source: mainline/src/proc/scheduler.c@ 7df54df

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 7df54df was 73838ed, checked in by Ondrej Palkovsky <ondrap@…>, 20 years ago

Cleanups so that it compiles on ia-32 & amd-64 cleanly
  • Property mode set to 100644
File size: 13.0 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 <cpu.h>
33#include <mm/vm.h>
34#include <config.h>
35#include <context.h>
36#include <func.h>
37#include <arch.h>
38#include <arch/asm.h>
39#include <list.h>
40#include <panic.h>
41#include <typedefs.h>
42#include <mm/page.h>
43#include <synch/spinlock.h>
44#include <arch/faddr.h>
45#include <arch/atomic.h>
46#include <print.h>
47#include <mm/frame.h>
48#include <mm/heap.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 fpu_context_restore(&(THREAD->saved_fpu_context));
65}
66
67
68/** Initialize scheduler
69 *
70 * Initialize kernel scheduler.
71 *
72 */
73void scheduler_init(void)
74{
75}
76
77
78/** Get thread to be scheduled
79 *
80 * Get the optimal thread to be scheduled
81 * according to thread accounting and scheduler
82 * policy.
83 *
84 * @return Thread to be scheduled.
85 *
86 */
87struct thread *find_best_thread(void)
88{
89 thread_t *t;
90 runq_t *r;
91 int i, n;
92
93 ASSERT(CPU != NULL);
94
95loop:
96 cpu_priority_high();
97
98 spinlock_lock(&CPU->lock);
99 n = CPU->nrdy;
100 spinlock_unlock(&CPU->lock);
101
102 cpu_priority_low();
103
104 if (n == 0) {
105 #ifdef __SMP__
106 /*
107 * If the load balancing thread is not running, wake it up and
108 * set CPU-private flag that the kcpulb has been started.
109 */
110 if (test_and_set(&CPU->kcpulbstarted) == 0) {
111 waitq_wakeup(&CPU->kcpulb_wq, 0);
112 goto loop;
113 }
114 #endif /* __SMP__ */
115
116 /*
117 * For there was nothing to run, the CPU goes to sleep
118 * until a hardware interrupt or an IPI comes.
119 * This improves energy saving and hyperthreading.
120 * On the other hand, several hardware interrupts can be ignored.
121 */
122 cpu_sleep();
123 goto loop;
124 }
125
126 cpu_priority_high();
127
128 i = 0;
129retry:
130 for (; i<RQ_COUNT; i++) {
131 r = &CPU->rq[i];
132 spinlock_lock(&r->lock);
133 if (r->n == 0) {
134 /*
135 * If this queue is empty, try a lower-priority queue.
136 */
137 spinlock_unlock(&r->lock);
138 continue;
139 }
140
141 /* avoid deadlock with relink_rq() */
142 if (!spinlock_trylock(&CPU->lock)) {
143 /*
144 * Unlock r and try again.
145 */
146 spinlock_unlock(&r->lock);
147 goto retry;
148 }
149 CPU->nrdy--;
150 spinlock_unlock(&CPU->lock);
151
152 atomic_dec(&nrdy);
153 r->n--;
154
155 /*
156 * Take the first thread from the queue.
157 */
158 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
159 list_remove(&t->rq_link);
160
161 spinlock_unlock(&r->lock);
162
163 spinlock_lock(&t->lock);
164 t->cpu = CPU;
165
166 t->ticks = us2ticks((i+1)*10000);
167 t->pri = i; /* eventually correct rq index */
168
169 /*
170 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
171 */
172 t->flags &= ~X_STOLEN;
173 spinlock_unlock(&t->lock);
174
175 return t;
176 }
177 goto loop;
178
179}
180
181
182/** Prevent rq starvation
183 *
184 * Prevent low priority threads from starving in rq's.
185 *
186 * When the function decides to relink rq's, it reconnects
187 * respective pointers so that in result threads with 'pri'
188 * greater or equal 'start' are moved to a higher-priority queue.
189 *
190 * @param start Threshold priority.
191 *
192 */
193void relink_rq(int start)
194{
195 link_t head;
196 runq_t *r;
197 int i, n;
198
199 list_initialize(&head);
200 spinlock_lock(&CPU->lock);
201 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
202 for (i = start; i<RQ_COUNT-1; i++) {
203 /* remember and empty rq[i + 1] */
204 r = &CPU->rq[i + 1];
205 spinlock_lock(&r->lock);
206 list_concat(&head, &r->rq_head);
207 n = r->n;
208 r->n = 0;
209 spinlock_unlock(&r->lock);
210
211 /* append rq[i + 1] to rq[i] */
212 r = &CPU->rq[i];
213 spinlock_lock(&r->lock);
214 list_concat(&r->rq_head, &head);
215 r->n += n;
216 spinlock_unlock(&r->lock);
217 }
218 CPU->needs_relink = 0;
219 }
220 spinlock_unlock(&CPU->lock);
221
222}
223
224
225/** The scheduler
226 *
227 * The thread scheduling procedure.
228 *
229 */
230void scheduler(void)
231{
232 volatile pri_t pri;
233
234 ASSERT(CPU != NULL);
235
236 pri = cpu_priority_high();
237
238 if (haltstate)
239 halt();
240
241 if (THREAD) {
242 spinlock_lock(&THREAD->lock);
243 fpu_context_save(&(THREAD->saved_fpu_context));
244 if (!context_save(&THREAD->saved_context)) {
245 /*
246 * This is the place where threads leave scheduler();
247 */
248 before_thread_runs();
249 spinlock_unlock(&THREAD->lock);
250 cpu_priority_restore(THREAD->saved_context.pri);
251 return;
252 }
253
254 /*
255 * CPU priority of preempted thread is recorded here
256 * to facilitate scheduler() invocations from
257 * cpu_priority_high()'ed code (e.g. waitq_sleep_timeout()).
258 */
259 THREAD->saved_context.pri = pri;
260 }
261
262 /*
263 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU
264 * and preemption counter. At this point THE could be coming either
265 * from THREAD's or CPU's stack.
266 */
267 the_copy(THE, (the_t *) CPU->stack);
268
269 /*
270 * We may not keep the old stack.
271 * Reason: If we kept the old stack and got blocked, for instance, in
272 * find_best_thread(), the old thread could get rescheduled by another
273 * CPU and overwrite the part of its own stack that was also used by
274 * the scheduler on this CPU.
275 *
276 * Moreover, we have to bypass the compiler-generated POP sequence
277 * which is fooled by SP being set to the very top of the stack.
278 * Therefore the scheduler() function continues in
279 * scheduler_separated_stack().
280 */
281 context_save(&CPU->saved_context);
282 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
283 context_restore(&CPU->saved_context);
284 /* not reached */
285}
286
287
288/** Scheduler stack switch wrapper
289 *
290 * Second part of the scheduler() function
291 * using new stack. Handling the actual context
292 * switch to a new thread.
293 *
294 */
295void scheduler_separated_stack(void)
296{
297 int priority;
298
299 ASSERT(CPU != NULL);
300
301 if (THREAD) {
302 switch (THREAD->state) {
303 case Running:
304 THREAD->state = Ready;
305 spinlock_unlock(&THREAD->lock);
306 thread_ready(THREAD);
307 break;
308
309 case Exiting:
310 frame_free((__address) THREAD->kstack);
311 if (THREAD->ustack) {
312 frame_free((__address) THREAD->ustack);
313 }
314
315 /*
316 * Detach from the containing task.
317 */
318 spinlock_lock(&TASK->lock);
319 list_remove(&THREAD->th_link);
320 spinlock_unlock(&TASK->lock);
321
322 spinlock_unlock(&THREAD->lock);
323
324 spinlock_lock(&threads_lock);
325 list_remove(&THREAD->threads_link);
326 spinlock_unlock(&threads_lock);
327
328 spinlock_lock(&CPU->lock);
329 if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
330 spinlock_unlock(&CPU->lock);
331
332 free(THREAD);
333
334 break;
335
336 case Sleeping:
337 /*
338 * Prefer the thread after it's woken up.
339 */
340 THREAD->pri = -1;
341
342 /*
343 * We need to release wq->lock which we locked in waitq_sleep().
344 * Address of wq->lock is kept in THREAD->sleep_queue.
345 */
346 spinlock_unlock(&THREAD->sleep_queue->lock);
347
348 /*
349 * Check for possible requests for out-of-context invocation.
350 */
351 if (THREAD->call_me) {
352 THREAD->call_me(THREAD->call_me_with);
353 THREAD->call_me = NULL;
354 THREAD->call_me_with = NULL;
355 }
356
357 spinlock_unlock(&THREAD->lock);
358
359 break;
360
361 default:
362 /*
363 * Entering state is unexpected.
364 */
365 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
366 break;
367 }
368 THREAD = NULL;
369 }
370
371
372 THREAD = find_best_thread();
373
374 spinlock_lock(&THREAD->lock);
375 priority = THREAD->pri;
376 spinlock_unlock(&THREAD->lock);
377
378 relink_rq(priority);
379
380 spinlock_lock(&THREAD->lock);
381
382 /*
383 * If both the old and the new task are the same, lots of work is avoided.
384 */
385 if (TASK != THREAD->task) {
386 vm_t *m1 = NULL;
387 vm_t *m2;
388
389 if (TASK) {
390 spinlock_lock(&TASK->lock);
391 m1 = TASK->vm;
392 spinlock_unlock(&TASK->lock);
393 }
394
395 spinlock_lock(&THREAD->task->lock);
396 m2 = THREAD->task->vm;
397 spinlock_unlock(&THREAD->task->lock);
398
399 /*
400 * Note that it is possible for two tasks to share one vm mapping.
401 */
402 if (m1 != m2) {
403 /*
404 * Both tasks and vm mappings are different.
405 * Replace the old one with the new one.
406 */
407 vm_install(m2);
408 }
409 TASK = THREAD->task;
410 }
411
412 THREAD->state = Running;
413
414 #ifdef SCHEDULER_VERBOSE
415 printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
416 #endif
417
418 /*
419 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
420 */
421 the_copy(THE, (the_t *) THREAD->kstack);
422
423 context_restore(&THREAD->saved_context);
424 /* not reached */
425}
426
427
428#ifdef __SMP__
429/** Load balancing thread
430 *
431 * SMP load balancing thread, supervising thread supplies
432 * for the CPU it's wired to.
433 *
434 * @param arg Generic thread argument (unused).
435 *
436 */
437void kcpulb(void *arg)
438{
439 thread_t *t;
440 int count, i, j, k = 0;
441 pri_t pri;
442
443loop:
444 /*
445 * Sleep until there's some work to do.
446 */
447 waitq_sleep(&CPU->kcpulb_wq);
448
449not_satisfied:
450 /*
451 * Calculate the number of threads that will be migrated/stolen from
452 * other CPU's. Note that situation can have changed between two
453 * passes. Each time get the most up to date counts.
454 */
455 pri = cpu_priority_high();
456 spinlock_lock(&CPU->lock);
457 count = nrdy / config.cpu_active;
458 count -= CPU->nrdy;
459 spinlock_unlock(&CPU->lock);
460 cpu_priority_restore(pri);
461
462 if (count <= 0)
463 goto satisfied;
464
465 /*
466 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
467 */
468 for (j=RQ_COUNT-1; j >= 0; j--) {
469 for (i=0; i < config.cpu_active; i++) {
470 link_t *l;
471 runq_t *r;
472 cpu_t *cpu;
473
474 cpu = &cpus[(i + k) % config.cpu_active];
475
476 /*
477 * Not interested in ourselves.
478 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
479 */
480 if (CPU == cpu)
481 continue;
482
483restart: pri = cpu_priority_high();
484 r = &cpu->rq[j];
485 spinlock_lock(&r->lock);
486 if (r->n == 0) {
487 spinlock_unlock(&r->lock);
488 cpu_priority_restore(pri);
489 continue;
490 }
491
492 t = NULL;
493 l = r->rq_head.prev; /* search rq from the back */
494 while (l != &r->rq_head) {
495 t = list_get_instance(l, thread_t, rq_link);
496 /*
497 * We don't want to steal CPU-wired threads neither threads already stolen.
498 * The latter prevents threads from migrating between CPU's without ever being run.
499 * We don't want to steal threads whose FPU context is still in CPU.
500 */
501 spinlock_lock(&t->lock);
502 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
503
504 /*
505 * Remove t from r.
506 */
507
508 spinlock_unlock(&t->lock);
509
510 /*
511 * Here we have to avoid deadlock with relink_rq(),
512 * because it locks cpu and r in a different order than we do.
513 */
514 if (!spinlock_trylock(&cpu->lock)) {
515 /* Release all locks and try again. */
516 spinlock_unlock(&r->lock);
517 cpu_priority_restore(pri);
518 goto restart;
519 }
520 cpu->nrdy--;
521 spinlock_unlock(&cpu->lock);
522
523 atomic_dec(&nrdy);
524
525 r->n--;
526 list_remove(&t->rq_link);
527
528 break;
529 }
530 spinlock_unlock(&t->lock);
531 l = l->prev;
532 t = NULL;
533 }
534 spinlock_unlock(&r->lock);
535
536 if (t) {
537 /*
538 * Ready t on local CPU
539 */
540 spinlock_lock(&t->lock);
541 #ifdef KCPULB_VERBOSE
542 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
543 #endif
544 t->flags |= X_STOLEN;
545 spinlock_unlock(&t->lock);
546
547 thread_ready(t);
548
549 cpu_priority_restore(pri);
550
551 if (--count == 0)
552 goto satisfied;
553
554 /*
555 * We are not satisfied yet, focus on another CPU next time.
556 */
557 k++;
558
559 continue;
560 }
561 cpu_priority_restore(pri);
562 }
563 }
564
565 if (CPU->nrdy) {
566 /*
567 * Be a little bit light-weight and let migrated threads run.
568 */
569 scheduler();
570 }
571 else {
572 /*
573 * We failed to migrate a single thread.
574 * Something more sophisticated should be done.
575 */
576 scheduler();
577 }
578
579 goto not_satisfied;
580
581satisfied:
582 /*
583 * Tell find_best_thread() to wake us up later again.
584 */
585 CPU->kcpulbstarted = 0;
586 goto loop;
587}
588
589#endif /* __SMP__ */
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