source: mainline/generic/src/proc/scheduler.c@ fd8af4b

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since fd8af4b was 7f0837c, checked in by Jakub Jermar <jakub@…>, 20 years ago

Remove the outdated TODO file.
Improve doxygen comments here and there.
  • Property mode set to 100644
File size: 15.0 KB
Line 
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#include <proc/scheduler.h>
30#include <proc/thread.h>
31#include <proc/task.h>
32#include <mm/frame.h>
33#include <mm/page.h>
34#include <mm/as.h>
35#include <arch/asm.h>
36#include <arch/faddr.h>
37#include <atomic.h>
38#include <synch/spinlock.h>
39#include <config.h>
40#include <context.h>
41#include <func.h>
42#include <arch.h>
43#include <adt/list.h>
44#include <panic.h>
45#include <typedefs.h>
46#include <cpu.h>
47#include <print.h>
48#include <debug.h>
49
50static void before_task_runs(void);
51static void before_thread_runs(void);
52static void after_thread_ran(void);
53static void scheduler_separated_stack(void);
54
55atomic_t nrdy; /**< Number of ready threads in the system. */
56
57/** Carry out actions before new task runs. */
58void before_task_runs(void)
59{
60 before_task_runs_arch();
61}
62
63/** Take actions before new thread runs.
64 *
65 * Perform actions that need to be
66 * taken before the newly selected
67 * tread is passed control.
68 *
69 * THREAD->lock is locked on entry
70 *
71 */
72void before_thread_runs(void)
73{
74 before_thread_runs_arch();
75#ifdef CONFIG_FPU_LAZY
76 if(THREAD==CPU->fpu_owner)
77 fpu_enable();
78 else
79 fpu_disable();
80#else
81 fpu_enable();
82 if (THREAD->fpu_context_exists)
83 fpu_context_restore(THREAD->saved_fpu_context);
84 else {
85 fpu_init();
86 THREAD->fpu_context_exists=1;
87 }
88#endif
89}
90
91/** Take actions after THREAD had run.
92 *
93 * Perform actions that need to be
94 * taken after the running thread
95 * had been preempted by the scheduler.
96 *
97 * THREAD->lock is locked on entry
98 *
99 */
100void after_thread_ran(void)
101{
102 after_thread_ran_arch();
103}
104
105#ifdef CONFIG_FPU_LAZY
106void scheduler_fpu_lazy_request(void)
107{
108restart:
109 fpu_enable();
110 spinlock_lock(&CPU->lock);
111
112 /* Save old context */
113 if (CPU->fpu_owner != NULL) {
114 spinlock_lock(&CPU->fpu_owner->lock);
115 fpu_context_save(CPU->fpu_owner->saved_fpu_context);
116 /* don't prevent migration */
117 CPU->fpu_owner->fpu_context_engaged=0;
118 spinlock_unlock(&CPU->fpu_owner->lock);
119 CPU->fpu_owner = NULL;
120 }
121
122 spinlock_lock(&THREAD->lock);
123 if (THREAD->fpu_context_exists) {
124 fpu_context_restore(THREAD->saved_fpu_context);
125 } else {
126 /* Allocate FPU context */
127 if (!THREAD->saved_fpu_context) {
128 /* Might sleep */
129 spinlock_unlock(&THREAD->lock);
130 spinlock_unlock(&CPU->lock);
131 THREAD->saved_fpu_context = slab_alloc(fpu_context_slab,
132 0);
133 /* We may have switched CPUs during slab_alloc */
134 goto restart;
135 }
136 fpu_init();
137 THREAD->fpu_context_exists=1;
138 }
139 CPU->fpu_owner=THREAD;
140 THREAD->fpu_context_engaged = 1;
141 spinlock_unlock(&THREAD->lock);
142
143 spinlock_unlock(&CPU->lock);
144}
145#endif
146
147/** Initialize scheduler
148 *
149 * Initialize kernel scheduler.
150 *
151 */
152void scheduler_init(void)
153{
154}
155
156/** Get thread to be scheduled
157 *
158 * Get the optimal thread to be scheduled
159 * according to thread accounting and scheduler
160 * policy.
161 *
162 * @return Thread to be scheduled.
163 *
164 */
165static thread_t *find_best_thread(void)
166{
167 thread_t *t;
168 runq_t *r;
169 int i;
170
171 ASSERT(CPU != NULL);
172
173loop:
174 interrupts_enable();
175
176 if (atomic_get(&CPU->nrdy) == 0) {
177 /*
178 * For there was nothing to run, the CPU goes to sleep
179 * until a hardware interrupt or an IPI comes.
180 * This improves energy saving and hyperthreading.
181 */
182
183 /*
184 * An interrupt might occur right now and wake up a thread.
185 * In such case, the CPU will continue to go to sleep
186 * even though there is a runnable thread.
187 */
188
189 cpu_sleep();
190 goto loop;
191 }
192
193 interrupts_disable();
194
195 for (i = 0; i<RQ_COUNT; i++) {
196 r = &CPU->rq[i];
197 spinlock_lock(&r->lock);
198 if (r->n == 0) {
199 /*
200 * If this queue is empty, try a lower-priority queue.
201 */
202 spinlock_unlock(&r->lock);
203 continue;
204 }
205
206 atomic_dec(&CPU->nrdy);
207 atomic_dec(&nrdy);
208 r->n--;
209
210 /*
211 * Take the first thread from the queue.
212 */
213 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
214 list_remove(&t->rq_link);
215
216 spinlock_unlock(&r->lock);
217
218 spinlock_lock(&t->lock);
219 t->cpu = CPU;
220
221 t->ticks = us2ticks((i+1)*10000);
222 t->priority = i; /* correct rq index */
223
224 /*
225 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
226 */
227 t->flags &= ~X_STOLEN;
228 spinlock_unlock(&t->lock);
229
230 return t;
231 }
232 goto loop;
233
234}
235
236/** Prevent rq starvation
237 *
238 * Prevent low priority threads from starving in rq's.
239 *
240 * When the function decides to relink rq's, it reconnects
241 * respective pointers so that in result threads with 'pri'
242 * greater or equal @start are moved to a higher-priority queue.
243 *
244 * @param start Threshold priority.
245 *
246 */
247static void relink_rq(int start)
248{
249 link_t head;
250 runq_t *r;
251 int i, n;
252
253 list_initialize(&head);
254 spinlock_lock(&CPU->lock);
255 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
256 for (i = start; i<RQ_COUNT-1; i++) {
257 /* remember and empty rq[i + 1] */
258 r = &CPU->rq[i + 1];
259 spinlock_lock(&r->lock);
260 list_concat(&head, &r->rq_head);
261 n = r->n;
262 r->n = 0;
263 spinlock_unlock(&r->lock);
264
265 /* append rq[i + 1] to rq[i] */
266 r = &CPU->rq[i];
267 spinlock_lock(&r->lock);
268 list_concat(&r->rq_head, &head);
269 r->n += n;
270 spinlock_unlock(&r->lock);
271 }
272 CPU->needs_relink = 0;
273 }
274 spinlock_unlock(&CPU->lock);
275
276}
277
278/** The scheduler
279 *
280 * The thread scheduling procedure.
281 * Passes control directly to
282 * scheduler_separated_stack().
283 *
284 */
285void scheduler(void)
286{
287 volatile ipl_t ipl;
288
289 ASSERT(CPU != NULL);
290
291 ipl = interrupts_disable();
292
293 if (atomic_get(&haltstate))
294 halt();
295
296 if (THREAD) {
297 spinlock_lock(&THREAD->lock);
298#ifndef CONFIG_FPU_LAZY
299 fpu_context_save(THREAD->saved_fpu_context);
300#endif
301 if (!context_save(&THREAD->saved_context)) {
302 /*
303 * This is the place where threads leave scheduler();
304 */
305 spinlock_unlock(&THREAD->lock);
306 interrupts_restore(THREAD->saved_context.ipl);
307
308 return;
309 }
310
311 /*
312 * Interrupt priority level of preempted thread is recorded here
313 * to facilitate scheduler() invocations from interrupts_disable()'d
314 * code (e.g. waitq_sleep_timeout()).
315 */
316 THREAD->saved_context.ipl = ipl;
317 }
318
319 /*
320 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
321 * and preemption counter. At this point THE could be coming either
322 * from THREAD's or CPU's stack.
323 */
324 the_copy(THE, (the_t *) CPU->stack);
325
326 /*
327 * We may not keep the old stack.
328 * Reason: If we kept the old stack and got blocked, for instance, in
329 * find_best_thread(), the old thread could get rescheduled by another
330 * CPU and overwrite the part of its own stack that was also used by
331 * the scheduler on this CPU.
332 *
333 * Moreover, we have to bypass the compiler-generated POP sequence
334 * which is fooled by SP being set to the very top of the stack.
335 * Therefore the scheduler() function continues in
336 * scheduler_separated_stack().
337 */
338 context_save(&CPU->saved_context);
339 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), (__address) CPU->stack, CPU_STACK_SIZE);
340 context_restore(&CPU->saved_context);
341 /* not reached */
342}
343
344/** Scheduler stack switch wrapper
345 *
346 * Second part of the scheduler() function
347 * using new stack. Handling the actual context
348 * switch to a new thread.
349 *
350 * Assume THREAD->lock is held.
351 */
352void scheduler_separated_stack(void)
353{
354 int priority;
355
356 ASSERT(CPU != NULL);
357
358 if (THREAD) {
359 /* must be run after the switch to scheduler stack */
360 after_thread_ran();
361
362 switch (THREAD->state) {
363 case Running:
364 spinlock_unlock(&THREAD->lock);
365 thread_ready(THREAD);
366 break;
367
368 case Exiting:
369 thread_destroy(THREAD);
370 break;
371
372 case Sleeping:
373 /*
374 * Prefer the thread after it's woken up.
375 */
376 THREAD->priority = -1;
377
378 /*
379 * We need to release wq->lock which we locked in waitq_sleep().
380 * Address of wq->lock is kept in THREAD->sleep_queue.
381 */
382 spinlock_unlock(&THREAD->sleep_queue->lock);
383
384 /*
385 * Check for possible requests for out-of-context invocation.
386 */
387 if (THREAD->call_me) {
388 THREAD->call_me(THREAD->call_me_with);
389 THREAD->call_me = NULL;
390 THREAD->call_me_with = NULL;
391 }
392
393 spinlock_unlock(&THREAD->lock);
394
395 break;
396
397 default:
398 /*
399 * Entering state is unexpected.
400 */
401 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
402 break;
403 }
404
405 THREAD = NULL;
406 }
407
408 THREAD = find_best_thread();
409
410 spinlock_lock(&THREAD->lock);
411 priority = THREAD->priority;
412 spinlock_unlock(&THREAD->lock);
413
414 relink_rq(priority);
415
416 spinlock_lock(&THREAD->lock);
417
418 /*
419 * If both the old and the new task are the same, lots of work is avoided.
420 */
421 if (TASK != THREAD->task) {
422 as_t *as1 = NULL;
423 as_t *as2;
424
425 if (TASK) {
426 spinlock_lock(&TASK->lock);
427 as1 = TASK->as;
428 spinlock_unlock(&TASK->lock);
429 }
430
431 spinlock_lock(&THREAD->task->lock);
432 as2 = THREAD->task->as;
433 spinlock_unlock(&THREAD->task->lock);
434
435 /*
436 * Note that it is possible for two tasks to share one address space.
437 */
438 if (as1 != as2) {
439 /*
440 * Both tasks and address spaces are different.
441 * Replace the old one with the new one.
442 */
443 as_switch(as1, as2);
444 }
445 TASK = THREAD->task;
446 before_task_runs();
447 }
448
449 THREAD->state = Running;
450
451#ifdef SCHEDULER_VERBOSE
452 printf("cpu%d: tid %d (priority=%d,ticks=%lld,nrdy=%ld)\n", CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks, atomic_get(&CPU->nrdy));
453#endif
454
455 /*
456 * Some architectures provide late kernel PA2KA(identity)
457 * mapping in a page fault handler. However, the page fault
458 * handler uses the kernel stack of the running thread and
459 * therefore cannot be used to map it. The kernel stack, if
460 * necessary, is to be mapped in before_thread_runs(). This
461 * function must be executed before the switch to the new stack.
462 */
463 before_thread_runs();
464
465 /*
466 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
467 */
468 the_copy(THE, (the_t *) THREAD->kstack);
469
470 context_restore(&THREAD->saved_context);
471 /* not reached */
472}
473
474#ifdef CONFIG_SMP
475/** Load balancing thread
476 *
477 * SMP load balancing thread, supervising thread supplies
478 * for the CPU it's wired to.
479 *
480 * @param arg Generic thread argument (unused).
481 *
482 */
483void kcpulb(void *arg)
484{
485 thread_t *t;
486 int count, average, i, j, k = 0;
487 ipl_t ipl;
488
489loop:
490 /*
491 * Work in 1s intervals.
492 */
493 thread_sleep(1);
494
495not_satisfied:
496 /*
497 * Calculate the number of threads that will be migrated/stolen from
498 * other CPU's. Note that situation can have changed between two
499 * passes. Each time get the most up to date counts.
500 */
501 average = atomic_get(&nrdy) / config.cpu_active + 1;
502 count = average - atomic_get(&CPU->nrdy);
503
504 if (count <= 0)
505 goto satisfied;
506
507 /*
508 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
509 */
510 for (j=RQ_COUNT-1; j >= 0; j--) {
511 for (i=0; i < config.cpu_active; i++) {
512 link_t *l;
513 runq_t *r;
514 cpu_t *cpu;
515
516 cpu = &cpus[(i + k) % config.cpu_active];
517
518 /*
519 * Not interested in ourselves.
520 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
521 */
522 if (CPU == cpu)
523 continue;
524 if (atomic_get(&cpu->nrdy) <= average)
525 continue;
526
527 ipl = interrupts_disable();
528 r = &cpu->rq[j];
529 spinlock_lock(&r->lock);
530 if (r->n == 0) {
531 spinlock_unlock(&r->lock);
532 interrupts_restore(ipl);
533 continue;
534 }
535
536 t = NULL;
537 l = r->rq_head.prev; /* search rq from the back */
538 while (l != &r->rq_head) {
539 t = list_get_instance(l, thread_t, rq_link);
540 /*
541 * We don't want to steal CPU-wired threads neither threads already stolen.
542 * The latter prevents threads from migrating between CPU's without ever being run.
543 * We don't want to steal threads whose FPU context is still in CPU.
544 */
545 spinlock_lock(&t->lock);
546 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
547 /*
548 * Remove t from r.
549 */
550 spinlock_unlock(&t->lock);
551
552 atomic_dec(&cpu->nrdy);
553 atomic_dec(&nrdy);
554
555 r->n--;
556 list_remove(&t->rq_link);
557
558 break;
559 }
560 spinlock_unlock(&t->lock);
561 l = l->prev;
562 t = NULL;
563 }
564 spinlock_unlock(&r->lock);
565
566 if (t) {
567 /*
568 * Ready t on local CPU
569 */
570 spinlock_lock(&t->lock);
571#ifdef KCPULB_VERBOSE
572 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);
573#endif
574 t->flags |= X_STOLEN;
575 t->state = Entering;
576 spinlock_unlock(&t->lock);
577
578 thread_ready(t);
579
580 interrupts_restore(ipl);
581
582 if (--count == 0)
583 goto satisfied;
584
585 /*
586 * We are not satisfied yet, focus on another CPU next time.
587 */
588 k++;
589
590 continue;
591 }
592 interrupts_restore(ipl);
593 }
594 }
595
596 if (atomic_get(&CPU->nrdy)) {
597 /*
598 * Be a little bit light-weight and let migrated threads run.
599 */
600 scheduler();
601 } else {
602 /*
603 * We failed to migrate a single thread.
604 * Give up this turn.
605 */
606 goto loop;
607 }
608
609 goto not_satisfied;
610
611satisfied:
612 goto loop;
613}
614
615#endif /* CONFIG_SMP */
616
617
618/** Print information about threads & scheduler queues */
619void sched_print_list(void)
620{
621 ipl_t ipl;
622 int cpu,i;
623 runq_t *r;
624 thread_t *t;
625 link_t *cur;
626
627 /* We are going to mess with scheduler structures,
628 * let's not be interrupted */
629 ipl = interrupts_disable();
630 for (cpu=0;cpu < config.cpu_count; cpu++) {
631
632 if (!cpus[cpu].active)
633 continue;
634
635 spinlock_lock(&cpus[cpu].lock);
636 printf("cpu%d: address=%p, nrdy=%ld, needs_relink=%ld\n",
637 cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy), cpus[cpu].needs_relink);
638
639 for (i=0; i<RQ_COUNT; i++) {
640 r = &cpus[cpu].rq[i];
641 spinlock_lock(&r->lock);
642 if (!r->n) {
643 spinlock_unlock(&r->lock);
644 continue;
645 }
646 printf("\trq[%d]: ", i);
647 for (cur=r->rq_head.next; cur!=&r->rq_head; cur=cur->next) {
648 t = list_get_instance(cur, thread_t, rq_link);
649 printf("%d(%s) ", t->tid,
650 thread_states[t->state]);
651 }
652 printf("\n");
653 spinlock_unlock(&r->lock);
654 }
655 spinlock_unlock(&cpus[cpu].lock);
656 }
657
658 interrupts_restore(ipl);
659}
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