source: mainline/kernel/generic/src/proc/scheduler.c@ 473e693

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 473e693 was 48d14222, checked in by Jakub Jermar <jakub@…>, 18 years ago

JoinMe → Lingering
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File size: 16.4 KB
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1/*
2 * Copyright (c) 2001-2007 Jakub Jermar
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 *
9 * - Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * - Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * - The name of the author may not be used to endorse or promote products
15 * derived from this software without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29/** @addtogroup genericproc
30 * @{
31 */
32
33/**
34 * @file
35 * @brief Scheduler and load balancing.
36 *
37 * This file contains the scheduler and kcpulb kernel thread which
38 * performs load-balancing of per-CPU run queues.
39 */
40
41#include <proc/scheduler.h>
42#include <proc/thread.h>
43#include <proc/task.h>
44#include <mm/frame.h>
45#include <mm/page.h>
46#include <mm/as.h>
47#include <time/timeout.h>
48#include <time/delay.h>
49#include <arch/asm.h>
50#include <arch/faddr.h>
51#include <arch/cycle.h>
52#include <atomic.h>
53#include <synch/spinlock.h>
54#include <config.h>
55#include <context.h>
56#include <fpu_context.h>
57#include <func.h>
58#include <arch.h>
59#include <adt/list.h>
60#include <panic.h>
61#include <cpu.h>
62#include <print.h>
63#include <debug.h>
64
65static void before_task_runs(void);
66static void before_thread_runs(void);
67static void after_thread_ran(void);
68static void scheduler_separated_stack(void);
69
70atomic_t nrdy; /**< Number of ready threads in the system. */
71
72/** Carry out actions before new task runs. */
73void before_task_runs(void)
74{
75 before_task_runs_arch();
76}
77
78/** Take actions before new thread runs.
79 *
80 * Perform actions that need to be
81 * taken before the newly selected
82 * tread is passed control.
83 *
84 * THREAD->lock is locked on entry
85 *
86 */
87void before_thread_runs(void)
88{
89 before_thread_runs_arch();
90#ifdef CONFIG_FPU_LAZY
91 if(THREAD == CPU->fpu_owner)
92 fpu_enable();
93 else
94 fpu_disable();
95#else
96 fpu_enable();
97 if (THREAD->fpu_context_exists)
98 fpu_context_restore(THREAD->saved_fpu_context);
99 else {
100 fpu_init();
101 THREAD->fpu_context_exists = 1;
102 }
103#endif
104}
105
106/** Take actions after THREAD had run.
107 *
108 * Perform actions that need to be
109 * taken after the running thread
110 * had been preempted by the scheduler.
111 *
112 * THREAD->lock is locked on entry
113 *
114 */
115void after_thread_ran(void)
116{
117 after_thread_ran_arch();
118}
119
120#ifdef CONFIG_FPU_LAZY
121void scheduler_fpu_lazy_request(void)
122{
123restart:
124 fpu_enable();
125 spinlock_lock(&CPU->lock);
126
127 /* Save old context */
128 if (CPU->fpu_owner != NULL) {
129 spinlock_lock(&CPU->fpu_owner->lock);
130 fpu_context_save(CPU->fpu_owner->saved_fpu_context);
131 /* don't prevent migration */
132 CPU->fpu_owner->fpu_context_engaged = 0;
133 spinlock_unlock(&CPU->fpu_owner->lock);
134 CPU->fpu_owner = NULL;
135 }
136
137 spinlock_lock(&THREAD->lock);
138 if (THREAD->fpu_context_exists) {
139 fpu_context_restore(THREAD->saved_fpu_context);
140 } else {
141 /* Allocate FPU context */
142 if (!THREAD->saved_fpu_context) {
143 /* Might sleep */
144 spinlock_unlock(&THREAD->lock);
145 spinlock_unlock(&CPU->lock);
146 THREAD->saved_fpu_context =
147 (fpu_context_t *) slab_alloc(fpu_context_slab, 0);
148 /* We may have switched CPUs during slab_alloc */
149 goto restart;
150 }
151 fpu_init();
152 THREAD->fpu_context_exists = 1;
153 }
154 CPU->fpu_owner = THREAD;
155 THREAD->fpu_context_engaged = 1;
156 spinlock_unlock(&THREAD->lock);
157
158 spinlock_unlock(&CPU->lock);
159}
160#endif
161
162/** Initialize scheduler
163 *
164 * Initialize kernel scheduler.
165 *
166 */
167void scheduler_init(void)
168{
169}
170
171/** Get thread to be scheduled
172 *
173 * Get the optimal thread to be scheduled
174 * according to thread accounting and scheduler
175 * policy.
176 *
177 * @return Thread to be scheduled.
178 *
179 */
180static thread_t *find_best_thread(void)
181{
182 thread_t *t;
183 runq_t *r;
184 int i;
185
186 ASSERT(CPU != NULL);
187
188loop:
189 interrupts_enable();
190
191 if (atomic_get(&CPU->nrdy) == 0) {
192 /*
193 * For there was nothing to run, the CPU goes to sleep
194 * until a hardware interrupt or an IPI comes.
195 * This improves energy saving and hyperthreading.
196 */
197
198 /*
199 * An interrupt might occur right now and wake up a thread.
200 * In such case, the CPU will continue to go to sleep
201 * even though there is a runnable thread.
202 */
203
204 cpu_sleep();
205 goto loop;
206 }
207
208 interrupts_disable();
209
210 for (i = 0; i < RQ_COUNT; i++) {
211 r = &CPU->rq[i];
212 spinlock_lock(&r->lock);
213 if (r->n == 0) {
214 /*
215 * If this queue is empty, try a lower-priority queue.
216 */
217 spinlock_unlock(&r->lock);
218 continue;
219 }
220
221 atomic_dec(&CPU->nrdy);
222 atomic_dec(&nrdy);
223 r->n--;
224
225 /*
226 * Take the first thread from the queue.
227 */
228 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
229 list_remove(&t->rq_link);
230
231 spinlock_unlock(&r->lock);
232
233 spinlock_lock(&t->lock);
234 t->cpu = CPU;
235
236 t->ticks = us2ticks((i + 1) * 10000);
237 t->priority = i; /* correct rq index */
238
239 /*
240 * Clear the THREAD_FLAG_STOLEN flag so that t can be migrated
241 * when load balancing needs emerge.
242 */
243 t->flags &= ~THREAD_FLAG_STOLEN;
244 spinlock_unlock(&t->lock);
245
246 return t;
247 }
248 goto loop;
249
250}
251
252/** Prevent rq starvation
253 *
254 * Prevent low priority threads from starving in rq's.
255 *
256 * When the function decides to relink rq's, it reconnects
257 * respective pointers so that in result threads with 'pri'
258 * greater or equal start are moved to a higher-priority queue.
259 *
260 * @param start Threshold priority.
261 *
262 */
263static void relink_rq(int start)
264{
265 link_t head;
266 runq_t *r;
267 int i, n;
268
269 list_initialize(&head);
270 spinlock_lock(&CPU->lock);
271 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
272 for (i = start; i < RQ_COUNT - 1; i++) {
273 /* remember and empty rq[i + 1] */
274 r = &CPU->rq[i + 1];
275 spinlock_lock(&r->lock);
276 list_concat(&head, &r->rq_head);
277 n = r->n;
278 r->n = 0;
279 spinlock_unlock(&r->lock);
280
281 /* append rq[i + 1] to rq[i] */
282 r = &CPU->rq[i];
283 spinlock_lock(&r->lock);
284 list_concat(&r->rq_head, &head);
285 r->n += n;
286 spinlock_unlock(&r->lock);
287 }
288 CPU->needs_relink = 0;
289 }
290 spinlock_unlock(&CPU->lock);
291
292}
293
294/** The scheduler
295 *
296 * The thread scheduling procedure.
297 * Passes control directly to
298 * scheduler_separated_stack().
299 *
300 */
301void scheduler(void)
302{
303 volatile ipl_t ipl;
304
305 ASSERT(CPU != NULL);
306
307 ipl = interrupts_disable();
308
309 if (atomic_get(&haltstate))
310 halt();
311
312 if (THREAD) {
313 spinlock_lock(&THREAD->lock);
314
315 /* Update thread accounting */
316 THREAD->cycles += get_cycle() - THREAD->last_cycle;
317
318#ifndef CONFIG_FPU_LAZY
319 fpu_context_save(THREAD->saved_fpu_context);
320#endif
321 if (!context_save(&THREAD->saved_context)) {
322 /*
323 * This is the place where threads leave scheduler();
324 */
325
326 /* Save current CPU cycle */
327 THREAD->last_cycle = get_cycle();
328
329 spinlock_unlock(&THREAD->lock);
330 interrupts_restore(THREAD->saved_context.ipl);
331
332 return;
333 }
334
335 /*
336 * Interrupt priority level of preempted thread is recorded
337 * here to facilitate scheduler() invocations from
338 * interrupts_disable()'d code (e.g. waitq_sleep_timeout()).
339 */
340 THREAD->saved_context.ipl = ipl;
341 }
342
343 /*
344 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
345 * and preemption counter. At this point THE could be coming either
346 * from THREAD's or CPU's stack.
347 */
348 the_copy(THE, (the_t *) CPU->stack);
349
350 /*
351 * We may not keep the old stack.
352 * Reason: If we kept the old stack and got blocked, for instance, in
353 * find_best_thread(), the old thread could get rescheduled by another
354 * CPU and overwrite the part of its own stack that was also used by
355 * the scheduler on this CPU.
356 *
357 * Moreover, we have to bypass the compiler-generated POP sequence
358 * which is fooled by SP being set to the very top of the stack.
359 * Therefore the scheduler() function continues in
360 * scheduler_separated_stack().
361 */
362 context_save(&CPU->saved_context);
363 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack),
364 (uintptr_t) CPU->stack, CPU_STACK_SIZE);
365 context_restore(&CPU->saved_context);
366 /* not reached */
367}
368
369/** Scheduler stack switch wrapper
370 *
371 * Second part of the scheduler() function
372 * using new stack. Handling the actual context
373 * switch to a new thread.
374 *
375 * Assume THREAD->lock is held.
376 */
377void scheduler_separated_stack(void)
378{
379 int priority;
380 DEADLOCK_PROBE_INIT(p_joinwq);
381
382 ASSERT(CPU != NULL);
383
384 if (THREAD) {
385 /* must be run after the switch to scheduler stack */
386 after_thread_ran();
387
388 switch (THREAD->state) {
389 case Running:
390 spinlock_unlock(&THREAD->lock);
391 thread_ready(THREAD);
392 break;
393
394 case Exiting:
395repeat:
396 if (THREAD->detached) {
397 thread_destroy(THREAD);
398 } else {
399 /*
400 * The thread structure is kept allocated until
401 * somebody calls thread_detach() on it.
402 */
403 if (!spinlock_trylock(&THREAD->join_wq.lock)) {
404 /*
405 * Avoid deadlock.
406 */
407 spinlock_unlock(&THREAD->lock);
408 delay(HZ);
409 spinlock_lock(&THREAD->lock);
410 DEADLOCK_PROBE(p_joinwq,
411 DEADLOCK_THRESHOLD);
412 goto repeat;
413 }
414 _waitq_wakeup_unsafe(&THREAD->join_wq,
415 WAKEUP_FIRST);
416 spinlock_unlock(&THREAD->join_wq.lock);
417
418 THREAD->state = Lingering;
419 spinlock_unlock(&THREAD->lock);
420 }
421 break;
422
423 case Sleeping:
424 /*
425 * Prefer the thread after it's woken up.
426 */
427 THREAD->priority = -1;
428
429 /*
430 * We need to release wq->lock which we locked in
431 * waitq_sleep(). Address of wq->lock is kept in
432 * THREAD->sleep_queue.
433 */
434 spinlock_unlock(&THREAD->sleep_queue->lock);
435
436 /*
437 * Check for possible requests for out-of-context
438 * invocation.
439 */
440 if (THREAD->call_me) {
441 THREAD->call_me(THREAD->call_me_with);
442 THREAD->call_me = NULL;
443 THREAD->call_me_with = NULL;
444 }
445
446 spinlock_unlock(&THREAD->lock);
447
448 break;
449
450 default:
451 /*
452 * Entering state is unexpected.
453 */
454 panic("tid%llu: unexpected state %s\n", THREAD->tid,
455 thread_states[THREAD->state]);
456 break;
457 }
458
459 THREAD = NULL;
460 }
461
462 THREAD = find_best_thread();
463
464 spinlock_lock(&THREAD->lock);
465 priority = THREAD->priority;
466 spinlock_unlock(&THREAD->lock);
467
468 relink_rq(priority);
469
470 /*
471 * If both the old and the new task are the same, lots of work is
472 * avoided.
473 */
474 if (TASK != THREAD->task) {
475 as_t *as1 = NULL;
476 as_t *as2;
477
478 if (TASK) {
479 spinlock_lock(&TASK->lock);
480 as1 = TASK->as;
481 spinlock_unlock(&TASK->lock);
482 }
483
484 spinlock_lock(&THREAD->task->lock);
485 as2 = THREAD->task->as;
486 spinlock_unlock(&THREAD->task->lock);
487
488 /*
489 * Note that it is possible for two tasks to share one address
490 * space.
491 */
492 if (as1 != as2) {
493 /*
494 * Both tasks and address spaces are different.
495 * Replace the old one with the new one.
496 */
497 as_switch(as1, as2);
498 }
499 TASK = THREAD->task;
500 before_task_runs();
501 }
502
503 spinlock_lock(&THREAD->lock);
504 THREAD->state = Running;
505
506#ifdef SCHEDULER_VERBOSE
507 printf("cpu%d: tid %llu (priority=%d, ticks=%llu, nrdy=%ld)\n",
508 CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks,
509 atomic_get(&CPU->nrdy));
510#endif
511
512 /*
513 * Some architectures provide late kernel PA2KA(identity)
514 * mapping in a page fault handler. However, the page fault
515 * handler uses the kernel stack of the running thread and
516 * therefore cannot be used to map it. The kernel stack, if
517 * necessary, is to be mapped in before_thread_runs(). This
518 * function must be executed before the switch to the new stack.
519 */
520 before_thread_runs();
521
522 /*
523 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to
524 * thread's stack.
525 */
526 the_copy(THE, (the_t *) THREAD->kstack);
527
528 context_restore(&THREAD->saved_context);
529 /* not reached */
530}
531
532#ifdef CONFIG_SMP
533/** Load balancing thread
534 *
535 * SMP load balancing thread, supervising thread supplies
536 * for the CPU it's wired to.
537 *
538 * @param arg Generic thread argument (unused).
539 *
540 */
541void kcpulb(void *arg)
542{
543 thread_t *t;
544 int count, average, j, k = 0;
545 unsigned int i;
546 ipl_t ipl;
547
548 /*
549 * Detach kcpulb as nobody will call thread_join_timeout() on it.
550 */
551 thread_detach(THREAD);
552
553loop:
554 /*
555 * Work in 1s intervals.
556 */
557 thread_sleep(1);
558
559not_satisfied:
560 /*
561 * Calculate the number of threads that will be migrated/stolen from
562 * other CPU's. Note that situation can have changed between two
563 * passes. Each time get the most up to date counts.
564 */
565 average = atomic_get(&nrdy) / config.cpu_active + 1;
566 count = average - atomic_get(&CPU->nrdy);
567
568 if (count <= 0)
569 goto satisfied;
570
571 /*
572 * Searching least priority queues on all CPU's first and most priority
573 * queues on all CPU's last.
574 */
575 for (j = RQ_COUNT - 1; j >= 0; j--) {
576 for (i = 0; i < config.cpu_active; i++) {
577 link_t *l;
578 runq_t *r;
579 cpu_t *cpu;
580
581 cpu = &cpus[(i + k) % config.cpu_active];
582
583 /*
584 * Not interested in ourselves.
585 * Doesn't require interrupt disabling for kcpulb has
586 * THREAD_FLAG_WIRED.
587 */
588 if (CPU == cpu)
589 continue;
590 if (atomic_get(&cpu->nrdy) <= average)
591 continue;
592
593 ipl = interrupts_disable();
594 r = &cpu->rq[j];
595 spinlock_lock(&r->lock);
596 if (r->n == 0) {
597 spinlock_unlock(&r->lock);
598 interrupts_restore(ipl);
599 continue;
600 }
601
602 t = NULL;
603 l = r->rq_head.prev; /* search rq from the back */
604 while (l != &r->rq_head) {
605 t = list_get_instance(l, thread_t, rq_link);
606 /*
607 * We don't want to steal CPU-wired threads
608 * neither threads already stolen. The latter
609 * prevents threads from migrating between CPU's
610 * without ever being run. We don't want to
611 * steal threads whose FPU context is still in
612 * CPU.
613 */
614 spinlock_lock(&t->lock);
615 if ((!(t->flags & (THREAD_FLAG_WIRED |
616 THREAD_FLAG_STOLEN))) &&
617 (!(t->fpu_context_engaged))) {
618 /*
619 * Remove t from r.
620 */
621 spinlock_unlock(&t->lock);
622
623 atomic_dec(&cpu->nrdy);
624 atomic_dec(&nrdy);
625
626 r->n--;
627 list_remove(&t->rq_link);
628
629 break;
630 }
631 spinlock_unlock(&t->lock);
632 l = l->prev;
633 t = NULL;
634 }
635 spinlock_unlock(&r->lock);
636
637 if (t) {
638 /*
639 * Ready t on local CPU
640 */
641 spinlock_lock(&t->lock);
642#ifdef KCPULB_VERBOSE
643 printf("kcpulb%d: TID %llu -> cpu%d, nrdy=%ld, "
644 "avg=%nd\n", CPU->id, t->tid, CPU->id,
645 atomic_get(&CPU->nrdy),
646 atomic_get(&nrdy) / config.cpu_active);
647#endif
648 t->flags |= THREAD_FLAG_STOLEN;
649 t->state = Entering;
650 spinlock_unlock(&t->lock);
651
652 thread_ready(t);
653
654 interrupts_restore(ipl);
655
656 if (--count == 0)
657 goto satisfied;
658
659 /*
660 * We are not satisfied yet, focus on another
661 * CPU next time.
662 */
663 k++;
664
665 continue;
666 }
667 interrupts_restore(ipl);
668 }
669 }
670
671 if (atomic_get(&CPU->nrdy)) {
672 /*
673 * Be a little bit light-weight and let migrated threads run.
674 */
675 scheduler();
676 } else {
677 /*
678 * We failed to migrate a single thread.
679 * Give up this turn.
680 */
681 goto loop;
682 }
683
684 goto not_satisfied;
685
686satisfied:
687 goto loop;
688}
689
690#endif /* CONFIG_SMP */
691
692
693/** Print information about threads & scheduler queues */
694void sched_print_list(void)
695{
696 ipl_t ipl;
697 unsigned int cpu, i;
698 runq_t *r;
699 thread_t *t;
700 link_t *cur;
701
702 /* We are going to mess with scheduler structures,
703 * let's not be interrupted */
704 ipl = interrupts_disable();
705 for (cpu = 0; cpu < config.cpu_count; cpu++) {
706
707 if (!cpus[cpu].active)
708 continue;
709
710 spinlock_lock(&cpus[cpu].lock);
711 printf("cpu%d: address=%p, nrdy=%ld, needs_relink=%ld\n",
712 cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy),
713 cpus[cpu].needs_relink);
714
715 for (i = 0; i < RQ_COUNT; i++) {
716 r = &cpus[cpu].rq[i];
717 spinlock_lock(&r->lock);
718 if (!r->n) {
719 spinlock_unlock(&r->lock);
720 continue;
721 }
722 printf("\trq[%d]: ", i);
723 for (cur = r->rq_head.next; cur != &r->rq_head;
724 cur = cur->next) {
725 t = list_get_instance(cur, thread_t, rq_link);
726 printf("%llu(%s) ", t->tid,
727 thread_states[t->state]);
728 }
729 printf("\n");
730 spinlock_unlock(&r->lock);
731 }
732 spinlock_unlock(&cpus[cpu].lock);
733 }
734
735 interrupts_restore(ipl);
736}
737
738/** @}
739 */
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