source: mainline/kernel/generic/src/proc/scheduler.c@ 2d3ddad

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 2d3ddad was 2d3ddad, checked in by Jakub Jermar <jakub@…>, 15 years ago

Add more *_locked() assertions.
  • Property mode set to 100644
File size: 17.8 KB
Line 
1/*
2 * Copyright (c) 2010 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 irq_spinlock_lock(&CPU->lock, false);
126
127 /* Save old context */
128 if (CPU->fpu_owner != NULL) {
129 irq_spinlock_lock(&CPU->fpu_owner->lock, false);
130 fpu_context_save(CPU->fpu_owner->saved_fpu_context);
131
132 /* Don't prevent migration */
133 CPU->fpu_owner->fpu_context_engaged = 0;
134 irq_spinlock_unlock(&CPU->fpu_owner->lock, false);
135 CPU->fpu_owner = NULL;
136 }
137
138 irq_spinlock_lock(&THREAD->lock, false);
139 if (THREAD->fpu_context_exists) {
140 fpu_context_restore(THREAD->saved_fpu_context);
141 } else {
142 /* Allocate FPU context */
143 if (!THREAD->saved_fpu_context) {
144 /* Might sleep */
145 irq_spinlock_unlock(&THREAD->lock, false);
146 irq_spinlock_unlock(&CPU->lock, false);
147 THREAD->saved_fpu_context =
148 (fpu_context_t *) slab_alloc(fpu_context_slab, 0);
149
150 /* We may have switched CPUs during slab_alloc */
151 goto restart;
152 }
153 fpu_init();
154 THREAD->fpu_context_exists = 1;
155 }
156
157 CPU->fpu_owner = THREAD;
158 THREAD->fpu_context_engaged = 1;
159 irq_spinlock_unlock(&THREAD->lock, false);
160
161 irq_spinlock_unlock(&CPU->lock, false);
162}
163#endif /* CONFIG_FPU_LAZY */
164
165/** Initialize scheduler
166 *
167 * Initialize kernel scheduler.
168 *
169 */
170void scheduler_init(void)
171{
172}
173
174/** Get thread to be scheduled
175 *
176 * Get the optimal thread to be scheduled
177 * according to thread accounting and scheduler
178 * policy.
179 *
180 * @return Thread to be scheduled.
181 *
182 */
183static thread_t *find_best_thread(void)
184{
185 ASSERT(CPU != NULL);
186
187loop:
188
189 if (atomic_get(&CPU->nrdy) == 0) {
190 /*
191 * For there was nothing to run, the CPU goes to sleep
192 * until a hardware interrupt or an IPI comes.
193 * This improves energy saving and hyperthreading.
194 */
195
196 /* Mark CPU as it was idle this clock tick */
197 irq_spinlock_lock(&CPU->lock, false);
198 CPU->idle = true;
199 irq_spinlock_unlock(&CPU->lock, false);
200
201 interrupts_enable();
202 /*
203 * An interrupt might occur right now and wake up a thread.
204 * In such case, the CPU will continue to go to sleep
205 * even though there is a runnable thread.
206 */
207 cpu_sleep();
208 interrupts_disable();
209 goto loop;
210 }
211
212 unsigned int i;
213 for (i = 0; i < RQ_COUNT; i++) {
214 irq_spinlock_lock(&(CPU->rq[i].lock), false);
215 if (CPU->rq[i].n == 0) {
216 /*
217 * If this queue is empty, try a lower-priority queue.
218 */
219 irq_spinlock_unlock(&(CPU->rq[i].lock), false);
220 continue;
221 }
222
223 atomic_dec(&CPU->nrdy);
224 atomic_dec(&nrdy);
225 CPU->rq[i].n--;
226
227 /*
228 * Take the first thread from the queue.
229 */
230 thread_t *thread =
231 list_get_instance(CPU->rq[i].rq_head.next, thread_t, rq_link);
232 list_remove(&thread->rq_link);
233
234 irq_spinlock_pass(&(CPU->rq[i].lock), &thread->lock);
235
236 thread->cpu = CPU;
237 thread->ticks = us2ticks((i + 1) * 10000);
238 thread->priority = i; /* Correct rq index */
239
240 /*
241 * Clear the THREAD_FLAG_STOLEN flag so that t can be migrated
242 * when load balancing needs emerge.
243 */
244 thread->flags &= ~THREAD_FLAG_STOLEN;
245 irq_spinlock_unlock(&thread->lock, false);
246
247 return thread;
248 }
249
250 goto loop;
251}
252
253/** Prevent rq starvation
254 *
255 * Prevent low priority threads from starving in rq's.
256 *
257 * When the function decides to relink rq's, it reconnects
258 * respective pointers so that in result threads with 'pri'
259 * greater or equal start are moved to a higher-priority queue.
260 *
261 * @param start Threshold priority.
262 *
263 */
264static void relink_rq(int start)
265{
266 link_t head;
267
268 list_initialize(&head);
269 irq_spinlock_lock(&CPU->lock, false);
270
271 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
272 int i;
273 for (i = start; i < RQ_COUNT - 1; i++) {
274 /* Remember and empty rq[i + 1] */
275
276 irq_spinlock_lock(&CPU->rq[i + 1].lock, false);
277 list_concat(&head, &CPU->rq[i + 1].rq_head);
278 size_t n = CPU->rq[i + 1].n;
279 CPU->rq[i + 1].n = 0;
280 irq_spinlock_unlock(&CPU->rq[i + 1].lock, false);
281
282 /* Append rq[i + 1] to rq[i] */
283
284 irq_spinlock_lock(&CPU->rq[i].lock, false);
285 list_concat(&CPU->rq[i].rq_head, &head);
286 CPU->rq[i].n += n;
287 irq_spinlock_unlock(&CPU->rq[i].lock, false);
288 }
289
290 CPU->needs_relink = 0;
291 }
292
293 irq_spinlock_unlock(&CPU->lock, false);
294}
295
296/** The scheduler
297 *
298 * The thread scheduling procedure.
299 * Passes control directly to
300 * scheduler_separated_stack().
301 *
302 */
303void scheduler(void)
304{
305 volatile ipl_t ipl;
306
307 ASSERT(CPU != NULL);
308
309 ipl = interrupts_disable();
310
311 if (atomic_get(&haltstate))
312 halt();
313
314 if (THREAD) {
315 irq_spinlock_lock(&THREAD->lock, false);
316
317 /* Update thread kernel accounting */
318 THREAD->kcycles += get_cycle() - THREAD->last_cycle;
319
320#ifndef CONFIG_FPU_LAZY
321 fpu_context_save(THREAD->saved_fpu_context);
322#endif
323 if (!context_save(&THREAD->saved_context)) {
324 /*
325 * This is the place where threads leave scheduler();
326 */
327
328 /* Save current CPU cycle */
329 THREAD->last_cycle = get_cycle();
330
331 irq_spinlock_unlock(&THREAD->lock, false);
332 interrupts_restore(THREAD->saved_context.ipl);
333
334 return;
335 }
336
337 /*
338 * Interrupt priority level of preempted thread is recorded
339 * here to facilitate scheduler() invocations from
340 * interrupts_disable()'d code (e.g. waitq_sleep_timeout()).
341 *
342 */
343 THREAD->saved_context.ipl = ipl;
344 }
345
346 /*
347 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
348 * and preemption counter. At this point THE could be coming either
349 * from THREAD's or CPU's stack.
350 *
351 */
352 the_copy(THE, (the_t *) CPU->stack);
353
354 /*
355 * We may not keep the old stack.
356 * Reason: If we kept the old stack and got blocked, for instance, in
357 * find_best_thread(), the old thread could get rescheduled by another
358 * CPU and overwrite the part of its own stack that was also used by
359 * the scheduler on this CPU.
360 *
361 * Moreover, we have to bypass the compiler-generated POP sequence
362 * which is fooled by SP being set to the very top of the stack.
363 * Therefore the scheduler() function continues in
364 * scheduler_separated_stack().
365 *
366 */
367 context_save(&CPU->saved_context);
368 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack),
369 (uintptr_t) CPU->stack, CPU_STACK_SIZE);
370 context_restore(&CPU->saved_context);
371
372 /* Not reached */
373}
374
375/** Scheduler stack switch wrapper
376 *
377 * Second part of the scheduler() function
378 * using new stack. Handling the actual context
379 * switch to a new thread.
380 *
381 */
382void scheduler_separated_stack(void)
383{
384 DEADLOCK_PROBE_INIT(p_joinwq);
385 task_t *old_task = TASK;
386 as_t *old_as = AS;
387
388 ASSERT(!THREAD || irq_spinlock_locked(&THREAD->lock));
389 ASSERT(CPU != NULL);
390
391 /*
392 * Hold the current task and the address space to prevent their
393 * possible destruction should thread_destroy() be called on this or any
394 * other processor while the scheduler is still using them.
395 *
396 */
397 if (old_task)
398 task_hold(old_task);
399
400 if (old_as)
401 as_hold(old_as);
402
403 if (THREAD) {
404 /* Must be run after the switch to scheduler stack */
405 after_thread_ran();
406
407 switch (THREAD->state) {
408 case Running:
409 irq_spinlock_unlock(&THREAD->lock, false);
410 thread_ready(THREAD);
411 break;
412
413 case Exiting:
414repeat:
415 if (THREAD->detached) {
416 thread_destroy(THREAD, false);
417 } else {
418 /*
419 * The thread structure is kept allocated until
420 * somebody calls thread_detach() on it.
421 *
422 */
423 if (!irq_spinlock_trylock(&THREAD->join_wq.lock)) {
424 /*
425 * Avoid deadlock.
426 *
427 */
428 irq_spinlock_unlock(&THREAD->lock, false);
429 delay(HZ);
430 irq_spinlock_lock(&THREAD->lock, false);
431 DEADLOCK_PROBE(p_joinwq,
432 DEADLOCK_THRESHOLD);
433 goto repeat;
434 }
435 _waitq_wakeup_unsafe(&THREAD->join_wq,
436 WAKEUP_FIRST);
437 irq_spinlock_unlock(&THREAD->join_wq.lock, false);
438
439 THREAD->state = Lingering;
440 irq_spinlock_unlock(&THREAD->lock, false);
441 }
442 break;
443
444 case Sleeping:
445 /*
446 * Prefer the thread after it's woken up.
447 *
448 */
449 THREAD->priority = -1;
450
451 /*
452 * We need to release wq->lock which we locked in
453 * waitq_sleep(). Address of wq->lock is kept in
454 * THREAD->sleep_queue.
455 *
456 */
457 irq_spinlock_unlock(&THREAD->sleep_queue->lock, false);
458
459 /*
460 * Check for possible requests for out-of-context
461 * invocation.
462 *
463 */
464 if (THREAD->call_me) {
465 THREAD->call_me(THREAD->call_me_with);
466 THREAD->call_me = NULL;
467 THREAD->call_me_with = NULL;
468 }
469
470 irq_spinlock_unlock(&THREAD->lock, false);
471
472 break;
473
474 default:
475 /*
476 * Entering state is unexpected.
477 *
478 */
479 panic("tid%" PRIu64 ": unexpected state %s.",
480 THREAD->tid, thread_states[THREAD->state]);
481 break;
482 }
483
484 THREAD = NULL;
485 }
486
487 THREAD = find_best_thread();
488
489 irq_spinlock_lock(&THREAD->lock, false);
490 int priority = THREAD->priority;
491 irq_spinlock_unlock(&THREAD->lock, false);
492
493 relink_rq(priority);
494
495 /*
496 * If both the old and the new task are the same, lots of work is
497 * avoided.
498 *
499 */
500 if (TASK != THREAD->task) {
501 as_t *new_as = THREAD->task->as;
502
503 /*
504 * Note that it is possible for two tasks to share one address
505 * space.
506 (
507 */
508 if (old_as != new_as) {
509 /*
510 * Both tasks and address spaces are different.
511 * Replace the old one with the new one.
512 *
513 */
514 as_switch(old_as, new_as);
515 }
516
517 TASK = THREAD->task;
518 before_task_runs();
519 }
520
521 if (old_task)
522 task_release(old_task);
523
524 if (old_as)
525 as_release(old_as);
526
527 irq_spinlock_lock(&THREAD->lock, false);
528 THREAD->state = Running;
529
530#ifdef SCHEDULER_VERBOSE
531 printf("cpu%u: tid %" PRIu64 " (priority=%d, ticks=%" PRIu64
532 ", nrdy=%ld)\n", CPU->id, THREAD->tid, THREAD->priority,
533 THREAD->ticks, atomic_get(&CPU->nrdy));
534#endif
535
536 /*
537 * Some architectures provide late kernel PA2KA(identity)
538 * mapping in a page fault handler. However, the page fault
539 * handler uses the kernel stack of the running thread and
540 * therefore cannot be used to map it. The kernel stack, if
541 * necessary, is to be mapped in before_thread_runs(). This
542 * function must be executed before the switch to the new stack.
543 *
544 */
545 before_thread_runs();
546
547 /*
548 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to
549 * thread's stack.
550 *
551 */
552 the_copy(THE, (the_t *) THREAD->kstack);
553
554 context_restore(&THREAD->saved_context);
555
556 /* Not reached */
557}
558
559#ifdef CONFIG_SMP
560/** Load balancing thread
561 *
562 * SMP load balancing thread, supervising thread supplies
563 * for the CPU it's wired to.
564 *
565 * @param arg Generic thread argument (unused).
566 *
567 */
568void kcpulb(void *arg)
569{
570 atomic_count_t average;
571 atomic_count_t rdy;
572
573 /*
574 * Detach kcpulb as nobody will call thread_join_timeout() on it.
575 */
576 thread_detach(THREAD);
577
578loop:
579 /*
580 * Work in 1s intervals.
581 */
582 thread_sleep(1);
583
584not_satisfied:
585 /*
586 * Calculate the number of threads that will be migrated/stolen from
587 * other CPU's. Note that situation can have changed between two
588 * passes. Each time get the most up to date counts.
589 *
590 */
591 average = atomic_get(&nrdy) / config.cpu_active + 1;
592 rdy = atomic_get(&CPU->nrdy);
593
594 if (average <= rdy)
595 goto satisfied;
596
597 atomic_count_t count = average - rdy;
598
599 /*
600 * Searching least priority queues on all CPU's first and most priority
601 * queues on all CPU's last.
602 *
603 */
604 size_t acpu;
605 size_t acpu_bias = 0;
606 int rq;
607
608 for (rq = RQ_COUNT - 1; rq >= 0; rq--) {
609 for (acpu = 0; acpu < config.cpu_active; acpu++) {
610 cpu_t *cpu = &cpus[(acpu + acpu_bias) % config.cpu_active];
611
612 /*
613 * Not interested in ourselves.
614 * Doesn't require interrupt disabling for kcpulb has
615 * THREAD_FLAG_WIRED.
616 *
617 */
618 if (CPU == cpu)
619 continue;
620
621 if (atomic_get(&cpu->nrdy) <= average)
622 continue;
623
624 irq_spinlock_lock(&(cpu->rq[rq].lock), true);
625 if (cpu->rq[rq].n == 0) {
626 irq_spinlock_unlock(&(cpu->rq[rq].lock), true);
627 continue;
628 }
629
630 thread_t *thread = NULL;
631
632 /* Search rq from the back */
633 link_t *link = cpu->rq[rq].rq_head.prev;
634
635 while (link != &(cpu->rq[rq].rq_head)) {
636 thread = (thread_t *) list_get_instance(link, thread_t, rq_link);
637
638 /*
639 * We don't want to steal CPU-wired threads
640 * neither threads already stolen. The latter
641 * prevents threads from migrating between CPU's
642 * without ever being run. We don't want to
643 * steal threads whose FPU context is still in
644 * CPU.
645 *
646 */
647 irq_spinlock_lock(&thread->lock, false);
648
649 if ((!(thread->flags & (THREAD_FLAG_WIRED | THREAD_FLAG_STOLEN)))
650 && (!(thread->fpu_context_engaged))) {
651 /*
652 * Remove thread from ready queue.
653 */
654 irq_spinlock_unlock(&thread->lock, false);
655
656 atomic_dec(&cpu->nrdy);
657 atomic_dec(&nrdy);
658
659 cpu->rq[rq].n--;
660 list_remove(&thread->rq_link);
661
662 break;
663 }
664
665 irq_spinlock_unlock(&thread->lock, false);
666
667 link = link->prev;
668 thread = NULL;
669 }
670
671 if (thread) {
672 /*
673 * Ready thread on local CPU
674 *
675 */
676
677 irq_spinlock_pass(&(cpu->rq[rq].lock), &thread->lock);
678
679#ifdef KCPULB_VERBOSE
680 printf("kcpulb%u: TID %" PRIu64 " -> cpu%u, "
681 "nrdy=%ld, avg=%ld\n", CPU->id, t->tid,
682 CPU->id, atomic_get(&CPU->nrdy),
683 atomic_get(&nrdy) / config.cpu_active);
684#endif
685
686 thread->flags |= THREAD_FLAG_STOLEN;
687 thread->state = Entering;
688
689 irq_spinlock_unlock(&thread->lock, true);
690 thread_ready(thread);
691
692 if (--count == 0)
693 goto satisfied;
694
695 /*
696 * We are not satisfied yet, focus on another
697 * CPU next time.
698 *
699 */
700 acpu_bias++;
701
702 continue;
703 } else
704 irq_spinlock_unlock(&(cpu->rq[rq].lock), true);
705
706 }
707 }
708
709 if (atomic_get(&CPU->nrdy)) {
710 /*
711 * Be a little bit light-weight and let migrated threads run.
712 *
713 */
714 scheduler();
715 } else {
716 /*
717 * We failed to migrate a single thread.
718 * Give up this turn.
719 *
720 */
721 goto loop;
722 }
723
724 goto not_satisfied;
725
726satisfied:
727 goto loop;
728}
729#endif /* CONFIG_SMP */
730
731/** Print information about threads & scheduler queues
732 *
733 */
734void sched_print_list(void)
735{
736 size_t cpu;
737 for (cpu = 0; cpu < config.cpu_count; cpu++) {
738 if (!cpus[cpu].active)
739 continue;
740
741 irq_spinlock_lock(&cpus[cpu].lock, true);
742
743 printf("cpu%u: address=%p, nrdy=%ld, needs_relink=%" PRIs "\n",
744 cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy),
745 cpus[cpu].needs_relink);
746
747 unsigned int i;
748 for (i = 0; i < RQ_COUNT; i++) {
749 irq_spinlock_lock(&(cpus[cpu].rq[i].lock), false);
750 if (cpus[cpu].rq[i].n == 0) {
751 irq_spinlock_unlock(&(cpus[cpu].rq[i].lock), false);
752 continue;
753 }
754
755 printf("\trq[%u]: ", i);
756 link_t *cur;
757 for (cur = cpus[cpu].rq[i].rq_head.next;
758 cur != &(cpus[cpu].rq[i].rq_head);
759 cur = cur->next) {
760 thread_t *thread = list_get_instance(cur, thread_t, rq_link);
761 printf("%" PRIu64 "(%s) ", thread->tid,
762 thread_states[thread->state]);
763 }
764 printf("\n");
765
766 irq_spinlock_unlock(&(cpus[cpu].rq[i].lock), false);
767 }
768
769 irq_spinlock_unlock(&cpus[cpu].lock, true);
770 }
771}
772
773/** @}
774 */
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