source: mainline/src/proc/scheduler.c@ c5ae095

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since c5ae095 was ba18512, checked in by Jakub Jermar <jakub@…>, 20 years ago

Switch order of 'src' and 'dst' arguments in some left-over uses of memcopy.

Cleanup.
  • Property mode set to 100644
File size: 12.8 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
50
51volatile int 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
93loop:
94 cpu_priority_high();
95
96 spinlock_lock(&CPU->lock);
97 n = CPU->nrdy;
98 spinlock_unlock(&CPU->lock);
99
100 cpu_priority_low();
101
102 if (n == 0) {
103 #ifdef __SMP__
104 /*
105 * If the load balancing thread is not running, wake it up and
106 * set CPU-private flag that the kcpulb has been started.
107 */
108 if (test_and_set(&CPU->kcpulbstarted) == 0) {
109 waitq_wakeup(&CPU->kcpulb_wq, 0);
110 goto loop;
111 }
112 #endif /* __SMP__ */
113
114 /*
115 * For there was nothing to run, the CPU goes to sleep
116 * until a hardware interrupt or an IPI comes.
117 * This improves energy saving and hyperthreading.
118 * On the other hand, several hardware interrupts can be ignored.
119 */
120 cpu_sleep();
121 goto loop;
122 }
123
124 cpu_priority_high();
125
126 i = 0;
127retry:
128 for (; i<RQ_COUNT; i++) {
129 r = &CPU->rq[i];
130 spinlock_lock(&r->lock);
131 if (r->n == 0) {
132 /*
133 * If this queue is empty, try a lower-priority queue.
134 */
135 spinlock_unlock(&r->lock);
136 continue;
137 }
138
139 /* avoid deadlock with relink_rq() */
140 if (!spinlock_trylock(&CPU->lock)) {
141 /*
142 * Unlock r and try again.
143 */
144 spinlock_unlock(&r->lock);
145 goto retry;
146 }
147 CPU->nrdy--;
148 spinlock_unlock(&CPU->lock);
149
150 atomic_dec(&nrdy);
151 r->n--;
152
153 /*
154 * Take the first thread from the queue.
155 */
156 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
157 list_remove(&t->rq_link);
158
159 spinlock_unlock(&r->lock);
160
161 spinlock_lock(&t->lock);
162 t->cpu = CPU;
163
164 t->ticks = us2ticks((i+1)*10000);
165 t->pri = i; /* eventually correct rq index */
166
167 /*
168 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
169 */
170 t->flags &= ~X_STOLEN;
171 spinlock_unlock(&t->lock);
172
173 return t;
174 }
175 goto loop;
176
177}
178
179
180/** Prevent rq starvation
181 *
182 * Prevent low priority threads from starving in rq's.
183 *
184 * When the function decides to relink rq's, it reconnects
185 * respective pointers so that in result threads with 'pri'
186 * greater or equal 'start' are moved to a higher-priority queue.
187 *
188 * @param start Threshold priority.
189 *
190 */
191void relink_rq(int start)
192{
193 link_t head;
194 runq_t *r;
195 int i, n;
196
197 list_initialize(&head);
198 spinlock_lock(&CPU->lock);
199 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
200 for (i = start; i<RQ_COUNT-1; i++) {
201 /* remember and empty rq[i + 1] */
202 r = &CPU->rq[i + 1];
203 spinlock_lock(&r->lock);
204 list_concat(&head, &r->rq_head);
205 n = r->n;
206 r->n = 0;
207 spinlock_unlock(&r->lock);
208
209 /* append rq[i + 1] to rq[i] */
210 r = &CPU->rq[i];
211 spinlock_lock(&r->lock);
212 list_concat(&r->rq_head, &head);
213 r->n += n;
214 spinlock_unlock(&r->lock);
215 }
216 CPU->needs_relink = 0;
217 }
218 spinlock_unlock(&CPU->lock);
219
220}
221
222
223/** The scheduler
224 *
225 * The thread scheduling procedure.
226 *
227 */
228void scheduler(void)
229{
230 volatile pri_t pri;
231
232 pri = cpu_priority_high();
233
234 if (haltstate)
235 halt();
236
237 if (THREAD) {
238 spinlock_lock(&THREAD->lock);
239 fpu_context_save(&(THREAD->saved_fpu_context));
240 if (!context_save(&THREAD->saved_context)) {
241 /*
242 * This is the place where threads leave scheduler();
243 */
244 before_thread_runs();
245 spinlock_unlock(&THREAD->lock);
246 cpu_priority_restore(THREAD->saved_context.pri);
247 return;
248 }
249
250 /*
251 * CPU priority of preempted thread is recorded here
252 * to facilitate scheduler() invocations from
253 * cpu_priority_high()'ed code (e.g. waitq_sleep_timeout()).
254 */
255 THREAD->saved_context.pri = pri;
256 }
257
258 /*
259 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU
260 * and preemption counter. At this point THE could be coming either
261 * from THREAD's or CPU's stack.
262 */
263 the_copy(THE, (the_t *) CPU->stack);
264
265 /*
266 * We may not keep the old stack.
267 * Reason: If we kept the old stack and got blocked, for instance, in
268 * find_best_thread(), the old thread could get rescheduled by another
269 * CPU and overwrite the part of its own stack that was also used by
270 * the scheduler on this CPU.
271 *
272 * Moreover, we have to bypass the compiler-generated POP sequence
273 * which is fooled by SP being set to the very top of the stack.
274 * Therefore the scheduler() function continues in
275 * scheduler_separated_stack().
276 */
277 context_save(&CPU->saved_context);
278 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
279 context_restore(&CPU->saved_context);
280 /* not reached */
281}
282
283
284/** Scheduler stack switch wrapper
285 *
286 * Second part of the scheduler() function
287 * using new stack. Handling the actual context
288 * switch to a new thread.
289 *
290 */
291void scheduler_separated_stack(void)
292{
293 int priority;
294
295 if (THREAD) {
296 switch (THREAD->state) {
297 case Running:
298 THREAD->state = Ready;
299 spinlock_unlock(&THREAD->lock);
300 thread_ready(THREAD);
301 break;
302
303 case Exiting:
304 frame_free((__address) THREAD->kstack);
305 if (THREAD->ustack) {
306 frame_free((__address) THREAD->ustack);
307 }
308
309 /*
310 * Detach from the containing task.
311 */
312 spinlock_lock(&TASK->lock);
313 list_remove(&THREAD->th_link);
314 spinlock_unlock(&TASK->lock);
315
316 spinlock_unlock(&THREAD->lock);
317
318 spinlock_lock(&threads_lock);
319 list_remove(&THREAD->threads_link);
320 spinlock_unlock(&threads_lock);
321
322 spinlock_lock(&CPU->lock);
323 if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
324 spinlock_unlock(&CPU->lock);
325
326 free(THREAD);
327
328 break;
329
330 case Sleeping:
331 /*
332 * Prefer the thread after it's woken up.
333 */
334 THREAD->pri = -1;
335
336 /*
337 * We need to release wq->lock which we locked in waitq_sleep().
338 * Address of wq->lock is kept in THREAD->sleep_queue.
339 */
340 spinlock_unlock(&THREAD->sleep_queue->lock);
341
342 /*
343 * Check for possible requests for out-of-context invocation.
344 */
345 if (THREAD->call_me) {
346 THREAD->call_me(THREAD->call_me_with);
347 THREAD->call_me = NULL;
348 THREAD->call_me_with = NULL;
349 }
350
351 spinlock_unlock(&THREAD->lock);
352
353 break;
354
355 default:
356 /*
357 * Entering state is unexpected.
358 */
359 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
360 break;
361 }
362 THREAD = NULL;
363 }
364
365 THREAD = find_best_thread();
366
367 spinlock_lock(&THREAD->lock);
368 priority = THREAD->pri;
369 spinlock_unlock(&THREAD->lock);
370
371 relink_rq(priority);
372
373 spinlock_lock(&THREAD->lock);
374
375 /*
376 * If both the old and the new task are the same, lots of work is avoided.
377 */
378 if (TASK != THREAD->task) {
379 vm_t *m1 = NULL;
380 vm_t *m2;
381
382 if (TASK) {
383 spinlock_lock(&TASK->lock);
384 m1 = TASK->vm;
385 spinlock_unlock(&TASK->lock);
386 }
387
388 spinlock_lock(&THREAD->task->lock);
389 m2 = THREAD->task->vm;
390 spinlock_unlock(&THREAD->task->lock);
391
392 /*
393 * Note that it is possible for two tasks to share one vm mapping.
394 */
395 if (m1 != m2) {
396 /*
397 * Both tasks and vm mappings are different.
398 * Replace the old one with the new one.
399 */
400 vm_install(m2);
401 }
402 TASK = THREAD->task;
403 }
404
405 THREAD->state = Running;
406
407 #ifdef SCHEDULER_VERBOSE
408 printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
409 #endif
410
411 the_copy(THE, (the_t *) THREAD->kstack);
412
413 context_restore(&THREAD->saved_context);
414 /* not reached */
415}
416
417
418#ifdef __SMP__
419/** Load balancing thread
420 *
421 * SMP load balancing thread, supervising thread supplies
422 * for the CPU it's wired to.
423 *
424 * @param arg Generic thread argument (unused).
425 *
426 */
427void kcpulb(void *arg)
428{
429 thread_t *t;
430 int count, i, j, k = 0;
431 pri_t pri;
432
433loop:
434 /*
435 * Sleep until there's some work to do.
436 */
437 waitq_sleep(&CPU->kcpulb_wq);
438
439not_satisfied:
440 /*
441 * Calculate the number of threads that will be migrated/stolen from
442 * other CPU's. Note that situation can have changed between two
443 * passes. Each time get the most up to date counts.
444 */
445 pri = cpu_priority_high();
446 spinlock_lock(&CPU->lock);
447 count = nrdy / config.cpu_active;
448 count -= CPU->nrdy;
449 spinlock_unlock(&CPU->lock);
450 cpu_priority_restore(pri);
451
452 if (count <= 0)
453 goto satisfied;
454
455 /*
456 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
457 */
458 for (j=RQ_COUNT-1; j >= 0; j--) {
459 for (i=0; i < config.cpu_active; i++) {
460 link_t *l;
461 runq_t *r;
462 cpu_t *cpu;
463
464 cpu = &cpus[(i + k) % config.cpu_active];
465
466 /*
467 * Not interested in ourselves.
468 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
469 */
470 if (CPU == cpu)
471 continue;
472
473restart: pri = cpu_priority_high();
474 r = &cpu->rq[j];
475 spinlock_lock(&r->lock);
476 if (r->n == 0) {
477 spinlock_unlock(&r->lock);
478 cpu_priority_restore(pri);
479 continue;
480 }
481
482 t = NULL;
483 l = r->rq_head.prev; /* search rq from the back */
484 while (l != &r->rq_head) {
485 t = list_get_instance(l, thread_t, rq_link);
486 /*
487 * We don't want to steal CPU-wired threads neither threads already stolen.
488 * The latter prevents threads from migrating between CPU's without ever being run.
489 * We don't want to steal threads whose FPU context is still in CPU.
490 */
491 spinlock_lock(&t->lock);
492 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
493
494 /*
495 * Remove t from r.
496 */
497
498 spinlock_unlock(&t->lock);
499
500 /*
501 * Here we have to avoid deadlock with relink_rq(),
502 * because it locks cpu and r in a different order than we do.
503 */
504 if (!spinlock_trylock(&cpu->lock)) {
505 /* Release all locks and try again. */
506 spinlock_unlock(&r->lock);
507 cpu_priority_restore(pri);
508 goto restart;
509 }
510 cpu->nrdy--;
511 spinlock_unlock(&cpu->lock);
512
513 atomic_dec(&nrdy);
514
515 r->n--;
516 list_remove(&t->rq_link);
517
518 break;
519 }
520 spinlock_unlock(&t->lock);
521 l = l->prev;
522 t = NULL;
523 }
524 spinlock_unlock(&r->lock);
525
526 if (t) {
527 /*
528 * Ready t on local CPU
529 */
530 spinlock_lock(&t->lock);
531 #ifdef KCPULB_VERBOSE
532 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
533 #endif
534 t->flags |= X_STOLEN;
535 spinlock_unlock(&t->lock);
536
537 thread_ready(t);
538
539 cpu_priority_restore(pri);
540
541 if (--count == 0)
542 goto satisfied;
543
544 /*
545 * We are not satisfied yet, focus on another CPU next time.
546 */
547 k++;
548
549 continue;
550 }
551 cpu_priority_restore(pri);
552 }
553 }
554
555 if (CPU->nrdy) {
556 /*
557 * Be a little bit light-weight and let migrated threads run.
558 */
559 scheduler();
560 }
561 else {
562 /*
563 * We failed to migrate a single thread.
564 * Something more sophisticated should be done.
565 */
566 scheduler();
567 }
568
569 goto not_satisfied;
570
571satisfied:
572 /*
573 * Tell find_best_thread() to wake us up later again.
574 */
575 CPU->kcpulbstarted = 0;
576 goto loop;
577}
578
579#endif /* __SMP__ */
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