source: mainline/generic/src/proc/scheduler.c@ 05e2a7ad

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 05e2a7ad was 05e2a7ad, checked in by Jakub Jermar <jakub@…>, 20 years ago

Add comments describing locking rules for some locks.
Cleanup.
  • Property mode set to 100644
File size: 13.7 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/heap.h>
33#include <mm/frame.h>
34#include <mm/page.h>
35#include <mm/vm.h>
36#include <arch/asm.h>
37#include <arch/faddr.h>
38#include <arch/atomic.h>
39#include <synch/spinlock.h>
40#include <config.h>
41#include <context.h>
42#include <func.h>
43#include <arch.h>
44#include <list.h>
45#include <panic.h>
46#include <typedefs.h>
47#include <cpu.h>
48#include <print.h>
49#include <debug.h>
50
51atomic_t nrdy;
52
53/** Take actions before new thread runs
54 *
55 * Perform actions that need to be
56 * taken before the newly selected
57 * tread is passed control.
58 *
59 */
60void before_thread_runs(void)
61{
62 before_thread_runs_arch();
63#ifdef CONFIG_FPU_LAZY
64 if(THREAD==CPU->fpu_owner)
65 fpu_enable();
66 else
67 fpu_disable();
68#else
69 fpu_enable();
70 if (THREAD->fpu_context_exists)
71 fpu_context_restore(&(THREAD->saved_fpu_context));
72 else {
73 fpu_init();
74 THREAD->fpu_context_exists=1;
75 }
76#endif
77}
78
79#ifdef CONFIG_FPU_LAZY
80void scheduler_fpu_lazy_request(void)
81{
82 fpu_enable();
83 if (CPU->fpu_owner != NULL) {
84 fpu_context_save(&CPU->fpu_owner->saved_fpu_context);
85 /* don't prevent migration */
86 CPU->fpu_owner->fpu_context_engaged=0;
87 }
88 if (THREAD->fpu_context_exists)
89 fpu_context_restore(&THREAD->saved_fpu_context);
90 else {
91 fpu_init();
92 THREAD->fpu_context_exists=1;
93 }
94 CPU->fpu_owner=THREAD;
95 THREAD->fpu_context_engaged = 1;
96}
97#endif
98
99/** Initialize scheduler
100 *
101 * Initialize kernel scheduler.
102 *
103 */
104void scheduler_init(void)
105{
106}
107
108
109/** Get thread to be scheduled
110 *
111 * Get the optimal thread to be scheduled
112 * according to thread accounting and scheduler
113 * policy.
114 *
115 * @return Thread to be scheduled.
116 *
117 */
118static thread_t *find_best_thread(void)
119{
120 thread_t *t;
121 runq_t *r;
122 int i, n;
123
124 ASSERT(CPU != NULL);
125
126loop:
127 interrupts_disable();
128
129 spinlock_lock(&CPU->lock);
130 n = CPU->nrdy;
131 spinlock_unlock(&CPU->lock);
132
133 interrupts_enable();
134
135 if (n == 0) {
136 #ifdef CONFIG_SMP
137 /*
138 * If the load balancing thread is not running, wake it up and
139 * set CPU-private flag that the kcpulb has been started.
140 */
141 if (test_and_set(&CPU->kcpulbstarted) == 0) {
142 waitq_wakeup(&CPU->kcpulb_wq, 0);
143 goto loop;
144 }
145 #endif /* CONFIG_SMP */
146
147 /*
148 * For there was nothing to run, the CPU goes to sleep
149 * until a hardware interrupt or an IPI comes.
150 * This improves energy saving and hyperthreading.
151 * On the other hand, several hardware interrupts can be ignored.
152 */
153 cpu_sleep();
154 goto loop;
155 }
156
157 interrupts_disable();
158
159 i = 0;
160retry:
161 for (; i<RQ_COUNT; i++) {
162 r = &CPU->rq[i];
163 spinlock_lock(&r->lock);
164 if (r->n == 0) {
165 /*
166 * If this queue is empty, try a lower-priority queue.
167 */
168 spinlock_unlock(&r->lock);
169 continue;
170 }
171
172 /* avoid deadlock with relink_rq() */
173 if (!spinlock_trylock(&CPU->lock)) {
174 /*
175 * Unlock r and try again.
176 */
177 spinlock_unlock(&r->lock);
178 goto retry;
179 }
180 CPU->nrdy--;
181 spinlock_unlock(&CPU->lock);
182
183 atomic_dec(&nrdy);
184 r->n--;
185
186 /*
187 * Take the first thread from the queue.
188 */
189 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
190 list_remove(&t->rq_link);
191
192 spinlock_unlock(&r->lock);
193
194 spinlock_lock(&t->lock);
195 t->cpu = CPU;
196
197 t->ticks = us2ticks((i+1)*10000);
198 t->priority = i; /* eventually correct rq index */
199
200 /*
201 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
202 */
203 t->flags &= ~X_STOLEN;
204 spinlock_unlock(&t->lock);
205
206 return t;
207 }
208 goto loop;
209
210}
211
212
213/** Prevent rq starvation
214 *
215 * Prevent low priority threads from starving in rq's.
216 *
217 * When the function decides to relink rq's, it reconnects
218 * respective pointers so that in result threads with 'pri'
219 * greater or equal 'start' are moved to a higher-priority queue.
220 *
221 * @param start Threshold priority.
222 *
223 */
224static void relink_rq(int start)
225{
226 link_t head;
227 runq_t *r;
228 int i, n;
229
230 list_initialize(&head);
231 spinlock_lock(&CPU->lock);
232 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
233 for (i = start; i<RQ_COUNT-1; i++) {
234 /* remember and empty rq[i + 1] */
235 r = &CPU->rq[i + 1];
236 spinlock_lock(&r->lock);
237 list_concat(&head, &r->rq_head);
238 n = r->n;
239 r->n = 0;
240 spinlock_unlock(&r->lock);
241
242 /* append rq[i + 1] to rq[i] */
243 r = &CPU->rq[i];
244 spinlock_lock(&r->lock);
245 list_concat(&r->rq_head, &head);
246 r->n += n;
247 spinlock_unlock(&r->lock);
248 }
249 CPU->needs_relink = 0;
250 }
251 spinlock_unlock(&CPU->lock);
252
253}
254
255
256/** Scheduler stack switch wrapper
257 *
258 * Second part of the scheduler() function
259 * using new stack. Handling the actual context
260 * switch to a new thread.
261 *
262 */
263static void scheduler_separated_stack(void)
264{
265 int priority;
266
267 ASSERT(CPU != NULL);
268
269 if (THREAD) {
270 switch (THREAD->state) {
271 case Running:
272 THREAD->state = Ready;
273 spinlock_unlock(&THREAD->lock);
274 thread_ready(THREAD);
275 break;
276
277 case Exiting:
278 frame_free((__address) THREAD->kstack);
279 if (THREAD->ustack) {
280 frame_free((__address) THREAD->ustack);
281 }
282
283 /*
284 * Detach from the containing task.
285 */
286 spinlock_lock(&TASK->lock);
287 list_remove(&THREAD->th_link);
288 spinlock_unlock(&TASK->lock);
289
290 spinlock_unlock(&THREAD->lock);
291
292 spinlock_lock(&threads_lock);
293 list_remove(&THREAD->threads_link);
294 spinlock_unlock(&threads_lock);
295
296 spinlock_lock(&CPU->lock);
297 if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
298 spinlock_unlock(&CPU->lock);
299
300 free(THREAD);
301
302 break;
303
304 case Sleeping:
305 /*
306 * Prefer the thread after it's woken up.
307 */
308 THREAD->priority = -1;
309
310 /*
311 * We need to release wq->lock which we locked in waitq_sleep().
312 * Address of wq->lock is kept in THREAD->sleep_queue.
313 */
314 spinlock_unlock(&THREAD->sleep_queue->lock);
315
316 /*
317 * Check for possible requests for out-of-context invocation.
318 */
319 if (THREAD->call_me) {
320 THREAD->call_me(THREAD->call_me_with);
321 THREAD->call_me = NULL;
322 THREAD->call_me_with = NULL;
323 }
324
325 spinlock_unlock(&THREAD->lock);
326
327 break;
328
329 default:
330 /*
331 * Entering state is unexpected.
332 */
333 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
334 break;
335 }
336 THREAD = NULL;
337 }
338
339
340 THREAD = find_best_thread();
341
342 spinlock_lock(&THREAD->lock);
343 priority = THREAD->priority;
344 spinlock_unlock(&THREAD->lock);
345
346 relink_rq(priority);
347
348 spinlock_lock(&THREAD->lock);
349
350 /*
351 * If both the old and the new task are the same, lots of work is avoided.
352 */
353 if (TASK != THREAD->task) {
354 vm_t *m1 = NULL;
355 vm_t *m2;
356
357 if (TASK) {
358 spinlock_lock(&TASK->lock);
359 m1 = TASK->vm;
360 spinlock_unlock(&TASK->lock);
361 }
362
363 spinlock_lock(&THREAD->task->lock);
364 m2 = THREAD->task->vm;
365 spinlock_unlock(&THREAD->task->lock);
366
367 /*
368 * Note that it is possible for two tasks to share one vm mapping.
369 */
370 if (m1 != m2) {
371 /*
372 * Both tasks and vm mappings are different.
373 * Replace the old one with the new one.
374 */
375 vm_install(m2);
376 }
377 TASK = THREAD->task;
378 }
379
380 THREAD->state = Running;
381
382 #ifdef SCHEDULER_VERBOSE
383 printf("cpu%d: tid %d (priority=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks, CPU->nrdy);
384 #endif
385
386 /*
387 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
388 */
389 the_copy(THE, (the_t *) THREAD->kstack);
390
391 context_restore(&THREAD->saved_context);
392 /* not reached */
393}
394
395
396/** The scheduler
397 *
398 * The thread scheduling procedure.
399 *
400 */
401void scheduler(void)
402{
403 volatile ipl_t ipl;
404
405 ASSERT(CPU != NULL);
406
407 ipl = interrupts_disable();
408
409 if (haltstate)
410 halt();
411
412 if (THREAD) {
413 spinlock_lock(&THREAD->lock);
414#ifndef CONFIG_FPU_LAZY
415 fpu_context_save(&(THREAD->saved_fpu_context));
416#endif
417 if (!context_save(&THREAD->saved_context)) {
418 /*
419 * This is the place where threads leave scheduler();
420 */
421 before_thread_runs();
422 spinlock_unlock(&THREAD->lock);
423 interrupts_restore(THREAD->saved_context.ipl);
424 return;
425 }
426
427 /*
428 * Interrupt priority level of preempted thread is recorded here
429 * to facilitate scheduler() invocations from interrupts_disable()'d
430 * code (e.g. waitq_sleep_timeout()).
431 */
432 THREAD->saved_context.ipl = ipl;
433 }
434
435 /*
436 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
437 * and preemption counter. At this point THE could be coming either
438 * from THREAD's or CPU's stack.
439 */
440 the_copy(THE, (the_t *) CPU->stack);
441
442 /*
443 * We may not keep the old stack.
444 * Reason: If we kept the old stack and got blocked, for instance, in
445 * find_best_thread(), the old thread could get rescheduled by another
446 * CPU and overwrite the part of its own stack that was also used by
447 * the scheduler on this CPU.
448 *
449 * Moreover, we have to bypass the compiler-generated POP sequence
450 * which is fooled by SP being set to the very top of the stack.
451 * Therefore the scheduler() function continues in
452 * scheduler_separated_stack().
453 */
454 context_save(&CPU->saved_context);
455 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), (__address) CPU->stack, CPU_STACK_SIZE);
456 context_restore(&CPU->saved_context);
457 /* not reached */
458}
459
460
461
462
463
464#ifdef CONFIG_SMP
465/** Load balancing thread
466 *
467 * SMP load balancing thread, supervising thread supplies
468 * for the CPU it's wired to.
469 *
470 * @param arg Generic thread argument (unused).
471 *
472 */
473void kcpulb(void *arg)
474{
475 thread_t *t;
476 int count, i, j, k = 0;
477 ipl_t ipl;
478
479loop:
480 /*
481 * Sleep until there's some work to do.
482 */
483 waitq_sleep(&CPU->kcpulb_wq);
484
485not_satisfied:
486 /*
487 * Calculate the number of threads that will be migrated/stolen from
488 * other CPU's. Note that situation can have changed between two
489 * passes. Each time get the most up to date counts.
490 */
491 ipl = interrupts_disable();
492 spinlock_lock(&CPU->lock);
493 count = nrdy / config.cpu_active;
494 count -= CPU->nrdy;
495 spinlock_unlock(&CPU->lock);
496 interrupts_restore(ipl);
497
498 if (count <= 0)
499 goto satisfied;
500
501 /*
502 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
503 */
504 for (j=RQ_COUNT-1; j >= 0; j--) {
505 for (i=0; i < config.cpu_active; i++) {
506 link_t *l;
507 runq_t *r;
508 cpu_t *cpu;
509
510 cpu = &cpus[(i + k) % config.cpu_active];
511
512 /*
513 * Not interested in ourselves.
514 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
515 */
516 if (CPU == cpu)
517 continue;
518
519restart: ipl = interrupts_disable();
520 r = &cpu->rq[j];
521 spinlock_lock(&r->lock);
522 if (r->n == 0) {
523 spinlock_unlock(&r->lock);
524 interrupts_restore(ipl);
525 continue;
526 }
527
528 t = NULL;
529 l = r->rq_head.prev; /* search rq from the back */
530 while (l != &r->rq_head) {
531 t = list_get_instance(l, thread_t, rq_link);
532 /*
533 * We don't want to steal CPU-wired threads neither threads already stolen.
534 * The latter prevents threads from migrating between CPU's without ever being run.
535 * We don't want to steal threads whose FPU context is still in CPU.
536 */
537 spinlock_lock(&t->lock);
538 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
539
540 /*
541 * Remove t from r.
542 */
543
544 spinlock_unlock(&t->lock);
545
546 /*
547 * Here we have to avoid deadlock with relink_rq(),
548 * because it locks cpu and r in a different order than we do.
549 */
550 if (!spinlock_trylock(&cpu->lock)) {
551 /* Release all locks and try again. */
552 spinlock_unlock(&r->lock);
553 interrupts_restore(ipl);
554 goto restart;
555 }
556 cpu->nrdy--;
557 spinlock_unlock(&cpu->lock);
558
559 atomic_dec(&nrdy);
560
561 r->n--;
562 list_remove(&t->rq_link);
563
564 break;
565 }
566 spinlock_unlock(&t->lock);
567 l = l->prev;
568 t = NULL;
569 }
570 spinlock_unlock(&r->lock);
571
572 if (t) {
573 /*
574 * Ready t on local CPU
575 */
576 spinlock_lock(&t->lock);
577 #ifdef KCPULB_VERBOSE
578 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
579 #endif
580 t->flags |= X_STOLEN;
581 spinlock_unlock(&t->lock);
582
583 thread_ready(t);
584
585 interrupts_restore(ipl);
586
587 if (--count == 0)
588 goto satisfied;
589
590 /*
591 * We are not satisfied yet, focus on another CPU next time.
592 */
593 k++;
594
595 continue;
596 }
597 interrupts_restore(ipl);
598 }
599 }
600
601 if (CPU->nrdy) {
602 /*
603 * Be a little bit light-weight and let migrated threads run.
604 */
605 scheduler();
606 }
607 else {
608 /*
609 * We failed to migrate a single thread.
610 * Something more sophisticated should be done.
611 */
612 scheduler();
613 }
614
615 goto not_satisfied;
616
617satisfied:
618 /*
619 * Tell find_best_thread() to wake us up later again.
620 */
621 CPU->kcpulbstarted = 0;
622 goto loop;
623}
624
625#endif /* CONFIG_SMP */
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