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1 jermar 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>
68 decky 40
#include <panic.h>
1 jermar 41
#include <typedefs.h>
42
#include <mm/page.h>
43
#include <synch/spinlock.h>
76 jermar 44
#include <arch/faddr.h>
111 palkovsky 45
#include <arch/atomic.h>
1 jermar 46
 
47
/*
48
 * NOTE ON ATOMIC READS:
49
 * Some architectures cannot read __u32 atomically.
50
 * For that reason, all accesses to nrdy and the likes must be protected by spinlock.
51
 */
52
 
53
volatile int nrdy;
54
 
107 decky 55
 
56
/** Initialize context switching
57
 *
58
 * Initialize context switching and lazy FPU
59
 * context switching.
60
 *
61
 */
52 vana 62
void before_thread_runs(void)
63
{
64
    before_thread_runs_arch();
57 vana 65
    fpu_context_restore(&(THREAD->saved_fpu_context));
52 vana 66
}
67
 
68
 
107 decky 69
/** Initialize scheduler
70
 *
71
 * Initialize kernel scheduler.
72
 *
73
 */
1 jermar 74
void scheduler_init(void)
75
{
76
}
77
 
107 decky 78
 
79
/** Get thread to be scheduled
80
 *
81
 * Get the optimal thread to be scheduled
109 jermar 82
 * according to thread accounting and scheduler
107 decky 83
 * policy.
84
 *
85
 * @return Thread to be scheduled.
86
 *
87
 */
1 jermar 88
struct thread *find_best_thread(void)
89
{
90
    thread_t *t;
91
    runq_t *r;
92
    int i, n;
93
 
94
loop:
95
    cpu_priority_high();
96
 
15 jermar 97
    spinlock_lock(&CPU->lock);
98
    n = CPU->nrdy;
99
    spinlock_unlock(&CPU->lock);
1 jermar 100
 
101
    cpu_priority_low();
102
 
103
    if (n == 0) {
104
        #ifdef __SMP__
105
        /*
106
         * If the load balancing thread is not running, wake it up and
107
         * set CPU-private flag that the kcpulb has been started.
108
         */
15 jermar 109
        if (test_and_set(&CPU->kcpulbstarted) == 0) {
110
                waitq_wakeup(&CPU->kcpulb_wq, 0);
1 jermar 111
            goto loop;
112
        }
113
        #endif /* __SMP__ */
114
 
115
        /*
116
         * For there was nothing to run, the CPU goes to sleep
117
         * until a hardware interrupt or an IPI comes.
118
         * This improves energy saving and hyperthreading.
119
         * On the other hand, several hardware interrupts can be ignored.
120
         */
121
         cpu_sleep();
122
         goto loop;
123
    }
124
 
125
    cpu_priority_high();
126
 
127
    for (i = 0; i<RQ_COUNT; i++) {
15 jermar 128
        r = &CPU->rq[i];
1 jermar 129
        spinlock_lock(&r->lock);
130
        if (r->n == 0) {
131
            /*
132
             * If this queue is empty, try a lower-priority queue.
133
             */
134
            spinlock_unlock(&r->lock);
135
            continue;
136
        }
137
 
111 palkovsky 138
        atomic_dec(&nrdy);
1 jermar 139
 
15 jermar 140
        spinlock_lock(&CPU->lock);
141
        CPU->nrdy--;
142
        spinlock_unlock(&CPU->lock);
1 jermar 143
 
144
        r->n--;
145
 
146
        /*
147
         * Take the first thread from the queue.
148
         */
149
        t = list_get_instance(r->rq_head.next, thread_t, rq_link);
150
        list_remove(&t->rq_link);
151
 
152
        spinlock_unlock(&r->lock);
153
 
154
        spinlock_lock(&t->lock);
15 jermar 155
        t->cpu = CPU;
1 jermar 156
 
157
        t->ticks = us2ticks((i+1)*10000);
158
        t->pri = i; /* eventually correct rq index */
159
 
160
        /*
161
         * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
162
         */
163
        t->flags &= ~X_STOLEN;
164
        spinlock_unlock(&t->lock);
165
 
166
        return t;
167
    }
168
    goto loop;
169
 
170
}
171
 
107 decky 172
 
173
/** Prevent rq starvation
174
 *
175
 * Prevent low priority threads from starving in rq's.
176
 *
177
 * When the function decides to relink rq's, it reconnects
178
 * respective pointers so that in result threads with 'pri'
179
 * greater or equal 'start' are moved to a higher-priority queue.
180
 *
181
 * @param start Threshold priority.
182
 *
1 jermar 183
 */
184
void relink_rq(int start)
185
{
186
    link_t head;
187
    runq_t *r;
188
    int i, n;
189
 
190
    list_initialize(&head);
15 jermar 191
    spinlock_lock(&CPU->lock);
192
    if (CPU->needs_relink > NEEDS_RELINK_MAX) {
1 jermar 193
        for (i = start; i<RQ_COUNT-1; i++) {
194
            /* remember and empty rq[i + 1] */
15 jermar 195
            r = &CPU->rq[i + 1];
1 jermar 196
            spinlock_lock(&r->lock);
197
            list_concat(&head, &r->rq_head);
198
            n = r->n;
199
            r->n = 0;
200
            spinlock_unlock(&r->lock);
201
 
202
            /* append rq[i + 1] to rq[i] */
15 jermar 203
            r = &CPU->rq[i];
1 jermar 204
            spinlock_lock(&r->lock);
205
            list_concat(&r->rq_head, &head);
206
            r->n += n;
207
            spinlock_unlock(&r->lock);
208
        }
15 jermar 209
        CPU->needs_relink = 0;
1 jermar 210
    }
15 jermar 211
    spinlock_unlock(&CPU->lock);               
1 jermar 212
 
213
}
214
 
107 decky 215
 
216
/** The scheduler
217
 *
218
 * The thread scheduling procedure.
219
 *
1 jermar 220
 */
221
void scheduler(void)
222
{
223
    volatile pri_t pri;
224
 
225
    pri = cpu_priority_high();
226
 
227
    if (haltstate)
228
        halt();
229
 
15 jermar 230
    if (THREAD) {
231
        spinlock_lock(&THREAD->lock);
57 vana 232
        fpu_context_save(&(THREAD->saved_fpu_context));
15 jermar 233
        if (!context_save(&THREAD->saved_context)) {
1 jermar 234
            /*
235
             * This is the place where threads leave scheduler();
236
             */
22 jermar 237
            before_thread_runs();
15 jermar 238
                spinlock_unlock(&THREAD->lock);
239
            cpu_priority_restore(THREAD->saved_context.pri);
1 jermar 240
            return;
241
        }
15 jermar 242
        THREAD->saved_context.pri = pri;
1 jermar 243
    }
244
 
245
    /*
246
     * We may not keep the old stack.
247
     * Reason: If we kept the old stack and got blocked, for instance, in
248
     * find_best_thread(), the old thread could get rescheduled by another
249
     * CPU and overwrite the part of its own stack that was also used by
250
     * the scheduler on this CPU.
251
     *
252
     * Moreover, we have to bypass the compiler-generated POP sequence
253
     * which is fooled by SP being set to the very top of the stack.
254
     * Therefore the scheduler() function continues in
255
     * scheduler_separated_stack().
256
     */
15 jermar 257
    context_save(&CPU->saved_context);
97 jermar 258
    context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
15 jermar 259
    context_restore(&CPU->saved_context);
1 jermar 260
    /* not reached */
261
}
262
 
107 decky 263
 
264
/** Scheduler stack switch wrapper
265
 *
266
 * Second part of the scheduler() function
267
 * using new stack. Handling the actual context
268
 * switch to a new thread.
269
 *
270
 */
1 jermar 271
void scheduler_separated_stack(void)
272
{
273
    int priority;
274
 
15 jermar 275
    if (THREAD) {
276
        switch (THREAD->state) {
1 jermar 277
            case Running:
15 jermar 278
                THREAD->state = Ready;
279
                spinlock_unlock(&THREAD->lock);
280
                thread_ready(THREAD);
1 jermar 281
                break;
282
 
283
            case Exiting:
15 jermar 284
                frame_free((__address) THREAD->kstack);
285
                if (THREAD->ustack) {
286
                    frame_free((__address) THREAD->ustack);
1 jermar 287
                }
288
 
289
                /*
290
                 * Detach from the containing task.
291
                 */
15 jermar 292
                spinlock_lock(&TASK->lock);
293
                list_remove(&THREAD->th_link);
294
                spinlock_unlock(&TASK->lock);
1 jermar 295
 
15 jermar 296
                spinlock_unlock(&THREAD->lock);
1 jermar 297
 
298
                spinlock_lock(&threads_lock);
15 jermar 299
                list_remove(&THREAD->threads_link);
1 jermar 300
                spinlock_unlock(&threads_lock);
73 vana 301
 
99 jermar 302
                spinlock_lock(&CPU->lock);
303
                if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
304
                spinlock_unlock(&CPU->lock);
73 vana 305
 
1 jermar 306
 
15 jermar 307
                free(THREAD);
1 jermar 308
 
309
                break;
310
 
311
            case Sleeping:
312
                /*
313
                 * Prefer the thread after it's woken up.
314
                 */
15 jermar 315
                THREAD->pri = -1;
1 jermar 316
 
317
                /*
318
                 * We need to release wq->lock which we locked in waitq_sleep().
15 jermar 319
                 * Address of wq->lock is kept in THREAD->sleep_queue.
1 jermar 320
                 */
15 jermar 321
                spinlock_unlock(&THREAD->sleep_queue->lock);
1 jermar 322
 
323
                /*
324
                 * Check for possible requests for out-of-context invocation.
325
                 */
15 jermar 326
                if (THREAD->call_me) {
327
                    THREAD->call_me(THREAD->call_me_with);
328
                    THREAD->call_me = NULL;
329
                    THREAD->call_me_with = NULL;
1 jermar 330
                }
331
 
15 jermar 332
                spinlock_unlock(&THREAD->lock);
1 jermar 333
 
334
                break;
335
 
336
            default:
337
                /*
338
                 * Entering state is unexpected.
339
                 */
15 jermar 340
                panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
1 jermar 341
                break;
342
        }
15 jermar 343
        THREAD = NULL;
1 jermar 344
    }
345
 
15 jermar 346
    THREAD = find_best_thread();
1 jermar 347
 
15 jermar 348
    spinlock_lock(&THREAD->lock);
349
    priority = THREAD->pri;
350
    spinlock_unlock(&THREAD->lock);
1 jermar 351
 
352
    relink_rq(priority);       
353
 
15 jermar 354
    spinlock_lock(&THREAD->lock);  
1 jermar 355
 
356
    /*
357
     * If both the old and the new task are the same, lots of work is avoided.
358
     */
15 jermar 359
    if (TASK != THREAD->task) {
1 jermar 360
        vm_t *m1 = NULL;
361
        vm_t *m2;
362
 
15 jermar 363
        if (TASK) {
364
            spinlock_lock(&TASK->lock);
365
            m1 = TASK->vm;
366
            spinlock_unlock(&TASK->lock);
1 jermar 367
        }
368
 
15 jermar 369
        spinlock_lock(&THREAD->task->lock);
370
        m2 = THREAD->task->vm;
371
        spinlock_unlock(&THREAD->task->lock);
1 jermar 372
 
373
        /*
374
         * Note that it is possible for two tasks to share one vm mapping.
375
         */
376
        if (m1 != m2) {
377
            /*
378
             * Both tasks and vm mappings are different.
379
             * Replace the old one with the new one.
380
             */
381
            if (m1) {
382
                vm_uninstall(m1);
383
            }
384
            vm_install(m2);
385
        }
15 jermar 386
        TASK = THREAD->task;   
1 jermar 387
    }
388
 
15 jermar 389
    THREAD->state = Running;
1 jermar 390
 
391
    #ifdef SCHEDULER_VERBOSE
15 jermar 392
    printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
1 jermar 393
    #endif  
394
 
15 jermar 395
    context_restore(&THREAD->saved_context);
1 jermar 396
    /* not reached */
397
}
398
 
107 decky 399
 
1 jermar 400
#ifdef __SMP__
107 decky 401
/** Load balancing thread
402
 *
403
 * SMP load balancing thread, supervising thread supplies
404
 * for the CPU it's wired to.
405
 *
406
 * @param arg Generic thread argument (unused).
407
 *
1 jermar 408
 */
409
void kcpulb(void *arg)
410
{
411
    thread_t *t;
412
    int count, i, j, k = 0;
413
    pri_t pri;
414
 
415
loop:
416
    /*
417
     * Sleep until there's some work to do.
418
     */
15 jermar 419
    waitq_sleep(&CPU->kcpulb_wq);
1 jermar 420
 
421
not_satisfied:
422
    /*
423
     * Calculate the number of threads that will be migrated/stolen from
424
     * other CPU's. Note that situation can have changed between two
425
     * passes. Each time get the most up to date counts.
426
     */
427
    pri = cpu_priority_high();
15 jermar 428
    spinlock_lock(&CPU->lock);
1 jermar 429
    count = nrdy / config.cpu_active;
15 jermar 430
    count -= CPU->nrdy;
431
    spinlock_unlock(&CPU->lock);
1 jermar 432
    cpu_priority_restore(pri);
433
 
434
    if (count <= 0)
435
        goto satisfied;
436
 
437
    /*
438
     * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
439
     */
440
    for (j=RQ_COUNT-1; j >= 0; j--) {
441
        for (i=0; i < config.cpu_active; i++) {
442
            link_t *l;
443
            runq_t *r;
444
            cpu_t *cpu;
445
 
446
            cpu = &cpus[(i + k) % config.cpu_active];
447
            r = &cpu->rq[j];
448
 
449
            /*
450
             * Not interested in ourselves.
451
             * Doesn't require interrupt disabling for kcpulb is X_WIRED.
452
             */
15 jermar 453
            if (CPU == cpu)
1 jermar 454
                continue;
455
 
456
restart:        pri = cpu_priority_high();
457
            spinlock_lock(&r->lock);
458
            if (r->n == 0) {
459
                spinlock_unlock(&r->lock);
460
                cpu_priority_restore(pri);
461
                continue;
462
            }
463
 
464
            t = NULL;
465
            l = r->rq_head.prev;    /* search rq from the back */
466
            while (l != &r->rq_head) {
467
                t = list_get_instance(l, thread_t, rq_link);
468
                /*
469
                     * We don't want to steal CPU-wired threads neither threads already stolen.
470
                 * The latter prevents threads from migrating between CPU's without ever being run.
73 vana 471
                     * We don't want to steal threads whose FPU context is still in CPU
472
                 */
1 jermar 473
                spinlock_lock(&t->lock);
73 vana 474
                if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
1 jermar 475
                    /*
476
                     * Remove t from r.
477
                     */
478
 
479
                    spinlock_unlock(&t->lock);
480
 
481
                    /*
482
                     * Here we have to avoid deadlock with relink_rq(),
483
                     * because it locks cpu and r in a different order than we do.
484
                     */
485
                    if (!spinlock_trylock(&cpu->lock)) {
486
                        /* Release all locks and try again. */
487
                        spinlock_unlock(&r->lock);
488
                        cpu_priority_restore(pri);
489
                        goto restart;
490
                    }
491
                    cpu->nrdy--;
492
                    spinlock_unlock(&cpu->lock);
493
 
111 palkovsky 494
                    atomic_dec(&nrdy);
1 jermar 495
 
496
                        r->n--;
497
                    list_remove(&t->rq_link);
498
 
499
                    break;
500
                }
501
                spinlock_unlock(&t->lock);
502
                l = l->prev;
503
                t = NULL;
504
            }
505
            spinlock_unlock(&r->lock);
506
 
507
            if (t) {
508
                /*
509
                 * Ready t on local CPU
510
                 */
511
                spinlock_lock(&t->lock);
512
                #ifdef KCPULB_VERBOSE
15 jermar 513
                printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
1 jermar 514
                #endif
515
                t->flags |= X_STOLEN;
516
                spinlock_unlock(&t->lock);
517
 
518
                thread_ready(t);
519
 
520
                cpu_priority_restore(pri);
521
 
522
                if (--count == 0)
523
                    goto satisfied;
524
 
525
                /*
526
                             * We are not satisfied yet, focus on another CPU next time.
527
                 */
528
                k++;
529
 
530
                continue;
531
            }
532
            cpu_priority_restore(pri);
533
        }
534
    }
535
 
15 jermar 536
    if (CPU->nrdy) {
1 jermar 537
        /*
538
         * Be a little bit light-weight and let migrated threads run.
539
         */
540
        scheduler();
541
    }
542
    else {
543
        /*
544
         * We failed to migrate a single thread.
545
         * Something more sophisticated should be done.
546
         */
547
        scheduler();
548
    }
549
 
550
    goto not_satisfied;
551
 
552
satisfied:
553
    /*
554
     * Tell find_best_thread() to wake us up later again.
555
     */
15 jermar 556
    CPU->kcpulbstarted = 0;
1 jermar 557
    goto loop;
558
}
559
 
560
#endif /* __SMP__ */