pri, rqh);
395 if (flags & SRQ_PREEMPTED) {
396 TAILQ_INSERT_HEAD(rqh, td, td_runq);
397 } else {
398 TAILQ_INSERT_TAIL(rqh, td, td_runq);
399 }
400 }
401 /*
402 * Return true if there are runnable processes of any priority on the run
403 * queue, false otherwise. Has no side effects, does not modify the run
404 * queue structure.
405 */
406 int
407 runq_check(struct runq *rq)
408 {
409 struct rqbits *rqb;
410 int i;
411
412 rqb = &rq->rq_status;
413 for (i = 0; i < RQB_LEN; i++)
414 if (rqb->rqb_bits[i]) {
415 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d",
416 rqb->rqb_bits[i], i);
417 return (1);
418 }
419 CTR0(KTR_RUNQ, "runq_check: empty");
420
421 return (0);
422 }
423
424 /*
425 * Find the highest priority process on the run queue.
426 */
427 struct thread *
428 runq_choose_fuzz(struct runq *rq, int fuzz)
429 {
430 struct rqhead *rqh;
431 struct thread *td;
432 int pri;
433
434 while ((pri = runq_findbit(rq)) != -1) {
435 rqh = &rq->rq_queues[pri];
436 /* fuzz == 1 is normal.. 0 or less are ignored */
437 if (fuzz > 1) {
438 /*
439 * In the first couple of entries, check if
440 * there is one for our CPU as a preference.
441 */
442 int count = fuzz;
443 int cpu = PCPU_GET(cpuid);
444 struct thread *td2;
445 td2 = td = TAILQ_FIRST(rqh);
446
447 while (count-- && td2) {
448 if (td2->td_lastcpu == cpu) {
449 td = td2;
450 break;
451 }
452 td2 = TAILQ_NEXT(td2, td_runq);
453 }
454 } else
455 td = TAILQ_FIRST(rqh);
456 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue"));
457 CTR3(KTR_RUNQ,
458 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh);
459 return (td);
460 }
461 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri);
462
463 return (NULL);
464 }
465
466 /*
467 * Find the highest priority process on the run queue.
468 */
469 struct thread *
470 runq_choose(struct runq *rq)
471 {
472 struct rqhead *rqh;
473 struct thread *td;
474 int pri;
475
476 while ((pri = runq_findbit(rq)) != -1) {
477 rqh = &rq->rq_queues[pri];
478 td = TAILQ_FIRST(rqh);
479 KASSERT(td != NULL, ("runq_choose: no thread on busy queue"));
480 CTR3(KTR_RUNQ,
481 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh);
482 return (td);
483 }
484 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri);
485
486 return (NULL);
487 }
488
489 struct thread *
490 runq_choose_from(struct runq *rq, u_char idx)
491 {
492 struct rqhead *rqh;
493 struct thread *td;
494 int pri;
495
496 if ((pri = runq_findbit_from(rq, idx)) != -1) {
497 rqh = &rq->rq_queues[pri];
498 td = TAILQ_FIRST(rqh);
499 KASSERT(td != NULL, ("runq_choose: no thread on busy queue"));
500 CTR4(KTR_RUNQ,
501 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p",
502 pri, td, td->td_rqindex, rqh);
503 return (td);
504 }
505 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri);
506
507 return (NULL);
508 }
509 /*
510 * Remove the thread from the queue specified by its priority, and clear the
511 * corresponding status bit if the queue becomes empty.
512 * Caller must set state afterwards.
513 */
514 void
515 runq_remove(struct runq *rq, struct thread *td)
516 {
517
518 runq_remove_idx(rq, td, NULL);
519 }
520
521 void
522 runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx)
523 {
524 struct rqhead *rqh;
525 u_char pri;
526
527 KASSERT(td->td_flags & TDF_INMEM,
528 ("runq_remove_idx: thread swapped out"));
529 pri = td->td_rqindex;
530 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri));
531 rqh = &rq->rq_queues[pri];
532 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p",
533 td, td->td_priority, pri, rqh);
534 TAILQ_REMOVE(rqh, td, td_runq);
535 if (TAILQ_EMPTY(rqh)) {
536 CTR0(KTR_RUNQ, "runq_remove_idx: empty");
537 runq_clrbit(rq, pri);
538 if (idx != NULL && *idx == pri)
539 *idx = (pri + 1) % RQ_NQS;
540 }
541 }
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