source: mainline/generic/src/proc/scheduler.c@ cf26ba9

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since cf26ba9 was cf26ba9, checked in by Jakub Jermar <jakub@…>, 19 years ago

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1/*
2 * Copyright (C) 2001-2004 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/**
30 * @file scheduler.c
31 * @brief Scheduler and load balancing.
32 *
33 * This file contains the scheduler and kcpulb kernel thread which
34 * performs load-balancing of per-CPU run queues.
35 */
36
37#include <proc/scheduler.h>
38#include <proc/thread.h>
39#include <proc/task.h>
40#include <mm/frame.h>
41#include <mm/page.h>
42#include <mm/as.h>
43#include <arch/asm.h>
44#include <arch/faddr.h>
45#include <atomic.h>
46#include <synch/spinlock.h>
47#include <config.h>
48#include <context.h>
49#include <func.h>
50#include <arch.h>
51#include <adt/list.h>
52#include <panic.h>
53#include <typedefs.h>
54#include <cpu.h>
55#include <print.h>
56#include <debug.h>
57
58static void before_task_runs(void);
59static void before_thread_runs(void);
60static void after_thread_ran(void);
61static void scheduler_separated_stack(void);
62
63atomic_t nrdy; /**< Number of ready threads in the system. */
64
65/** Carry out actions before new task runs. */
66void before_task_runs(void)
67{
68 before_task_runs_arch();
69}
70
71/** Take actions before new thread runs.
72 *
73 * Perform actions that need to be
74 * taken before the newly selected
75 * tread is passed control.
76 *
77 * THREAD->lock is locked on entry
78 *
79 */
80void before_thread_runs(void)
81{
82 before_thread_runs_arch();
83#ifdef CONFIG_FPU_LAZY
84 if(THREAD==CPU->fpu_owner)
85 fpu_enable();
86 else
87 fpu_disable();
88#else
89 fpu_enable();
90 if (THREAD->fpu_context_exists)
91 fpu_context_restore(THREAD->saved_fpu_context);
92 else {
93 fpu_init();
94 THREAD->fpu_context_exists=1;
95 }
96#endif
97}
98
99/** Take actions after THREAD had run.
100 *
101 * Perform actions that need to be
102 * taken after the running thread
103 * had been preempted by the scheduler.
104 *
105 * THREAD->lock is locked on entry
106 *
107 */
108void after_thread_ran(void)
109{
110 after_thread_ran_arch();
111}
112
113#ifdef CONFIG_FPU_LAZY
114void scheduler_fpu_lazy_request(void)
115{
116restart:
117 fpu_enable();
118 spinlock_lock(&CPU->lock);
119
120 /* Save old context */
121 if (CPU->fpu_owner != NULL) {
122 spinlock_lock(&CPU->fpu_owner->lock);
123 fpu_context_save(CPU->fpu_owner->saved_fpu_context);
124 /* don't prevent migration */
125 CPU->fpu_owner->fpu_context_engaged=0;
126 spinlock_unlock(&CPU->fpu_owner->lock);
127 CPU->fpu_owner = NULL;
128 }
129
130 spinlock_lock(&THREAD->lock);
131 if (THREAD->fpu_context_exists) {
132 fpu_context_restore(THREAD->saved_fpu_context);
133 } else {
134 /* Allocate FPU context */
135 if (!THREAD->saved_fpu_context) {
136 /* Might sleep */
137 spinlock_unlock(&THREAD->lock);
138 spinlock_unlock(&CPU->lock);
139 THREAD->saved_fpu_context = slab_alloc(fpu_context_slab,
140 0);
141 /* We may have switched CPUs during slab_alloc */
142 goto restart;
143 }
144 fpu_init();
145 THREAD->fpu_context_exists=1;
146 }
147 CPU->fpu_owner=THREAD;
148 THREAD->fpu_context_engaged = 1;
149 spinlock_unlock(&THREAD->lock);
150
151 spinlock_unlock(&CPU->lock);
152}
153#endif
154
155/** Initialize scheduler
156 *
157 * Initialize kernel scheduler.
158 *
159 */
160void scheduler_init(void)
161{
162}
163
164/** Get thread to be scheduled
165 *
166 * Get the optimal thread to be scheduled
167 * according to thread accounting and scheduler
168 * policy.
169 *
170 * @return Thread to be scheduled.
171 *
172 */
173static thread_t *find_best_thread(void)
174{
175 thread_t *t;
176 runq_t *r;
177 int i;
178
179 ASSERT(CPU != NULL);
180
181loop:
182 interrupts_enable();
183
184 if (atomic_get(&CPU->nrdy) == 0) {
185 /*
186 * For there was nothing to run, the CPU goes to sleep
187 * until a hardware interrupt or an IPI comes.
188 * This improves energy saving and hyperthreading.
189 */
190
191 /*
192 * An interrupt might occur right now and wake up a thread.
193 * In such case, the CPU will continue to go to sleep
194 * even though there is a runnable thread.
195 */
196
197 cpu_sleep();
198 goto loop;
199 }
200
201 interrupts_disable();
202
203 for (i = 0; i<RQ_COUNT; i++) {
204 r = &CPU->rq[i];
205 spinlock_lock(&r->lock);
206 if (r->n == 0) {
207 /*
208 * If this queue is empty, try a lower-priority queue.
209 */
210 spinlock_unlock(&r->lock);
211 continue;
212 }
213
214 atomic_dec(&CPU->nrdy);
215 atomic_dec(&nrdy);
216 r->n--;
217
218 /*
219 * Take the first thread from the queue.
220 */
221 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
222 list_remove(&t->rq_link);
223
224 spinlock_unlock(&r->lock);
225
226 spinlock_lock(&t->lock);
227 t->cpu = CPU;
228
229 t->ticks = us2ticks((i+1)*10000);
230 t->priority = i; /* correct rq index */
231
232 /*
233 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
234 */
235 t->flags &= ~X_STOLEN;
236 spinlock_unlock(&t->lock);
237
238 return t;
239 }
240 goto loop;
241
242}
243
244/** Prevent rq starvation
245 *
246 * Prevent low priority threads from starving in rq's.
247 *
248 * When the function decides to relink rq's, it reconnects
249 * respective pointers so that in result threads with 'pri'
250 * greater or equal @start are moved to a higher-priority queue.
251 *
252 * @param start Threshold priority.
253 *
254 */
255static void relink_rq(int start)
256{
257 link_t head;
258 runq_t *r;
259 int i, n;
260
261 list_initialize(&head);
262 spinlock_lock(&CPU->lock);
263 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
264 for (i = start; i<RQ_COUNT-1; i++) {
265 /* remember and empty rq[i + 1] */
266 r = &CPU->rq[i + 1];
267 spinlock_lock(&r->lock);
268 list_concat(&head, &r->rq_head);
269 n = r->n;
270 r->n = 0;
271 spinlock_unlock(&r->lock);
272
273 /* append rq[i + 1] to rq[i] */
274 r = &CPU->rq[i];
275 spinlock_lock(&r->lock);
276 list_concat(&r->rq_head, &head);
277 r->n += n;
278 spinlock_unlock(&r->lock);
279 }
280 CPU->needs_relink = 0;
281 }
282 spinlock_unlock(&CPU->lock);
283
284}
285
286/** The scheduler
287 *
288 * The thread scheduling procedure.
289 * Passes control directly to
290 * scheduler_separated_stack().
291 *
292 */
293void scheduler(void)
294{
295 volatile ipl_t ipl;
296
297 ASSERT(CPU != NULL);
298
299 ipl = interrupts_disable();
300
301 if (atomic_get(&haltstate))
302 halt();
303
304 if (THREAD) {
305 spinlock_lock(&THREAD->lock);
306#ifndef CONFIG_FPU_LAZY
307 fpu_context_save(THREAD->saved_fpu_context);
308#endif
309 if (!context_save(&THREAD->saved_context)) {
310 /*
311 * This is the place where threads leave scheduler();
312 */
313 spinlock_unlock(&THREAD->lock);
314 interrupts_restore(THREAD->saved_context.ipl);
315
316 return;
317 }
318
319 /*
320 * Interrupt priority level of preempted thread is recorded here
321 * to facilitate scheduler() invocations from interrupts_disable()'d
322 * code (e.g. waitq_sleep_timeout()).
323 */
324 THREAD->saved_context.ipl = ipl;
325 }
326
327 /*
328 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
329 * and preemption counter. At this point THE could be coming either
330 * from THREAD's or CPU's stack.
331 */
332 the_copy(THE, (the_t *) CPU->stack);
333
334 /*
335 * We may not keep the old stack.
336 * Reason: If we kept the old stack and got blocked, for instance, in
337 * find_best_thread(), the old thread could get rescheduled by another
338 * CPU and overwrite the part of its own stack that was also used by
339 * the scheduler on this CPU.
340 *
341 * Moreover, we have to bypass the compiler-generated POP sequence
342 * which is fooled by SP being set to the very top of the stack.
343 * Therefore the scheduler() function continues in
344 * scheduler_separated_stack().
345 */
346 context_save(&CPU->saved_context);
347 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), (__address) CPU->stack, CPU_STACK_SIZE);
348 context_restore(&CPU->saved_context);
349 /* not reached */
350}
351
352/** Scheduler stack switch wrapper
353 *
354 * Second part of the scheduler() function
355 * using new stack. Handling the actual context
356 * switch to a new thread.
357 *
358 * Assume THREAD->lock is held.
359 */
360void scheduler_separated_stack(void)
361{
362 int priority;
363
364 ASSERT(CPU != NULL);
365
366 if (THREAD) {
367 /* must be run after the switch to scheduler stack */
368 after_thread_ran();
369
370 switch (THREAD->state) {
371 case Running:
372 spinlock_unlock(&THREAD->lock);
373 thread_ready(THREAD);
374 break;
375
376 case Exiting:
377 thread_destroy(THREAD);
378 break;
379
380 case Sleeping:
381 /*
382 * Prefer the thread after it's woken up.
383 */
384 THREAD->priority = -1;
385
386 /*
387 * We need to release wq->lock which we locked in waitq_sleep().
388 * Address of wq->lock is kept in THREAD->sleep_queue.
389 */
390 spinlock_unlock(&THREAD->sleep_queue->lock);
391
392 /*
393 * Check for possible requests for out-of-context invocation.
394 */
395 if (THREAD->call_me) {
396 THREAD->call_me(THREAD->call_me_with);
397 THREAD->call_me = NULL;
398 THREAD->call_me_with = NULL;
399 }
400
401 spinlock_unlock(&THREAD->lock);
402
403 break;
404
405 default:
406 /*
407 * Entering state is unexpected.
408 */
409 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
410 break;
411 }
412
413 THREAD = NULL;
414 }
415
416 THREAD = find_best_thread();
417
418 spinlock_lock(&THREAD->lock);
419 priority = THREAD->priority;
420 spinlock_unlock(&THREAD->lock);
421
422 relink_rq(priority);
423
424 spinlock_lock(&THREAD->lock);
425
426 /*
427 * If both the old and the new task are the same, lots of work is avoided.
428 */
429 if (TASK != THREAD->task) {
430 as_t *as1 = NULL;
431 as_t *as2;
432
433 if (TASK) {
434 spinlock_lock(&TASK->lock);
435 as1 = TASK->as;
436 spinlock_unlock(&TASK->lock);
437 }
438
439 spinlock_lock(&THREAD->task->lock);
440 as2 = THREAD->task->as;
441 spinlock_unlock(&THREAD->task->lock);
442
443 /*
444 * Note that it is possible for two tasks to share one address space.
445 */
446 if (as1 != as2) {
447 /*
448 * Both tasks and address spaces are different.
449 * Replace the old one with the new one.
450 */
451 as_switch(as1, as2);
452 }
453 TASK = THREAD->task;
454 before_task_runs();
455 }
456
457 THREAD->state = Running;
458
459#ifdef SCHEDULER_VERBOSE
460 printf("cpu%d: tid %d (priority=%d,ticks=%lld,nrdy=%ld)\n", CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks, atomic_get(&CPU->nrdy));
461#endif
462
463 /*
464 * Some architectures provide late kernel PA2KA(identity)
465 * mapping in a page fault handler. However, the page fault
466 * handler uses the kernel stack of the running thread and
467 * therefore cannot be used to map it. The kernel stack, if
468 * necessary, is to be mapped in before_thread_runs(). This
469 * function must be executed before the switch to the new stack.
470 */
471 before_thread_runs();
472
473 /*
474 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
475 */
476 the_copy(THE, (the_t *) THREAD->kstack);
477
478 context_restore(&THREAD->saved_context);
479 /* not reached */
480}
481
482#ifdef CONFIG_SMP
483/** Load balancing thread
484 *
485 * SMP load balancing thread, supervising thread supplies
486 * for the CPU it's wired to.
487 *
488 * @param arg Generic thread argument (unused).
489 *
490 */
491void kcpulb(void *arg)
492{
493 thread_t *t;
494 int count, average, i, j, k = 0;
495 ipl_t ipl;
496
497loop:
498 /*
499 * Work in 1s intervals.
500 */
501 thread_sleep(1);
502
503not_satisfied:
504 /*
505 * Calculate the number of threads that will be migrated/stolen from
506 * other CPU's. Note that situation can have changed between two
507 * passes. Each time get the most up to date counts.
508 */
509 average = atomic_get(&nrdy) / config.cpu_active + 1;
510 count = average - atomic_get(&CPU->nrdy);
511
512 if (count <= 0)
513 goto satisfied;
514
515 /*
516 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
517 */
518 for (j=RQ_COUNT-1; j >= 0; j--) {
519 for (i=0; i < config.cpu_active; i++) {
520 link_t *l;
521 runq_t *r;
522 cpu_t *cpu;
523
524 cpu = &cpus[(i + k) % config.cpu_active];
525
526 /*
527 * Not interested in ourselves.
528 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
529 */
530 if (CPU == cpu)
531 continue;
532 if (atomic_get(&cpu->nrdy) <= average)
533 continue;
534
535 ipl = interrupts_disable();
536 r = &cpu->rq[j];
537 spinlock_lock(&r->lock);
538 if (r->n == 0) {
539 spinlock_unlock(&r->lock);
540 interrupts_restore(ipl);
541 continue;
542 }
543
544 t = NULL;
545 l = r->rq_head.prev; /* search rq from the back */
546 while (l != &r->rq_head) {
547 t = list_get_instance(l, thread_t, rq_link);
548 /*
549 * We don't want to steal CPU-wired threads neither threads already stolen.
550 * The latter prevents threads from migrating between CPU's without ever being run.
551 * We don't want to steal threads whose FPU context is still in CPU.
552 */
553 spinlock_lock(&t->lock);
554 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
555 /*
556 * Remove t from r.
557 */
558 spinlock_unlock(&t->lock);
559
560 atomic_dec(&cpu->nrdy);
561 atomic_dec(&nrdy);
562
563 r->n--;
564 list_remove(&t->rq_link);
565
566 break;
567 }
568 spinlock_unlock(&t->lock);
569 l = l->prev;
570 t = NULL;
571 }
572 spinlock_unlock(&r->lock);
573
574 if (t) {
575 /*
576 * Ready t on local CPU
577 */
578 spinlock_lock(&t->lock);
579#ifdef KCPULB_VERBOSE
580 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%ld, avg=%nd\n", CPU->id, t->tid, CPU->id, atomic_get(&CPU->nrdy), atomic_get(&nrdy) / config.cpu_active);
581#endif
582 t->flags |= X_STOLEN;
583 t->state = Entering;
584 spinlock_unlock(&t->lock);
585
586 thread_ready(t);
587
588 interrupts_restore(ipl);
589
590 if (--count == 0)
591 goto satisfied;
592
593 /*
594 * We are not satisfied yet, focus on another CPU next time.
595 */
596 k++;
597
598 continue;
599 }
600 interrupts_restore(ipl);
601 }
602 }
603
604 if (atomic_get(&CPU->nrdy)) {
605 /*
606 * Be a little bit light-weight and let migrated threads run.
607 */
608 scheduler();
609 } else {
610 /*
611 * We failed to migrate a single thread.
612 * Give up this turn.
613 */
614 goto loop;
615 }
616
617 goto not_satisfied;
618
619satisfied:
620 goto loop;
621}
622
623#endif /* CONFIG_SMP */
624
625
626/** Print information about threads & scheduler queues */
627void sched_print_list(void)
628{
629 ipl_t ipl;
630 int cpu,i;
631 runq_t *r;
632 thread_t *t;
633 link_t *cur;
634
635 /* We are going to mess with scheduler structures,
636 * let's not be interrupted */
637 ipl = interrupts_disable();
638 for (cpu=0;cpu < config.cpu_count; cpu++) {
639
640 if (!cpus[cpu].active)
641 continue;
642
643 spinlock_lock(&cpus[cpu].lock);
644 printf("cpu%d: address=%p, nrdy=%ld, needs_relink=%ld\n",
645 cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy), cpus[cpu].needs_relink);
646
647 for (i=0; i<RQ_COUNT; i++) {
648 r = &cpus[cpu].rq[i];
649 spinlock_lock(&r->lock);
650 if (!r->n) {
651 spinlock_unlock(&r->lock);
652 continue;
653 }
654 printf("\trq[%d]: ", i);
655 for (cur=r->rq_head.next; cur!=&r->rq_head; cur=cur->next) {
656 t = list_get_instance(cur, thread_t, rq_link);
657 printf("%d(%s) ", t->tid,
658 thread_states[t->state]);
659 }
660 printf("\n");
661 spinlock_unlock(&r->lock);
662 }
663 spinlock_unlock(&cpus[cpu].lock);
664 }
665
666 interrupts_restore(ipl);
667}
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