source: mainline/generic/src/proc/scheduler.c@ f76fed4

lfn serial ticket/834-toolchain-update topic/msim-upgrade topic/simplify-dev-export
Last change on this file since f76fed4 was f76fed4, checked in by Ondrej Palkovsky <ondrap@…>, 19 years ago

Added lazy fpu context allocation.

  • threads that don't use fpu, don't get allocated fpu context
  • fpu context alignment on AMD64 nicely disappeared
  • Property mode set to 100644
File size: 14.7 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/frame.h>
33#include <mm/page.h>
34#include <mm/as.h>
35#include <arch/asm.h>
36#include <arch/faddr.h>
37#include <arch/atomic.h>
38#include <synch/spinlock.h>
39#include <config.h>
40#include <context.h>
41#include <func.h>
42#include <arch.h>
43#include <adt/list.h>
44#include <panic.h>
45#include <typedefs.h>
46#include <cpu.h>
47#include <print.h>
48#include <debug.h>
49
50static void scheduler_separated_stack(void);
51
52atomic_t nrdy; /**< Number of ready threads in the system. */
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 * THREAD->lock is locked on entry
61 *
62 */
63void before_thread_runs(void)
64{
65 before_thread_runs_arch();
66#ifdef CONFIG_FPU_LAZY
67 if(THREAD==CPU->fpu_owner)
68 fpu_enable();
69 else
70 fpu_disable();
71#else
72 fpu_enable();
73 if (THREAD->fpu_context_exists)
74 fpu_context_restore(THREAD->saved_fpu_context);
75 else {
76 fpu_init();
77 THREAD->fpu_context_exists=1;
78 }
79#endif
80}
81
82/** Take actions after THREAD had run.
83 *
84 * Perform actions that need to be
85 * taken after the running thread
86 * had been preempted by the scheduler.
87 *
88 * THREAD->lock is locked on entry
89 *
90 */
91void after_thread_ran(void)
92{
93 after_thread_ran_arch();
94}
95
96#ifdef CONFIG_FPU_LAZY
97void scheduler_fpu_lazy_request(void)
98{
99 fpu_enable();
100 spinlock_lock(&CPU->lock);
101
102 /* Save old context */
103 if (CPU->fpu_owner != NULL) {
104 spinlock_lock(&CPU->fpu_owner->lock);
105 fpu_context_save(CPU->fpu_owner->saved_fpu_context);
106 /* don't prevent migration */
107 CPU->fpu_owner->fpu_context_engaged=0;
108 spinlock_unlock(&CPU->fpu_owner->lock);
109 }
110
111 spinlock_lock(&THREAD->lock);
112 if (THREAD->fpu_context_exists) {
113 fpu_context_restore(THREAD->saved_fpu_context);
114 } else {
115 /* Allocate FPU context */
116 if (!THREAD->saved_fpu_context) {
117 /* Might sleep */
118 spinlock_unlock(&THREAD->lock);
119 THREAD->saved_fpu_context = slab_alloc(fpu_context_slab,
120 0);
121 spinlock_lock(&THREAD->lock);
122 }
123 fpu_init();
124 THREAD->fpu_context_exists=1;
125 }
126 CPU->fpu_owner=THREAD;
127 THREAD->fpu_context_engaged = 1;
128 spinlock_unlock(&THREAD->lock);
129
130 spinlock_unlock(&CPU->lock);
131}
132#endif
133
134/** Initialize scheduler
135 *
136 * Initialize kernel scheduler.
137 *
138 */
139void scheduler_init(void)
140{
141}
142
143/** Get thread to be scheduled
144 *
145 * Get the optimal thread to be scheduled
146 * according to thread accounting and scheduler
147 * policy.
148 *
149 * @return Thread to be scheduled.
150 *
151 */
152static thread_t *find_best_thread(void)
153{
154 thread_t *t;
155 runq_t *r;
156 int i;
157
158 ASSERT(CPU != NULL);
159
160loop:
161 interrupts_enable();
162
163 if (atomic_get(&CPU->nrdy) == 0) {
164 /*
165 * For there was nothing to run, the CPU goes to sleep
166 * until a hardware interrupt or an IPI comes.
167 * This improves energy saving and hyperthreading.
168 */
169
170 /*
171 * An interrupt might occur right now and wake up a thread.
172 * In such case, the CPU will continue to go to sleep
173 * even though there is a runnable thread.
174 */
175
176 cpu_sleep();
177 goto loop;
178 }
179
180 interrupts_disable();
181
182 for (i = 0; i<RQ_COUNT; i++) {
183 r = &CPU->rq[i];
184 spinlock_lock(&r->lock);
185 if (r->n == 0) {
186 /*
187 * If this queue is empty, try a lower-priority queue.
188 */
189 spinlock_unlock(&r->lock);
190 continue;
191 }
192
193 atomic_dec(&CPU->nrdy);
194 atomic_dec(&nrdy);
195 r->n--;
196
197 /*
198 * Take the first thread from the queue.
199 */
200 t = list_get_instance(r->rq_head.next, thread_t, rq_link);
201 list_remove(&t->rq_link);
202
203 spinlock_unlock(&r->lock);
204
205 spinlock_lock(&t->lock);
206 t->cpu = CPU;
207
208 t->ticks = us2ticks((i+1)*10000);
209 t->priority = i; /* correct rq index */
210
211 /*
212 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
213 */
214 t->flags &= ~X_STOLEN;
215 spinlock_unlock(&t->lock);
216
217 return t;
218 }
219 goto loop;
220
221}
222
223/** Prevent rq starvation
224 *
225 * Prevent low priority threads from starving in rq's.
226 *
227 * When the function decides to relink rq's, it reconnects
228 * respective pointers so that in result threads with 'pri'
229 * greater or equal 'start' are moved to a higher-priority queue.
230 *
231 * @param start Threshold priority.
232 *
233 */
234static void relink_rq(int start)
235{
236 link_t head;
237 runq_t *r;
238 int i, n;
239
240 list_initialize(&head);
241 spinlock_lock(&CPU->lock);
242 if (CPU->needs_relink > NEEDS_RELINK_MAX) {
243 for (i = start; i<RQ_COUNT-1; i++) {
244 /* remember and empty rq[i + 1] */
245 r = &CPU->rq[i + 1];
246 spinlock_lock(&r->lock);
247 list_concat(&head, &r->rq_head);
248 n = r->n;
249 r->n = 0;
250 spinlock_unlock(&r->lock);
251
252 /* append rq[i + 1] to rq[i] */
253 r = &CPU->rq[i];
254 spinlock_lock(&r->lock);
255 list_concat(&r->rq_head, &head);
256 r->n += n;
257 spinlock_unlock(&r->lock);
258 }
259 CPU->needs_relink = 0;
260 }
261 spinlock_unlock(&CPU->lock);
262
263}
264
265/** The scheduler
266 *
267 * The thread scheduling procedure.
268 * Passes control directly to
269 * scheduler_separated_stack().
270 *
271 */
272void scheduler(void)
273{
274 volatile ipl_t ipl;
275
276 ASSERT(CPU != NULL);
277
278 ipl = interrupts_disable();
279
280 if (atomic_get(&haltstate))
281 halt();
282
283 if (THREAD) {
284 spinlock_lock(&THREAD->lock);
285#ifndef CONFIG_FPU_LAZY
286 fpu_context_save(THREAD->saved_fpu_context);
287#endif
288 if (!context_save(&THREAD->saved_context)) {
289 /*
290 * This is the place where threads leave scheduler();
291 */
292 spinlock_unlock(&THREAD->lock);
293 interrupts_restore(THREAD->saved_context.ipl);
294 return;
295 }
296
297 /*
298 * Interrupt priority level of preempted thread is recorded here
299 * to facilitate scheduler() invocations from interrupts_disable()'d
300 * code (e.g. waitq_sleep_timeout()).
301 */
302 THREAD->saved_context.ipl = ipl;
303 }
304
305 /*
306 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
307 * and preemption counter. At this point THE could be coming either
308 * from THREAD's or CPU's stack.
309 */
310 the_copy(THE, (the_t *) CPU->stack);
311
312 /*
313 * We may not keep the old stack.
314 * Reason: If we kept the old stack and got blocked, for instance, in
315 * find_best_thread(), the old thread could get rescheduled by another
316 * CPU and overwrite the part of its own stack that was also used by
317 * the scheduler on this CPU.
318 *
319 * Moreover, we have to bypass the compiler-generated POP sequence
320 * which is fooled by SP being set to the very top of the stack.
321 * Therefore the scheduler() function continues in
322 * scheduler_separated_stack().
323 */
324 context_save(&CPU->saved_context);
325 context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), (__address) CPU->stack, CPU_STACK_SIZE);
326 context_restore(&CPU->saved_context);
327 /* not reached */
328}
329
330/** Scheduler stack switch wrapper
331 *
332 * Second part of the scheduler() function
333 * using new stack. Handling the actual context
334 * switch to a new thread.
335 *
336 * Assume THREAD->lock is held.
337 */
338void scheduler_separated_stack(void)
339{
340 int priority;
341
342 ASSERT(CPU != NULL);
343
344 if (THREAD) {
345 /* must be run after the switch to scheduler stack */
346 after_thread_ran();
347
348 switch (THREAD->state) {
349 case Running:
350 THREAD->state = Ready;
351 spinlock_unlock(&THREAD->lock);
352 thread_ready(THREAD);
353 break;
354
355 case Exiting:
356 thread_destroy(THREAD);
357 break;
358
359 case Sleeping:
360 /*
361 * Prefer the thread after it's woken up.
362 */
363 THREAD->priority = -1;
364
365 /*
366 * We need to release wq->lock which we locked in waitq_sleep().
367 * Address of wq->lock is kept in THREAD->sleep_queue.
368 */
369 spinlock_unlock(&THREAD->sleep_queue->lock);
370
371 /*
372 * Check for possible requests for out-of-context invocation.
373 */
374 if (THREAD->call_me) {
375 THREAD->call_me(THREAD->call_me_with);
376 THREAD->call_me = NULL;
377 THREAD->call_me_with = NULL;
378 }
379
380 spinlock_unlock(&THREAD->lock);
381
382 break;
383
384 default:
385 /*
386 * Entering state is unexpected.
387 */
388 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
389 break;
390 }
391
392 THREAD = NULL;
393 }
394
395 THREAD = find_best_thread();
396
397 spinlock_lock(&THREAD->lock);
398 priority = THREAD->priority;
399 spinlock_unlock(&THREAD->lock);
400
401 relink_rq(priority);
402
403 spinlock_lock(&THREAD->lock);
404
405 /*
406 * If both the old and the new task are the same, lots of work is avoided.
407 */
408 if (TASK != THREAD->task) {
409 as_t *as1 = NULL;
410 as_t *as2;
411
412 if (TASK) {
413 spinlock_lock(&TASK->lock);
414 as1 = TASK->as;
415 spinlock_unlock(&TASK->lock);
416 }
417
418 spinlock_lock(&THREAD->task->lock);
419 as2 = THREAD->task->as;
420 spinlock_unlock(&THREAD->task->lock);
421
422 /*
423 * Note that it is possible for two tasks to share one address space.
424 */
425 if (as1 != as2) {
426 /*
427 * Both tasks and address spaces are different.
428 * Replace the old one with the new one.
429 */
430 as_switch(as1, as2);
431 }
432 TASK = THREAD->task;
433 }
434
435 THREAD->state = Running;
436
437#ifdef SCHEDULER_VERBOSE
438 printf("cpu%d: tid %d (priority=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks, atomic_get(&CPU->nrdy));
439#endif
440
441 /*
442 * Some architectures provide late kernel PA2KA(identity)
443 * mapping in a page fault handler. However, the page fault
444 * handler uses the kernel stack of the running thread and
445 * therefore cannot be used to map it. The kernel stack, if
446 * necessary, is to be mapped in before_thread_runs(). This
447 * function must be executed before the switch to the new stack.
448 */
449 before_thread_runs();
450
451 /*
452 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
453 */
454 the_copy(THE, (the_t *) THREAD->kstack);
455
456 context_restore(&THREAD->saved_context);
457 /* not reached */
458}
459
460#ifdef CONFIG_SMP
461/** Load balancing thread
462 *
463 * SMP load balancing thread, supervising thread supplies
464 * for the CPU it's wired to.
465 *
466 * @param arg Generic thread argument (unused).
467 *
468 */
469void kcpulb(void *arg)
470{
471 thread_t *t;
472 int count, average, i, j, k = 0;
473 ipl_t ipl;
474
475loop:
476 /*
477 * Work in 1s intervals.
478 */
479 thread_sleep(1);
480
481not_satisfied:
482 /*
483 * Calculate the number of threads that will be migrated/stolen from
484 * other CPU's. Note that situation can have changed between two
485 * passes. Each time get the most up to date counts.
486 */
487 average = atomic_get(&nrdy) / config.cpu_active + 1;
488 count = average - atomic_get(&CPU->nrdy);
489
490 if (count <= 0)
491 goto satisfied;
492
493 /*
494 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
495 */
496 for (j=RQ_COUNT-1; j >= 0; j--) {
497 for (i=0; i < config.cpu_active; i++) {
498 link_t *l;
499 runq_t *r;
500 cpu_t *cpu;
501
502 cpu = &cpus[(i + k) % config.cpu_active];
503
504 /*
505 * Not interested in ourselves.
506 * Doesn't require interrupt disabling for kcpulb is X_WIRED.
507 */
508 if (CPU == cpu)
509 continue;
510 if (atomic_get(&cpu->nrdy) <= average)
511 continue;
512
513 ipl = interrupts_disable();
514 r = &cpu->rq[j];
515 spinlock_lock(&r->lock);
516 if (r->n == 0) {
517 spinlock_unlock(&r->lock);
518 interrupts_restore(ipl);
519 continue;
520 }
521
522 t = NULL;
523 l = r->rq_head.prev; /* search rq from the back */
524 while (l != &r->rq_head) {
525 t = list_get_instance(l, thread_t, rq_link);
526 /*
527 * We don't want to steal CPU-wired threads neither threads already stolen.
528 * The latter prevents threads from migrating between CPU's without ever being run.
529 * We don't want to steal threads whose FPU context is still in CPU.
530 */
531 spinlock_lock(&t->lock);
532 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
533 /*
534 * Remove t from r.
535 */
536 spinlock_unlock(&t->lock);
537
538 atomic_dec(&cpu->nrdy);
539 atomic_dec(&nrdy);
540
541 r->n--;
542 list_remove(&t->rq_link);
543
544 break;
545 }
546 spinlock_unlock(&t->lock);
547 l = l->prev;
548 t = NULL;
549 }
550 spinlock_unlock(&r->lock);
551
552 if (t) {
553 /*
554 * Ready t on local CPU
555 */
556 spinlock_lock(&t->lock);
557#ifdef KCPULB_VERBOSE
558 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, atomic_get(&CPU->nrdy), atomic_get(&nrdy) / config.cpu_active);
559#endif
560 t->flags |= X_STOLEN;
561 spinlock_unlock(&t->lock);
562
563 thread_ready(t);
564
565 interrupts_restore(ipl);
566
567 if (--count == 0)
568 goto satisfied;
569
570 /*
571 * We are not satisfied yet, focus on another CPU next time.
572 */
573 k++;
574
575 continue;
576 }
577 interrupts_restore(ipl);
578 }
579 }
580
581 if (atomic_get(&CPU->nrdy)) {
582 /*
583 * Be a little bit light-weight and let migrated threads run.
584 */
585 scheduler();
586 } else {
587 /*
588 * We failed to migrate a single thread.
589 * Give up this turn.
590 */
591 goto loop;
592 }
593
594 goto not_satisfied;
595
596satisfied:
597 goto loop;
598}
599
600#endif /* CONFIG_SMP */
601
602
603/** Print information about threads & scheduler queues */
604void sched_print_list(void)
605{
606 ipl_t ipl;
607 int cpu,i;
608 runq_t *r;
609 thread_t *t;
610 link_t *cur;
611
612 /* We are going to mess with scheduler structures,
613 * let's not be interrupted */
614 ipl = interrupts_disable();
615 printf("Scheduler dump:\n");
616 for (cpu=0;cpu < config.cpu_count; cpu++) {
617
618 if (!cpus[cpu].active)
619 continue;
620
621 spinlock_lock(&cpus[cpu].lock);
622 printf("cpu%d: nrdy: %d, needs_relink: %d\n",
623 cpus[cpu].id, atomic_get(&cpus[cpu].nrdy), cpus[cpu].needs_relink);
624
625 for (i=0; i<RQ_COUNT; i++) {
626 r = &cpus[cpu].rq[i];
627 spinlock_lock(&r->lock);
628 if (!r->n) {
629 spinlock_unlock(&r->lock);
630 continue;
631 }
632 printf("\trq[%d]: ", i);
633 for (cur=r->rq_head.next; cur!=&r->rq_head; cur=cur->next) {
634 t = list_get_instance(cur, thread_t, rq_link);
635 printf("%d(%s) ", t->tid,
636 thread_states[t->state]);
637 }
638 printf("\n");
639 spinlock_unlock(&r->lock);
640 }
641 spinlock_unlock(&cpus[cpu].lock);
642 }
643
644 interrupts_restore(ipl);
645}
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