1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2001 Jake Burkholder <jake@FreeBSD.org>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29
30 #include <sys/cdefs.h>
31 __FBSDID("$FreeBSD: releng/12.0/sys/kern/kern_switch.c 335879 2018-07-03 01:55:09Z mmacy $");
32
33 #include "opt_sched.h"
34
35 #include <sys/param.h>
36 #include <sys/systm.h>
37 #include <sys/kdb.h>
38 #include <sys/kernel.h>
39 #include <sys/ktr.h>
40 #include <sys/lock.h>
41 #include <sys/mutex.h>
42 #include <sys/proc.h>
43 #include <sys/queue.h>
44 #include <sys/sched.h>
45 #include <sys/smp.h>
46 #include <sys/sysctl.h>
47
48 #include <machine/cpu.h>
49
50 /* Uncomment this to enable logging of critical_enter/exit. */
51 #if 0
52 #define KTR_CRITICAL KTR_SCHED
53 #else
54 #define KTR_CRITICAL 0
55 #endif
56
57 #ifdef FULL_PREEMPTION
58 #ifndef PREEMPTION
59 #error "The FULL_PREEMPTION option requires the PREEMPTION option"
60 #endif
61 #endif
62
63 CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS);
64
65 /*
66 * kern.sched.preemption allows user space to determine if preemption support
67 * is compiled in or not. It is not currently a boot or runtime flag that
68 * can be changed.
69 */
70 #ifdef PREEMPTION
71 static int kern_sched_preemption = 1;
72 #else
73 static int kern_sched_preemption = 0;
74 #endif
75 SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD,
76 &kern_sched_preemption, 0, "Kernel preemption enabled");
77
78 /*
79 * Support for scheduler stats exported via kern.sched.stats. All stats may
80 * be reset with kern.sched.stats.reset = 1. Stats may be defined elsewhere
81 * with SCHED_STAT_DEFINE().
82 */
83 #ifdef SCHED_STATS
84 SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats");
85
86 /* Switch reasons from mi_switch(). */
87 DPCPU_DEFINE(long, sched_switch_stats[SWT_COUNT]);
88 SCHED_STAT_DEFINE_VAR(uncategorized,
89 &DPCPU_NAME(sched_switch_stats[SWT_NONE]), "");
90 SCHED_STAT_DEFINE_VAR(preempt,
91 &DPCPU_NAME(sched_switch_stats[SWT_PREEMPT]), "");
92 SCHED_STAT_DEFINE_VAR(owepreempt,
93 &DPCPU_NAME(sched_switch_stats[SWT_OWEPREEMPT]), "");
94 SCHED_STAT_DEFINE_VAR(turnstile,
95 &DPCPU_NAME(sched_switch_stats[SWT_TURNSTILE]), "");
96 SCHED_STAT_DEFINE_VAR(sleepq,
97 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQ]), "");
98 SCHED_STAT_DEFINE_VAR(sleepqtimo,
99 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQTIMO]), "");
100 SCHED_STAT_DEFINE_VAR(relinquish,
101 &DPCPU_NAME(sched_switch_stats[SWT_RELINQUISH]), "");
102 SCHED_STAT_DEFINE_VAR(needresched,
103 &DPCPU_NAME(sched_switch_stats[SWT_NEEDRESCHED]), "");
104 SCHED_STAT_DEFINE_VAR(idle,
105 &DPCPU_NAME(sched_switch_stats[SWT_IDLE]), "");
106 SCHED_STAT_DEFINE_VAR(iwait,
107 &DPCPU_NAME(sched_switch_stats[SWT_IWAIT]), "");
108 SCHED_STAT_DEFINE_VAR(suspend,
109 &DPCPU_NAME(sched_switch_stats[SWT_SUSPEND]), "");
110 SCHED_STAT_DEFINE_VAR(remotepreempt,
111 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEPREEMPT]), "");
112 SCHED_STAT_DEFINE_VAR(remotewakeidle,
113 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEWAKEIDLE]), "");
114
115 static int
116 sysctl_stats_reset(SYSCTL_HANDLER_ARGS)
117 {
118 struct sysctl_oid *p;
119 uintptr_t counter;
120 int error;
121 int val;
122 int i;
123
124 val = 0;
125 error = sysctl_handle_int(oidp, &val, 0, req);
126 if (error != 0 || req->newptr == NULL)
127 return (error);
128 if (val == 0)
129 return (0);
130 /*
131 * Traverse the list of children of _kern_sched_stats and reset each
132 * to 0. Skip the reset entry.
133 */
134 SLIST_FOREACH(p, oidp->oid_parent, oid_link) {
135 if (p == oidp || p->oid_arg1 == NULL)
136 continue;
137 counter = (uintptr_t)p->oid_arg1;
138 CPU_FOREACH(i) {
139 *(long *)(dpcpu_off[i] + counter) = 0;
140 }
141 }
142 return (0);
143 }
144
145 SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL,
146 0, sysctl_stats_reset, "I", "Reset scheduler statistics");
147 #endif
148
149 /************************************************************************
150 * Functions that manipulate runnability from a thread perspective. *
151 ************************************************************************/
152 /*
153 * Select the thread that will be run next.
154 */
155
156 static __noinline struct thread *
157 choosethread_panic(struct thread *td)
158 {
159
160 /*
161 * If we are in panic, only allow system threads,
162 * plus the one we are running in, to be run.
163 */
164 retry:
165 if (((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 td = sched_choose();
170 goto retry;
171 }
172
173 TD_SET_RUNNING(td);
174 return (td);
175 }
176
177 struct thread *
178 choosethread(void)
179 {
180 struct thread *td;
181
182 td = sched_choose();
183
184 if (__predict_false(panicstr != NULL))
185 return (choosethread_panic(td));
186
187 TD_SET_RUNNING(td);
188 return (td);
189 }
190
191 /*
192 * Kernel thread preemption implementation. Critical sections mark
193 * regions of code in which preemptions are not allowed.
194 *
195 * It might seem a good idea to inline critical_enter() but, in order
196 * to prevent instructions reordering by the compiler, a __compiler_membar()
197 * would have to be used here (the same as sched_pin()). The performance
198 * penalty imposed by the membar could, then, produce slower code than
199 * the function call itself, for most cases.
200 */
201 void
202 critical_enter_KBI(void)
203 {
204 #ifdef KTR
205 struct thread *td = curthread;
206 #endif
207 critical_enter();
208 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td,
209 (long)td->td_proc->p_pid, td->td_name, td->td_critnest);
210 }
211
212 void __noinline
213 critical_exit_preempt(void)
214 {
215 struct thread *td;
216 int flags;
217
218 /*
219 * If td_critnest is 0, it is possible that we are going to get
220 * preempted again before reaching the code below. This happens
221 * rarely and is harmless. However, this means td_owepreempt may
222 * now be unset.
223 */
224 td = curthread;
225 if (td->td_critnest != 0)
226 return;
227 if (kdb_active)
228 return;
229
230 /*
231 * Microoptimization: we committed to switch,
232 * disable preemption in interrupt handlers
233 * while spinning for the thread lock.
234 */
235 td->td_critnest = 1;
236 thread_lock(td);
237 td->td_critnest--;
238 flags = SW_INVOL | SW_PREEMPT;
239 if (TD_IS_IDLETHREAD(td))
240 flags |= SWT_IDLE;
241 else
242 flags |= SWT_OWEPREEMPT;
243 mi_switch(flags, NULL);
244 thread_unlock(td);
245 }
246
247 void
248 critical_exit_KBI(void)
249 {
250 #ifdef KTR
251 struct thread *td = curthread;
252 #endif
253 critical_exit();
254 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td,
255 (long)td->td_proc->p_pid, td->td_name, td->td_critnest);
256 }
257
258 /************************************************************************
259 * SYSTEM RUN QUEUE manipulations and tests *
260 ************************************************************************/
261 /*
262 * Initialize a run structure.
263 */
264 void
265 runq_init(struct runq *rq)
266 {
267 int i;
268
269 bzero(rq, sizeof *rq);
270 for (i = 0; i < RQ_NQS; i++)
271 TAILQ_INIT(&rq->rq_queues[i]);
272 }
273
274 /*
275 * Clear the status bit of the queue corresponding to priority level pri,
276 * indicating that it is empty.
277 */
278 static __inline void
279 runq_clrbit(struct runq *rq, int pri)
280 {
281 struct rqbits *rqb;
282
283 rqb = &rq->rq_status;
284 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d",
285 rqb->rqb_bits[RQB_WORD(pri)],
286 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri),
287 RQB_BIT(pri), RQB_WORD(pri));
288 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri);
289 }
290
291 /*
292 * Find the index of the first non-empty run queue. This is done by
293 * scanning the status bits, a set bit indicates a non-empty queue.
294 */
295 static __inline int
296 runq_findbit(struct runq *rq)
297 {
298 struct rqbits *rqb;
299 int pri;
300 int i;
301
302 rqb = &rq->rq_status;
303 for (i = 0; i < RQB_LEN; i++)
304 if (rqb->rqb_bits[i]) {
305 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW);
306 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d",
307 rqb->rqb_bits[i], i, pri);
308 return (pri);
309 }
310
311 return (-1);
312 }
313
314 static __inline int
315 runq_findbit_from(struct runq *rq, u_char pri)
316 {
317 struct rqbits *rqb;
318 rqb_word_t mask;
319 int i;
320
321 /*
322 * Set the mask for the first word so we ignore priorities before 'pri'.
323 */
324 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1));
325 rqb = &rq->rq_status;
326 again:
327 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) {
328 mask = rqb->rqb_bits[i] & mask;
329 if (mask == 0)
330 continue;
331 pri = RQB_FFS(mask) + (i << RQB_L2BPW);
332 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d",
333 mask, i, pri);
334 return (pri);
335 }
336 if (pri == 0)
337 return (-1);
338 /*
339 * Wrap back around to the beginning of the list just once so we
340 * scan the whole thing.
341 */
342 pri = 0;
343 goto again;
344 }
345
346 /*
347 * Set the status bit of the queue corresponding to priority level pri,
348 * indicating that it is non-empty.
349 */
350 static __inline void
351 runq_setbit(struct runq *rq, int pri)
352 {
353 struct rqbits *rqb;
354
355 rqb = &rq->rq_status;
356 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d",
357 rqb->rqb_bits[RQB_WORD(pri)],
358 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri),
359 RQB_BIT(pri), RQB_WORD(pri));
360 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri);
361 }
362
363 /*
364 * Add the thread to the queue specified by its priority, and set the
365 * corresponding status bit.
366 */
367 void
368 runq_add(struct runq *rq, struct thread *td, int flags)
369 {
370 struct rqhead *rqh;
371 int pri;
372
373 pri = td->td_priority / RQ_PPQ;
374 td->td_rqindex = pri;
375 runq_setbit(rq, pri);
376 rqh = &rq->rq_queues[pri];
377 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p",
378 td, td->td_priority, pri, rqh);
379 if (flags & SRQ_PREEMPTED) {
380 TAILQ_INSERT_HEAD(rqh, td, td_runq);
381 } else {
382 TAILQ_INSERT_TAIL(rqh, td, td_runq);
383 }
384 }
385
386 void
387 runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags)
388 {
389 struct rqhead *rqh;
390
391 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri));
392 td->td_rqindex = pri;
393 runq_setbit(rq, pri);
394 rqh = &rq->rq_queues[pri];
395 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p",
396 td, td->td_priority, pri, rqh);
397 if (flags & SRQ_PREEMPTED) {
398 TAILQ_INSERT_HEAD(rqh, td, td_runq);
399 } else {
400 TAILQ_INSERT_TAIL(rqh, td, td_runq);
401 }
402 }
403 /*
404 * Return true if there are runnable processes of any priority on the run
405 * queue, false otherwise. Has no side effects, does not modify the run
406 * queue structure.
407 */
408 int
409 runq_check(struct runq *rq)
410 {
411 struct rqbits *rqb;
412 int i;
413
414 rqb = &rq->rq_status;
415 for (i = 0; i < RQB_LEN; i++)
416 if (rqb->rqb_bits[i]) {
417 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d",
418 rqb->rqb_bits[i], i);
419 return (1);
420 }
421 CTR0(KTR_RUNQ, "runq_check: empty");
422
423 return (0);
424 }
425
426 /*
427 * Find the highest priority process on the run queue.
428 */
429 struct thread *
430 runq_choose_fuzz(struct runq *rq, int fuzz)
431 {
432 struct rqhead *rqh;
433 struct thread *td;
434 int pri;
435
436 while ((pri = runq_findbit(rq)) != -1) {
437 rqh = &rq->rq_queues[pri];
438 /* fuzz == 1 is normal.. 0 or less are ignored */
439 if (fuzz > 1) {
440 /*
441 * In the first couple of entries, check if
442 * there is one for our CPU as a preference.
443 */
444 int count = fuzz;
445 int cpu = PCPU_GET(cpuid);
446 struct thread *td2;
447 td2 = td = TAILQ_FIRST(rqh);
448
449 while (count-- && td2) {
450 if (td2->td_lastcpu == cpu) {
451 td = td2;
452 break;
453 }
454 td2 = TAILQ_NEXT(td2, td_runq);
455 }
456 } else
457 td = TAILQ_FIRST(rqh);
458 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue"));
459 CTR3(KTR_RUNQ,
460 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh);
461 return (td);
462 }
463 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri);
464
465 return (NULL);
466 }
467
468 /*
469 * Find the highest priority process on the run queue.
470 */
471 struct thread *
472 runq_choose(struct runq *rq)
473 {
474 struct rqhead *rqh;
475 struct thread *td;
476 int pri;
477
478 while ((pri = runq_findbit(rq)) != -1) {
479 rqh = &rq->rq_queues[pri];
480 td = TAILQ_FIRST(rqh);
481 KASSERT(td != NULL, ("runq_choose: no thread on busy queue"));
482 CTR3(KTR_RUNQ,
483 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh);
484 return (td);
485 }
486 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri);
487
488 return (NULL);
489 }
490
491 struct thread *
492 runq_choose_from(struct runq *rq, u_char idx)
493 {
494 struct rqhead *rqh;
495 struct thread *td;
496 int pri;
497
498 if ((pri = runq_findbit_from(rq, idx)) != -1) {
499 rqh = &rq->rq_queues[pri];
500 td = TAILQ_FIRST(rqh);
501 KASSERT(td != NULL, ("runq_choose: no thread on busy queue"));
502 CTR4(KTR_RUNQ,
503 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p",
504 pri, td, td->td_rqindex, rqh);
505 return (td);
506 }
507 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri);
508
509 return (NULL);
510 }
511 /*
512 * Remove the thread from the queue specified by its priority, and clear the
513 * corresponding status bit if the queue becomes empty.
514 * Caller must set state afterwards.
515 */
516 void
517 runq_remove(struct runq *rq, struct thread *td)
518 {
519
520 runq_remove_idx(rq, td, NULL);
521 }
522
523 void
524 runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx)
525 {
526 struct rqhead *rqh;
527 u_char pri;
528
529 KASSERT(td->td_flags & TDF_INMEM,
530 ("runq_remove_idx: thread swapped out"));
531 pri = td->td_rqindex;
532 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri));
533 rqh = &rq->rq_queues[pri];
534 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p",
535 td, td->td_priority, pri, rqh);
536 TAILQ_REMOVE(rqh, td, td_runq);
537 if (TAILQ_EMPTY(rqh)) {
538 CTR0(KTR_RUNQ, "runq_remove_idx: empty");
539 runq_clrbit(rq, pri);
540 if (idx != NULL && *idx == pri)
541 *idx = (pri + 1) % RQ_NQS;
542 }
543 }
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