source: mainline/generic/src/proc/scheduler.c@ 36a140b

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 36a140b was 5f85c91, checked in by Martin Decky <martin@…>, 20 years ago

make configuration variables usage consistent
  • 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 CONFIG_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 CONFIG_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 */
119static struct 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 CONFIG_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 /* CONFIG_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 */
225static void 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/** Scheduler stack switch wrapper
258 *
259 * Second part of the scheduler() function
260 * using new stack. Handling the actual context
261 * switch to a new thread.
262 *
263 */
264static void scheduler_separated_stack(void)
265{
266 int priority;
267
268 ASSERT(CPU != NULL);
269
270 if (THREAD) {
271 switch (THREAD->state) {
272 case Running:
273 THREAD->state = Ready;
274 spinlock_unlock(&THREAD->lock);
275 thread_ready(THREAD);
276 break;
277
278 case Exiting:
279 frame_free((__address) THREAD->kstack);
280 if (THREAD->ustack) {
281 frame_free((__address) THREAD->ustack);
282 }
283
284 /*
285 * Detach from the containing task.
286 */
287 spinlock_lock(&TASK->lock);
288 list_remove(&THREAD->th_link);
289 spinlock_unlock(&TASK->lock);
290
291 spinlock_unlock(&THREAD->lock);
292
293 spinlock_lock(&threads_lock);
294 list_remove(&THREAD->threads_link);
295 spinlock_unlock(&threads_lock);
296
297 spinlock_lock(&CPU->lock);
298 if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
299 spinlock_unlock(&CPU->lock);
300
301 free(THREAD);
302
303 break;
304
305 case Sleeping:
306 /*
307 * Prefer the thread after it's woken up.
308 */
309 THREAD->priority = -1;
310
311 /*
312 * We need to release wq->lock which we locked in waitq_sleep().
313 * Address of wq->lock is kept in THREAD->sleep_queue.
314 */
315 spinlock_unlock(&THREAD->sleep_queue->lock);
316
317 /*
318 * Check for possible requests for out-of-context invocation.
319 */
320 if (THREAD->call_me) {
321 THREAD->call_me(THREAD->call_me_with);
322 THREAD->call_me = NULL;
323 THREAD->call_me_with = NULL;
324 }
325
326 spinlock_unlock(&THREAD->lock);
327
328 break;
329
330 default:
331 /*
332 * Entering state is unexpected.
333 */
334 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
335 break;
336 }
337 THREAD = NULL;
338 }
339
340
341 THREAD = find_best_thread();
342
343 spinlock_lock(&THREAD->lock);
344 priority = THREAD->priority;
345 spinlock_unlock(&THREAD->lock);
346
347 relink_rq(priority);
348
349 spinlock_lock(&THREAD->lock);
350
351 /*
352 * If both the old and the new task are the same, lots of work is avoided.
353 */
354 if (TASK != THREAD->task) {
355 vm_t *m1 = NULL;
356 vm_t *m2;
357
358 if (TASK) {
359 spinlock_lock(&TASK->lock);
360 m1 = TASK->vm;
361 spinlock_unlock(&TASK->lock);
362 }
363
364 spinlock_lock(&THREAD->task->lock);
365 m2 = THREAD->task->vm;
366 spinlock_unlock(&THREAD->task->lock);
367
368 /*
369 * Note that it is possible for two tasks to share one vm mapping.
370 */
371 if (m1 != m2) {
372 /*
373 * Both tasks and vm mappings are different.
374 * Replace the old one with the new one.
375 */
376 vm_install(m2);
377 }
378 TASK = THREAD->task;
379 }
380
381 THREAD->state = Running;
382
383 #ifdef SCHEDULER_VERBOSE
384 printf("cpu%d: tid %d (priority=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks, CPU->nrdy);
385 #endif
386
387 /*
388 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
389 */
390 the_copy(THE, (the_t *) THREAD->kstack);
391
392 context_restore(&THREAD->saved_context);
393 /* not reached */
394}
395
396
397/** The scheduler
398 *
399 * The thread scheduling procedure.
400 *
401 */
402void scheduler(void)
403{
404 volatile ipl_t ipl;
405
406 ASSERT(CPU != NULL);
407
408 ipl = interrupts_disable();
409
410 if (haltstate)
411 halt();
412
413 if (THREAD) {
414 spinlock_lock(&THREAD->lock);
415#ifndef CONFIG_FPU_LAZY
416 fpu_context_save(&(THREAD->saved_fpu_context));
417#endif
418 if (!context_save(&THREAD->saved_context)) {
419 /*
420 * This is the place where threads leave scheduler();
421 */
422 before_thread_runs();
423 spinlock_unlock(&THREAD->lock);
424 interrupts_restore(THREAD->saved_context.ipl);
425 return;
426 }
427
428 /*
429 * Interrupt priority level of preempted thread is recorded here
430 * to facilitate scheduler() invocations from interrupts_disable()'d
431 * code (e.g. waitq_sleep_timeout()).
432 */
433 THREAD->saved_context.ipl = ipl;
434 }
435
436 /*
437 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU
438 * and preemption counter. At this point THE could be coming either
439 * from THREAD's or CPU's stack.
440 */
441 the_copy(THE, (the_t *) CPU->stack);
442
443 /*
444 * We may not keep the old stack.
445 * Reason: If we kept the old stack and got blocked, for instance, in
446 * find_best_thread(), the old thread could get rescheduled by another
447 * CPU and overwrite the part of its own stack that was also used by
448 * the scheduler on this CPU.
449 *
450 * Moreover, we have to bypass the compiler-generated POP sequence
451 * which is fooled by SP being set to the very top of the stack.
452 * Therefore the scheduler() function continues in
453 * scheduler_separated_stack().
454 */
455 context_save(&CPU->saved_context);
456 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), (__address) CPU->stack, CPU_STACK_SIZE);
457 context_restore(&CPU->saved_context);
458 /* not reached */
459}
460
461
462
463
464
465#ifdef CONFIG_SMP
466/** Load balancing thread
467 *
468 * SMP load balancing thread, supervising thread supplies
469 * for the CPU it's wired to.
470 *
471 * @param arg Generic thread argument (unused).
472 *
473 */
474void kcpulb(void *arg)
475{
476 thread_t *t;
477 int count, i, j, k = 0;
478 ipl_t ipl;
479
480loop:
481 /*
482 * Sleep until there's some work to do.
483 */
484 waitq_sleep(&CPU->kcpulb_wq);
485
486not_satisfied:
487 /*
488 * Calculate the number of threads that will be migrated/stolen from
489 * other CPU's. Note that situation can have changed between two
490 * passes. Each time get the most up to date counts.
491 */
492 ipl = interrupts_disable();
493 spinlock_lock(&CPU->lock);
494 count = nrdy / config.cpu_active;
495 count -= CPU->nrdy;
496 spinlock_unlock(&CPU->lock);
497 interrupts_restore(ipl);
498
499 if (count <= 0)
500 goto satisfied;
501
502 /*
503 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
504 */
505 for (j=RQ_COUNT-1; j >= 0; j--) {
506 for (i=0; i < config.cpu_active; i++) {
507 link_t *l;
508 runq_t *r;
509 cpu_t *cpu;
510
511 cpu = &cpus[(i + k) % config.cpu_active];
512
513 /*
514 * Not interested in ourselves.
515 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
516 */
517 if (CPU == cpu)
518 continue;
519
520restart: ipl = interrupts_disable();
521 r = &cpu->rq[j];
522 spinlock_lock(&r->lock);
523 if (r->n == 0) {
524 spinlock_unlock(&r->lock);
525 interrupts_restore(ipl);
526 continue;
527 }
528
529 t = NULL;
530 l = r->rq_head.prev; /* search rq from the back */
531 while (l != &r->rq_head) {
532 t = list_get_instance(l, thread_t, rq_link);
533 /*
534 * We don't want to steal CPU-wired threads neither threads already stolen.
535 * The latter prevents threads from migrating between CPU's without ever being run.
536 * We don't want to steal threads whose FPU context is still in CPU.
537 */
538 spinlock_lock(&t->lock);
539 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
540
541 /*
542 * Remove t from r.
543 */
544
545 spinlock_unlock(&t->lock);
546
547 /*
548 * Here we have to avoid deadlock with relink_rq(),
549 * because it locks cpu and r in a different order than we do.
550 */
551 if (!spinlock_trylock(&cpu->lock)) {
552 /* Release all locks and try again. */
553 spinlock_unlock(&r->lock);
554 interrupts_restore(ipl);
555 goto restart;
556 }
557 cpu->nrdy--;
558 spinlock_unlock(&cpu->lock);
559
560 atomic_dec((int *)&nrdy);
561
562 r->n--;
563 list_remove(&t->rq_link);
564
565 break;
566 }
567 spinlock_unlock(&t->lock);
568 l = l->prev;
569 t = NULL;
570 }
571 spinlock_unlock(&r->lock);
572
573 if (t) {
574 /*
575 * Ready t on local CPU
576 */
577 spinlock_lock(&t->lock);
578 #ifdef KCPULB_VERBOSE
579 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
580 #endif
581 t->flags |= X_STOLEN;
582 spinlock_unlock(&t->lock);
583
584 thread_ready(t);
585
586 interrupts_restore(ipl);
587
588 if (--count == 0)
589 goto satisfied;
590
591 /*
592 * We are not satisfied yet, focus on another CPU next time.
593 */
594 k++;
595
596 continue;
597 }
598 interrupts_restore(ipl);
599 }
600 }
601
602 if (CPU->nrdy) {
603 /*
604 * Be a little bit light-weight and let migrated threads run.
605 */
606 scheduler();
607 }
608 else {
609 /*
610 * We failed to migrate a single thread.
611 * Something more sophisticated should be done.
612 */
613 scheduler();
614 }
615
616 goto not_satisfied;
617
618satisfied:
619 /*
620 * Tell find_best_thread() to wake us up later again.
621 */
622 CPU->kcpulbstarted = 0;
623 goto loop;
624}
625
626#endif /* CONFIG_SMP */
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