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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
volatile int nrdy;
48
 
107 decky 49
 
118 jermar 50
/** Take actions before new thread runs
107 decky 51
 *
118 jermar 52
 * Perform actions that need to be
53
 * taken before the newly selected
54
 * tread is passed control.
107 decky 55
 *
56
 */
52 vana 57
void before_thread_runs(void)
58
{
59
    before_thread_runs_arch();
57 vana 60
    fpu_context_restore(&(THREAD->saved_fpu_context));
52 vana 61
}
62
 
63
 
107 decky 64
/** Initialize scheduler
65
 *
66
 * Initialize kernel scheduler.
67
 *
68
 */
1 jermar 69
void scheduler_init(void)
70
{
71
}
72
 
107 decky 73
 
74
/** Get thread to be scheduled
75
 *
76
 * Get the optimal thread to be scheduled
109 jermar 77
 * according to thread accounting and scheduler
107 decky 78
 * policy.
79
 *
80
 * @return Thread to be scheduled.
81
 *
82
 */
1 jermar 83
struct thread *find_best_thread(void)
84
{
85
    thread_t *t;
86
    runq_t *r;
87
    int i, n;
88
 
89
loop:
90
    cpu_priority_high();
91
 
15 jermar 92
    spinlock_lock(&CPU->lock);
93
    n = CPU->nrdy;
94
    spinlock_unlock(&CPU->lock);
1 jermar 95
 
96
    cpu_priority_low();
97
 
98
    if (n == 0) {
99
        #ifdef __SMP__
100
        /*
101
         * If the load balancing thread is not running, wake it up and
102
         * set CPU-private flag that the kcpulb has been started.
103
         */
15 jermar 104
        if (test_and_set(&CPU->kcpulbstarted) == 0) {
125 jermar 105
            waitq_wakeup(&CPU->kcpulb_wq, 0);
1 jermar 106
            goto loop;
107
        }
108
        #endif /* __SMP__ */
109
 
110
        /*
111
         * For there was nothing to run, the CPU goes to sleep
112
         * until a hardware interrupt or an IPI comes.
113
         * This improves energy saving and hyperthreading.
114
         * On the other hand, several hardware interrupts can be ignored.
115
         */
116
         cpu_sleep();
117
         goto loop;
118
    }
119
 
120
    cpu_priority_high();
114 jermar 121
 
122
    i = 0;
123
retry:
124
    for (; i<RQ_COUNT; i++) {
15 jermar 125
        r = &CPU->rq[i];
1 jermar 126
        spinlock_lock(&r->lock);
127
        if (r->n == 0) {
128
            /*
129
             * If this queue is empty, try a lower-priority queue.
130
             */
131
            spinlock_unlock(&r->lock);
132
            continue;
133
        }
134
 
115 jermar 135
        /* avoid deadlock with relink_rq() */
114 jermar 136
        if (!spinlock_trylock(&CPU->lock)) {
137
            /*
138
             * Unlock r and try again.
139
             */
140
            spinlock_unlock(&r->lock);
141
            goto retry;
142
        }
15 jermar 143
        CPU->nrdy--;
144
        spinlock_unlock(&CPU->lock);
1 jermar 145
 
114 jermar 146
        atomic_dec(&nrdy);
1 jermar 147
        r->n--;
148
 
149
        /*
150
         * Take the first thread from the queue.
151
         */
152
        t = list_get_instance(r->rq_head.next, thread_t, rq_link);
153
        list_remove(&t->rq_link);
154
 
155
        spinlock_unlock(&r->lock);
156
 
157
        spinlock_lock(&t->lock);
15 jermar 158
        t->cpu = CPU;
1 jermar 159
 
160
        t->ticks = us2ticks((i+1)*10000);
161
        t->pri = i; /* eventually correct rq index */
162
 
163
        /*
164
         * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
165
         */
166
        t->flags &= ~X_STOLEN;
167
        spinlock_unlock(&t->lock);
168
 
169
        return t;
170
    }
171
    goto loop;
172
 
173
}
174
 
107 decky 175
 
176
/** Prevent rq starvation
177
 *
178
 * Prevent low priority threads from starving in rq's.
179
 *
180
 * When the function decides to relink rq's, it reconnects
181
 * respective pointers so that in result threads with 'pri'
182
 * greater or equal 'start' are moved to a higher-priority queue.
183
 *
184
 * @param start Threshold priority.
185
 *
1 jermar 186
 */
187
void relink_rq(int start)
188
{
189
    link_t head;
190
    runq_t *r;
191
    int i, n;
192
 
193
    list_initialize(&head);
15 jermar 194
    spinlock_lock(&CPU->lock);
195
    if (CPU->needs_relink > NEEDS_RELINK_MAX) {
1 jermar 196
        for (i = start; i<RQ_COUNT-1; i++) {
197
            /* remember and empty rq[i + 1] */
15 jermar 198
            r = &CPU->rq[i + 1];
1 jermar 199
            spinlock_lock(&r->lock);
200
            list_concat(&head, &r->rq_head);
201
            n = r->n;
202
            r->n = 0;
203
            spinlock_unlock(&r->lock);
204
 
205
            /* append rq[i + 1] to rq[i] */
15 jermar 206
            r = &CPU->rq[i];
1 jermar 207
            spinlock_lock(&r->lock);
208
            list_concat(&r->rq_head, &head);
209
            r->n += n;
210
            spinlock_unlock(&r->lock);
211
        }
15 jermar 212
        CPU->needs_relink = 0;
1 jermar 213
    }
15 jermar 214
    spinlock_unlock(&CPU->lock);               
1 jermar 215
 
216
}
217
 
107 decky 218
 
219
/** The scheduler
220
 *
221
 * The thread scheduling procedure.
222
 *
1 jermar 223
 */
224
void scheduler(void)
225
{
226
    volatile pri_t pri;
227
 
228
    pri = cpu_priority_high();
229
 
230
    if (haltstate)
231
        halt();
232
 
15 jermar 233
    if (THREAD) {
234
        spinlock_lock(&THREAD->lock);
57 vana 235
        fpu_context_save(&(THREAD->saved_fpu_context));
15 jermar 236
        if (!context_save(&THREAD->saved_context)) {
1 jermar 237
            /*
238
             * This is the place where threads leave scheduler();
239
             */
22 jermar 240
            before_thread_runs();
125 jermar 241
            spinlock_unlock(&THREAD->lock);
15 jermar 242
            cpu_priority_restore(THREAD->saved_context.pri);
1 jermar 243
            return;
244
        }
15 jermar 245
        THREAD->saved_context.pri = pri;
1 jermar 246
    }
247
 
248
    /*
249
     * We may not keep the old stack.
250
     * Reason: If we kept the old stack and got blocked, for instance, in
251
     * find_best_thread(), the old thread could get rescheduled by another
252
     * CPU and overwrite the part of its own stack that was also used by
253
     * the scheduler on this CPU.
254
     *
255
     * Moreover, we have to bypass the compiler-generated POP sequence
256
     * which is fooled by SP being set to the very top of the stack.
257
     * Therefore the scheduler() function continues in
258
     * scheduler_separated_stack().
259
     */
15 jermar 260
    context_save(&CPU->saved_context);
97 jermar 261
    context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
15 jermar 262
    context_restore(&CPU->saved_context);
1 jermar 263
    /* not reached */
264
}
265
 
107 decky 266
 
267
/** Scheduler stack switch wrapper
268
 *
269
 * Second part of the scheduler() function
270
 * using new stack. Handling the actual context
271
 * switch to a new thread.
272
 *
273
 */
1 jermar 274
void scheduler_separated_stack(void)
275
{
276
    int priority;
277
 
15 jermar 278
    if (THREAD) {
279
        switch (THREAD->state) {
1 jermar 280
            case Running:
125 jermar 281
            THREAD->state = Ready;
282
            spinlock_unlock(&THREAD->lock);
283
            thread_ready(THREAD);
284
            break;
1 jermar 285
 
286
            case Exiting:
125 jermar 287
            frame_free((__address) THREAD->kstack);
288
            if (THREAD->ustack) {
289
                frame_free((__address) THREAD->ustack);
290
            }
1 jermar 291
 
125 jermar 292
            /*
293
             * Detach from the containing task.
294
             */
295
            spinlock_lock(&TASK->lock);
296
            list_remove(&THREAD->th_link);
297
            spinlock_unlock(&TASK->lock);
73 vana 298
 
125 jermar 299
            spinlock_unlock(&THREAD->lock);
300
 
301
            spinlock_lock(&threads_lock);
302
            list_remove(&THREAD->threads_link);
303
            spinlock_unlock(&threads_lock);
73 vana 304
 
125 jermar 305
            spinlock_lock(&CPU->lock);
306
            if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
307
            spinlock_unlock(&CPU->lock);
308
 
309
            free(THREAD);
310
 
311
            break;
312
 
1 jermar 313
            case Sleeping:
125 jermar 314
            /*
315
             * Prefer the thread after it's woken up.
316
             */
317
            THREAD->pri = -1;
1 jermar 318
 
125 jermar 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);
1 jermar 324
 
125 jermar 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
            }
1 jermar 333
 
125 jermar 334
            spinlock_unlock(&THREAD->lock);
1 jermar 335
 
125 jermar 336
            break;
337
 
1 jermar 338
            default:
125 jermar 339
            /*
340
             * Entering state is unexpected.
341
             */
342
            panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
343
            break;
1 jermar 344
        }
15 jermar 345
        THREAD = NULL;
1 jermar 346
    }
125 jermar 347
 
15 jermar 348
    THREAD = find_best_thread();
1 jermar 349
 
15 jermar 350
    spinlock_lock(&THREAD->lock);
351
    priority = THREAD->pri;
352
    spinlock_unlock(&THREAD->lock);
1 jermar 353
 
354
    relink_rq(priority);       
355
 
15 jermar 356
    spinlock_lock(&THREAD->lock);  
1 jermar 357
 
358
    /*
359
     * If both the old and the new task are the same, lots of work is avoided.
360
     */
15 jermar 361
    if (TASK != THREAD->task) {
1 jermar 362
        vm_t *m1 = NULL;
363
        vm_t *m2;
364
 
15 jermar 365
        if (TASK) {
366
            spinlock_lock(&TASK->lock);
367
            m1 = TASK->vm;
368
            spinlock_unlock(&TASK->lock);
1 jermar 369
        }
370
 
15 jermar 371
        spinlock_lock(&THREAD->task->lock);
372
        m2 = THREAD->task->vm;
373
        spinlock_unlock(&THREAD->task->lock);
1 jermar 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
        }
15 jermar 388
        TASK = THREAD->task;   
1 jermar 389
    }
390
 
15 jermar 391
    THREAD->state = Running;
1 jermar 392
 
393
    #ifdef SCHEDULER_VERBOSE
15 jermar 394
    printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
1 jermar 395
    #endif  
396
 
15 jermar 397
    context_restore(&THREAD->saved_context);
1 jermar 398
    /* not reached */
399
}
400
 
107 decky 401
 
1 jermar 402
#ifdef __SMP__
107 decky 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
 *
1 jermar 410
 */
411
void kcpulb(void *arg)
412
{
413
    thread_t *t;
414
    int count, i, j, k = 0;
415
    pri_t pri;
416
 
417
loop:
418
    /*
419
     * Sleep until there's some work to do.
420
     */
15 jermar 421
    waitq_sleep(&CPU->kcpulb_wq);
1 jermar 422
 
423
not_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();
15 jermar 430
    spinlock_lock(&CPU->lock);
1 jermar 431
    count = nrdy / config.cpu_active;
15 jermar 432
    count -= CPU->nrdy;
433
    spinlock_unlock(&CPU->lock);
1 jermar 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
             */
15 jermar 454
            if (CPU == cpu)
115 jermar 455
                continue;              
1 jermar 456
 
457
restart:        pri = cpu_priority_high();
115 jermar 458
            r = &cpu->rq[j];
1 jermar 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
                /*
125 jermar 471
                 * We don't want to steal CPU-wired threads neither threads already stolen.
1 jermar 472
                 * The latter prevents threads from migrating between CPU's without ever being run.
125 jermar 473
                 * We don't want to steal threads whose FPU context is still in CPU.
73 vana 474
                 */
1 jermar 475
                spinlock_lock(&t->lock);
73 vana 476
                if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
115 jermar 477
 
1 jermar 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
 
111 palkovsky 497
                    atomic_dec(&nrdy);
1 jermar 498
 
125 jermar 499
                    r->n--;
1 jermar 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
15 jermar 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);
1 jermar 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
                /*
125 jermar 529
                 * We are not satisfied yet, focus on another CPU next time.
1 jermar 530
                 */
531
                k++;
532
 
533
                continue;
534
            }
535
            cpu_priority_restore(pri);
536
        }
537
    }
538
 
15 jermar 539
    if (CPU->nrdy) {
1 jermar 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;
125 jermar 554
 
1 jermar 555
satisfied:
556
    /*
557
     * Tell find_best_thread() to wake us up later again.
558
     */
15 jermar 559
    CPU->kcpulbstarted = 0;
1 jermar 560
    goto loop;
561
}
562
 
563
#endif /* __SMP__ */