source: mainline/kernel/generic/src/proc/scheduler.c@ ea63704

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since ea63704 was ea63704, checked in by Jakub Jermar <jakub@…>, 18 years ago

Formatting and indentation fixes.
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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(10);
409 spinlock_lock(&THREAD->lock);
410 DEADLOCK_PROBE(p_joinwq,
411 DEADLOCK_THRESHOLD);
412 goto repeat;
413 }
414 _waitq_wakeup_unsafe(&THREAD->join_wq, false);
415 spinlock_unlock(&THREAD->join_wq.lock);
416
417 THREAD->state = Undead;
418 spinlock_unlock(&THREAD->lock);
419 }
420 break;
421
422 case Sleeping:
423 /*
424 * Prefer the thread after it's woken up.
425 */
426 THREAD->priority = -1;
427
428 /*
429 * We need to release wq->lock which we locked in
430 * waitq_sleep(). Address of wq->lock is kept in
431 * THREAD->sleep_queue.
432 */
433 spinlock_unlock(&THREAD->sleep_queue->lock);
434
435 /*
436 * Check for possible requests for out-of-context
437 * invocation.
438 */
439 if (THREAD->call_me) {
440 THREAD->call_me(THREAD->call_me_with);
441 THREAD->call_me = NULL;
442 THREAD->call_me_with = NULL;
443 }
444
445 spinlock_unlock(&THREAD->lock);
446
447 break;
448
449 default:
450 /*
451 * Entering state is unexpected.
452 */
453 panic("tid%llu: unexpected state %s\n", THREAD->tid,
454 thread_states[THREAD->state]);
455 break;
456 }
457
458 THREAD = NULL;
459 }
460
461 THREAD = find_best_thread();
462
463 spinlock_lock(&THREAD->lock);
464 priority = THREAD->priority;
465 spinlock_unlock(&THREAD->lock);
466
467 relink_rq(priority);
468
469 /*
470 * If both the old and the new task are the same, lots of work is
471 * avoided.
472 */
473 if (TASK != THREAD->task) {
474 as_t *as1 = NULL;
475 as_t *as2;
476
477 if (TASK) {
478 spinlock_lock(&TASK->lock);
479 as1 = TASK->as;
480 spinlock_unlock(&TASK->lock);
481 }
482
483 spinlock_lock(&THREAD->task->lock);
484 as2 = THREAD->task->as;
485 spinlock_unlock(&THREAD->task->lock);
486
487 /*
488 * Note that it is possible for two tasks to share one address
489 * space.
490 */
491 if (as1 != as2) {
492 /*
493 * Both tasks and address spaces are different.
494 * Replace the old one with the new one.
495 */
496 as_switch(as1, as2);
497 }
498 TASK = THREAD->task;
499 before_task_runs();
500 }
501
502 spinlock_lock(&THREAD->lock);
503 THREAD->state = Running;
504
505#ifdef SCHEDULER_VERBOSE
506 printf("cpu%d: tid %llu (priority=%d, ticks=%llu, nrdy=%ld)\n",
507 CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks,
508 atomic_get(&CPU->nrdy));
509#endif
510
511 /*
512 * Some architectures provide late kernel PA2KA(identity)
513 * mapping in a page fault handler. However, the page fault
514 * handler uses the kernel stack of the running thread and
515 * therefore cannot be used to map it. The kernel stack, if
516 * necessary, is to be mapped in before_thread_runs(). This
517 * function must be executed before the switch to the new stack.
518 */
519 before_thread_runs();
520
521 /*
522 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to
523 * thread's stack.
524 */
525 the_copy(THE, (the_t *) THREAD->kstack);
526
527 context_restore(&THREAD->saved_context);
528 /* not reached */
529}
530
531#ifdef CONFIG_SMP
532/** Load balancing thread
533 *
534 * SMP load balancing thread, supervising thread supplies
535 * for the CPU it's wired to.
536 *
537 * @param arg Generic thread argument (unused).
538 *
539 */
540void kcpulb(void *arg)
541{
542 thread_t *t;
543 int count, average, j, k = 0;
544 unsigned int i;
545 ipl_t ipl;
546
547 /*
548 * Detach kcpulb as nobody will call thread_join_timeout() on it.
549 */
550 thread_detach(THREAD);
551
552loop:
553 /*
554 * Work in 1s intervals.
555 */
556 thread_sleep(1);
557
558not_satisfied:
559 /*
560 * Calculate the number of threads that will be migrated/stolen from
561 * other CPU's. Note that situation can have changed between two
562 * passes. Each time get the most up to date counts.
563 */
564 average = atomic_get(&nrdy) / config.cpu_active + 1;
565 count = average - atomic_get(&CPU->nrdy);
566
567 if (count <= 0)
568 goto satisfied;
569
570 /*
571 * Searching least priority queues on all CPU's first and most priority
572 * queues on all CPU's last.
573 */
574 for (j = RQ_COUNT - 1; j >= 0; j--) {
575 for (i = 0; i < config.cpu_active; i++) {
576 link_t *l;
577 runq_t *r;
578 cpu_t *cpu;
579
580 cpu = &cpus[(i + k) % config.cpu_active];
581
582 /*
583 * Not interested in ourselves.
584 * Doesn't require interrupt disabling for kcpulb has
585 * THREAD_FLAG_WIRED.
586 */
587 if (CPU == cpu)
588 continue;
589 if (atomic_get(&cpu->nrdy) <= average)
590 continue;
591
592 ipl = interrupts_disable();
593 r = &cpu->rq[j];
594 spinlock_lock(&r->lock);
595 if (r->n == 0) {
596 spinlock_unlock(&r->lock);
597 interrupts_restore(ipl);
598 continue;
599 }
600
601 t = NULL;
602 l = r->rq_head.prev; /* search rq from the back */
603 while (l != &r->rq_head) {
604 t = list_get_instance(l, thread_t, rq_link);
605 /*
606 * We don't want to steal CPU-wired threads
607 * neither threads already stolen. The latter
608 * prevents threads from migrating between CPU's
609 * without ever being run. We don't want to
610 * steal threads whose FPU context is still in
611 * CPU.
612 */
613 spinlock_lock(&t->lock);
614 if ((!(t->flags & (THREAD_FLAG_WIRED |
615 THREAD_FLAG_STOLEN))) &&
616 (!(t->fpu_context_engaged))) {
617 /*
618 * Remove t from r.
619 */
620 spinlock_unlock(&t->lock);
621
622 atomic_dec(&cpu->nrdy);
623 atomic_dec(&nrdy);
624
625 r->n--;
626 list_remove(&t->rq_link);
627
628 break;
629 }
630 spinlock_unlock(&t->lock);
631 l = l->prev;
632 t = NULL;
633 }
634 spinlock_unlock(&r->lock);
635
636 if (t) {
637 /*
638 * Ready t on local CPU
639 */
640 spinlock_lock(&t->lock);
641#ifdef KCPULB_VERBOSE
642 printf("kcpulb%d: TID %llu -> cpu%d, nrdy=%ld, "
643 "avg=%nd\n", CPU->id, t->tid, CPU->id,
644 atomic_get(&CPU->nrdy),
645 atomic_get(&nrdy) / config.cpu_active);
646#endif
647 t->flags |= THREAD_FLAG_STOLEN;
648 t->state = Entering;
649 spinlock_unlock(&t->lock);
650
651 thread_ready(t);
652
653 interrupts_restore(ipl);
654
655 if (--count == 0)
656 goto satisfied;
657
658 /*
659 * We are not satisfied yet, focus on another
660 * CPU next time.
661 */
662 k++;
663
664 continue;
665 }
666 interrupts_restore(ipl);
667 }
668 }
669
670 if (atomic_get(&CPU->nrdy)) {
671 /*
672 * Be a little bit light-weight and let migrated threads run.
673 */
674 scheduler();
675 } else {
676 /*
677 * We failed to migrate a single thread.
678 * Give up this turn.
679 */
680 goto loop;
681 }
682
683 goto not_satisfied;
684
685satisfied:
686 goto loop;
687}
688
689#endif /* CONFIG_SMP */
690
691
692/** Print information about threads & scheduler queues */
693void sched_print_list(void)
694{
695 ipl_t ipl;
696 unsigned int cpu, i;
697 runq_t *r;
698 thread_t *t;
699 link_t *cur;
700
701 /* We are going to mess with scheduler structures,
702 * let's not be interrupted */
703 ipl = interrupts_disable();
704 for (cpu = 0; cpu < config.cpu_count; cpu++) {
705
706 if (!cpus[cpu].active)
707 continue;
708
709 spinlock_lock(&cpus[cpu].lock);
710 printf("cpu%d: address=%p, nrdy=%ld, needs_relink=%ld\n",
711 cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy),
712 cpus[cpu].needs_relink);
713
714 for (i = 0; i < RQ_COUNT; i++) {
715 r = &cpus[cpu].rq[i];
716 spinlock_lock(&r->lock);
717 if (!r->n) {
718 spinlock_unlock(&r->lock);
719 continue;
720 }
721 printf("\trq[%d]: ", i);
722 for (cur = r->rq_head.next; cur != &r->rq_head;
723 cur = cur->next) {
724 t = list_get_instance(cur, thread_t, rq_link);
725 printf("%llu(%s) ", t->tid,
726 thread_states[t->state]);
727 }
728 printf("\n");
729 spinlock_unlock(&r->lock);
730 }
731 spinlock_unlock(&cpus[cpu].lock);
732 }
733
734 interrupts_restore(ipl);
735}
736
737/** @}
738 */
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