source: mainline/src/proc/scheduler.c@ 18e0a6c

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since 18e0a6c was 18e0a6c, checked in by Jakub Jermar <jakub@…>, 20 years ago

Implement several assembler functions in gcc's asm notation instead of in .s or .S file.
Gain both better speed and size.
  • Property mode set to 100644
File size: 12.6 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
47volatile int nrdy;
48
49
50/** Initialize context switching
51 *
52 * Initialize context switching and lazy FPU
53 * context switching.
54 *
55 */
56void before_thread_runs(void)
57{
58 before_thread_runs_arch();
59 fpu_context_restore(&(THREAD->saved_fpu_context));
60}
61
62
63/** Initialize scheduler
64 *
65 * Initialize kernel scheduler.
66 *
67 */
68void scheduler_init(void)
69{
70}
71
72
73/** Get thread to be scheduled
74 *
75 * Get the optimal thread to be scheduled
76 * according to thread accounting and scheduler
77 * policy.
78 *
79 * @return Thread to be scheduled.
80 *
81 */
82struct thread *find_best_thread(void)
83{
84 thread_t *t;
85 runq_t *r;
86 int i, n;
87
88loop:
89 cpu_priority_high();
90
91 spinlock_lock(&CPU->lock);
92 n = CPU->nrdy;
93 spinlock_unlock(&CPU->lock);
94
95 cpu_priority_low();
96
97 if (n == 0) {
98 #ifdef __SMP__
99 /*
100 * If the load balancing thread is not running, wake it up and
101 * set CPU-private flag that the kcpulb has been started.
102 */
103 if (test_and_set(&CPU->kcpulbstarted) == 0) {
104 waitq_wakeup(&CPU->kcpulb_wq, 0);
105 goto loop;
106 }
107 #endif /* __SMP__ */
108
109 /*
110 * For there was nothing to run, the CPU goes to sleep
111 * until a hardware interrupt or an IPI comes.
112 * This improves energy saving and hyperthreading.
113 * On the other hand, several hardware interrupts can be ignored.
114 */
115 cpu_sleep();
116 goto loop;
117 }
118
119 cpu_priority_high();
120
121 i = 0;
122retry:
123 for (; i<RQ_COUNT; i++) {
124 r = &CPU->rq[i];
125 spinlock_lock(&r->lock);
126 if (r->n == 0) {
127 /*
128 * If this queue is empty, try a lower-priority queue.
129 */
130 spinlock_unlock(&r->lock);
131 continue;
132 }
133
134 /* avoid deadlock with relink_rq() */
135 if (!spinlock_trylock(&CPU->lock)) {
136 /*
137 * Unlock r and try again.
138 */
139 spinlock_unlock(&r->lock);
140 goto retry;
141 }
142 CPU->nrdy--;
143 spinlock_unlock(&CPU->lock);
144
145 atomic_dec(&nrdy);
146 r->n--;
147
148 /*
149 * Take the first thread from the queue.
150 */
151 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
152 list_remove(&t->rq_link);
153
154 spinlock_unlock(&r->lock);
155
156 spinlock_lock(&t->lock);
157 t->cpu = CPU;
158
159 t->ticks = us2ticks((i+1)*10000);
160 t->pri = i; /* eventually correct rq index */
161
162 /*
163 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
164 */
165 t->flags &= ~X_STOLEN;
166 spinlock_unlock(&t->lock);
167
168 return t;
169 }
170 goto loop;
171
172}
173
174
175/** Prevent rq starvation
176 *
177 * Prevent low priority threads from starving in rq's.
178 *
179 * When the function decides to relink rq's, it reconnects
180 * respective pointers so that in result threads with 'pri'
181 * greater or equal 'start' are moved to a higher-priority queue.
182 *
183 * @param start Threshold priority.
184 *
185 */
186void relink_rq(int start)
187{
188 link_t head;
189 runq_t *r;
190 int i, n;
191
192 list_initialize(&head);
193 spinlock_lock(&CPU->lock);
194 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
195 for (i = start; i<RQ_COUNT-1; i++) {
196 /* remember and empty rq[i + 1] */
197 r = &CPU->rq[i + 1];
198 spinlock_lock(&r->lock);
199 list_concat(&head, &r->rq_head);
200 n = r->n;
201 r->n = 0;
202 spinlock_unlock(&r->lock);
203
204 /* append rq[i + 1] to rq[i] */
205 r = &CPU->rq[i];
206 spinlock_lock(&r->lock);
207 list_concat(&r->rq_head, &head);
208 r->n += n;
209 spinlock_unlock(&r->lock);
210 }
211 CPU->needs_relink = 0;
212 }
213 spinlock_unlock(&CPU->lock);
214
215}
216
217
218/** The scheduler
219 *
220 * The thread scheduling procedure.
221 *
222 */
223void scheduler(void)
224{
225 volatile pri_t pri;
226
227 pri = cpu_priority_high();
228
229 if (haltstate)
230 halt();
231
232 if (THREAD) {
233 spinlock_lock(&THREAD->lock);
234 fpu_context_save(&(THREAD->saved_fpu_context));
235 if (!context_save(&THREAD->saved_context)) {
236 /*
237 * This is the place where threads leave scheduler();
238 */
239 before_thread_runs();
240 spinlock_unlock(&THREAD->lock);
241 cpu_priority_restore(THREAD->saved_context.pri);
242 return;
243 }
244 THREAD->saved_context.pri = pri;
245 }
246
247 /*
248 * We may not keep the old stack.
249 * Reason: If we kept the old stack and got blocked, for instance, in
250 * find_best_thread(), the old thread could get rescheduled by another
251 * CPU and overwrite the part of its own stack that was also used by
252 * the scheduler on this CPU.
253 *
254 * Moreover, we have to bypass the compiler-generated POP sequence
255 * which is fooled by SP being set to the very top of the stack.
256 * Therefore the scheduler() function continues in
257 * scheduler_separated_stack().
258 */
259 context_save(&CPU->saved_context);
260 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
261 context_restore(&CPU->saved_context);
262 /* not reached */
263}
264
265
266/** Scheduler stack switch wrapper
267 *
268 * Second part of the scheduler() function
269 * using new stack. Handling the actual context
270 * switch to a new thread.
271 *
272 */
273void scheduler_separated_stack(void)
274{
275 int priority;
276
277 if (THREAD) {
278 switch (THREAD->state) {
279 case Running:
280 THREAD->state = Ready;
281 spinlock_unlock(&THREAD->lock);
282 thread_ready(THREAD);
283 break;
284
285 case Exiting:
286 frame_free((__address) THREAD->kstack);
287 if (THREAD->ustack) {
288 frame_free((__address) THREAD->ustack);
289 }
290
291 /*
292 * Detach from the containing task.
293 */
294 spinlock_lock(&TASK->lock);
295 list_remove(&THREAD->th_link);
296 spinlock_unlock(&TASK->lock);
297
298 spinlock_unlock(&THREAD->lock);
299
300 spinlock_lock(&threads_lock);
301 list_remove(&THREAD->threads_link);
302 spinlock_unlock(&threads_lock);
303
304 spinlock_lock(&CPU->lock);
305 if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
306 spinlock_unlock(&CPU->lock);
307
308
309 free(THREAD);
310
311 break;
312
313 case Sleeping:
314 /*
315 * Prefer the thread after it's woken up.
316 */
317 THREAD->pri = -1;
318
319 /*
320 * We need to release wq->lock which we locked in waitq_sleep().
321 * Address of wq->lock is kept in THREAD->sleep_queue.
322 */
323 spinlock_unlock(&THREAD->sleep_queue->lock);
324
325 /*
326 * Check for possible requests for out-of-context invocation.
327 */
328 if (THREAD->call_me) {
329 THREAD->call_me(THREAD->call_me_with);
330 THREAD->call_me = NULL;
331 THREAD->call_me_with = NULL;
332 }
333
334 spinlock_unlock(&THREAD->lock);
335
336 break;
337
338 default:
339 /*
340 * Entering state is unexpected.
341 */
342 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
343 break;
344 }
345 THREAD = NULL;
346 }
347
348 THREAD = find_best_thread();
349
350 spinlock_lock(&THREAD->lock);
351 priority = THREAD->pri;
352 spinlock_unlock(&THREAD->lock);
353
354 relink_rq(priority);
355
356 spinlock_lock(&THREAD->lock);
357
358 /*
359 * If both the old and the new task are the same, lots of work is avoided.
360 */
361 if (TASK != THREAD->task) {
362 vm_t *m1 = NULL;
363 vm_t *m2;
364
365 if (TASK) {
366 spinlock_lock(&TASK->lock);
367 m1 = TASK->vm;
368 spinlock_unlock(&TASK->lock);
369 }
370
371 spinlock_lock(&THREAD->task->lock);
372 m2 = THREAD->task->vm;
373 spinlock_unlock(&THREAD->task->lock);
374
375 /*
376 * Note that it is possible for two tasks to share one vm mapping.
377 */
378 if (m1 != m2) {
379 /*
380 * Both tasks and vm mappings are different.
381 * Replace the old one with the new one.
382 */
383 if (m1) {
384 vm_uninstall(m1);
385 }
386 vm_install(m2);
387 }
388 TASK = THREAD->task;
389 }
390
391 THREAD->state = Running;
392
393 #ifdef SCHEDULER_VERBOSE
394 printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
395 #endif
396
397 context_restore(&THREAD->saved_context);
398 /* not reached */
399}
400
401
402#ifdef __SMP__
403/** Load balancing thread
404 *
405 * SMP load balancing thread, supervising thread supplies
406 * for the CPU it's wired to.
407 *
408 * @param arg Generic thread argument (unused).
409 *
410 */
411void kcpulb(void *arg)
412{
413 thread_t *t;
414 int count, i, j, k = 0;
415 pri_t pri;
416
417loop:
418 /*
419 * Sleep until there's some work to do.
420 */
421 waitq_sleep(&CPU->kcpulb_wq);
422
423not_satisfied:
424 /*
425 * Calculate the number of threads that will be migrated/stolen from
426 * other CPU's. Note that situation can have changed between two
427 * passes. Each time get the most up to date counts.
428 */
429 pri = cpu_priority_high();
430 spinlock_lock(&CPU->lock);
431 count = nrdy / config.cpu_active;
432 count -= CPU->nrdy;
433 spinlock_unlock(&CPU->lock);
434 cpu_priority_restore(pri);
435
436 if (count <= 0)
437 goto satisfied;
438
439 /*
440 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
441 */
442 for (j=RQ_COUNT-1; j >= 0; j--) {
443 for (i=0; i < config.cpu_active; i++) {
444 link_t *l;
445 runq_t *r;
446 cpu_t *cpu;
447
448 cpu = &cpus[(i + k) % config.cpu_active];
449
450 /*
451 * Not interested in ourselves.
452 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
453 */
454 if (CPU == cpu)
455 continue;
456
457restart: pri = cpu_priority_high();
458 r = &cpu->rq[j];
459 spinlock_lock(&r->lock);
460 if (r->n == 0) {
461 spinlock_unlock(&r->lock);
462 cpu_priority_restore(pri);
463 continue;
464 }
465
466 t = NULL;
467 l = r->rq_head.prev; /* search rq from the back */
468 while (l != &r->rq_head) {
469 t = list_get_instance(l, thread_t, rq_link);
470 /*
471 * We don't want to steal CPU-wired threads neither threads already stolen.
472 * The latter prevents threads from migrating between CPU's without ever being run.
473 * We don't want to steal threads whose FPU context is still in CPU.
474 */
475 spinlock_lock(&t->lock);
476 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
477
478 /*
479 * Remove t from r.
480 */
481
482 spinlock_unlock(&t->lock);
483
484 /*
485 * Here we have to avoid deadlock with relink_rq(),
486 * because it locks cpu and r in a different order than we do.
487 */
488 if (!spinlock_trylock(&cpu->lock)) {
489 /* Release all locks and try again. */
490 spinlock_unlock(&r->lock);
491 cpu_priority_restore(pri);
492 goto restart;
493 }
494 cpu->nrdy--;
495 spinlock_unlock(&cpu->lock);
496
497 atomic_dec(&nrdy);
498
499 r->n--;
500 list_remove(&t->rq_link);
501
502 break;
503 }
504 spinlock_unlock(&t->lock);
505 l = l->prev;
506 t = NULL;
507 }
508 spinlock_unlock(&r->lock);
509
510 if (t) {
511 /*
512 * Ready t on local CPU
513 */
514 spinlock_lock(&t->lock);
515 #ifdef KCPULB_VERBOSE
516 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
517 #endif
518 t->flags |= X_STOLEN;
519 spinlock_unlock(&t->lock);
520
521 thread_ready(t);
522
523 cpu_priority_restore(pri);
524
525 if (--count == 0)
526 goto satisfied;
527
528 /*
529 * We are not satisfied yet, focus on another CPU next time.
530 */
531 k++;
532
533 continue;
534 }
535 cpu_priority_restore(pri);
536 }
537 }
538
539 if (CPU->nrdy) {
540 /*
541 * Be a little bit light-weight and let migrated threads run.
542 */
543 scheduler();
544 }
545 else {
546 /*
547 * We failed to migrate a single thread.
548 * Something more sophisticated should be done.
549 */
550 scheduler();
551 }
552
553 goto not_satisfied;
554
555satisfied:
556 /*
557 * Tell find_best_thread() to wake us up later again.
558 */
559 CPU->kcpulbstarted = 0;
560 goto loop;
561}
562
563#endif /* __SMP__ */
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