source: mainline/src/proc/scheduler.c@ 4b2c872d

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 4b2c872d was 4b2c872d, checked in by Jakub Jermar <jakub@…>, 20 years ago

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