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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>
195 vana 46
#include <print.h>
47
#include <mm/frame.h>
48
#include <mm/heap.h>
227 jermar 49
#include <debug.h>
1 jermar 50
 
227 jermar 51
volatile count_t nrdy;
195 vana 52
 
1 jermar 53
 
118 jermar 54
/** Take actions before new thread runs
107 decky 55
 *
118 jermar 56
 * Perform actions that need to be
57
 * taken before the newly selected
58
 * tread is passed control.
107 decky 59
 *
60
 */
52 vana 61
void before_thread_runs(void)
62
{
63
    before_thread_runs_arch();
57 vana 64
    fpu_context_restore(&(THREAD->saved_fpu_context));
52 vana 65
}
66
 
67
 
107 decky 68
/** Initialize scheduler
69
 *
70
 * Initialize kernel scheduler.
71
 *
72
 */
1 jermar 73
void scheduler_init(void)
74
{
75
}
76
 
107 decky 77
 
78
/** Get thread to be scheduled
79
 *
80
 * Get the optimal thread to be scheduled
109 jermar 81
 * according to thread accounting and scheduler
107 decky 82
 * policy.
83
 *
84
 * @return Thread to be scheduled.
85
 *
86
 */
1 jermar 87
struct thread *find_best_thread(void)
88
{
89
    thread_t *t;
90
    runq_t *r;
91
    int i, n;
92
 
227 jermar 93
    ASSERT(CPU != NULL);
94
 
1 jermar 95
loop:
96
    cpu_priority_high();
97
 
15 jermar 98
    spinlock_lock(&CPU->lock);
99
    n = CPU->nrdy;
100
    spinlock_unlock(&CPU->lock);
1 jermar 101
 
102
    cpu_priority_low();
103
 
104
    if (n == 0) {
105
        #ifdef __SMP__
106
        /*
107
         * If the load balancing thread is not running, wake it up and
108
         * set CPU-private flag that the kcpulb has been started.
109
         */
15 jermar 110
        if (test_and_set(&CPU->kcpulbstarted) == 0) {
125 jermar 111
            waitq_wakeup(&CPU->kcpulb_wq, 0);
1 jermar 112
            goto loop;
113
        }
114
        #endif /* __SMP__ */
115
 
116
        /*
117
         * For there was nothing to run, the CPU goes to sleep
118
         * until a hardware interrupt or an IPI comes.
119
         * This improves energy saving and hyperthreading.
120
         * On the other hand, several hardware interrupts can be ignored.
121
         */
122
         cpu_sleep();
123
         goto loop;
124
    }
125
 
126
    cpu_priority_high();
114 jermar 127
 
128
    i = 0;
129
retry:
130
    for (; i<RQ_COUNT; i++) {
15 jermar 131
        r = &CPU->rq[i];
1 jermar 132
        spinlock_lock(&r->lock);
133
        if (r->n == 0) {
134
            /*
135
             * If this queue is empty, try a lower-priority queue.
136
             */
137
            spinlock_unlock(&r->lock);
138
            continue;
139
        }
213 jermar 140
 
115 jermar 141
        /* avoid deadlock with relink_rq() */
114 jermar 142
        if (!spinlock_trylock(&CPU->lock)) {
143
            /*
144
             * Unlock r and try again.
145
             */
146
            spinlock_unlock(&r->lock);
147
            goto retry;
148
        }
15 jermar 149
        CPU->nrdy--;
150
        spinlock_unlock(&CPU->lock);
1 jermar 151
 
227 jermar 152
        atomic_dec((int *) &nrdy);
1 jermar 153
        r->n--;
154
 
155
        /*
156
         * Take the first thread from the queue.
157
         */
158
        t = list_get_instance(r->rq_head.next, thread_t, rq_link);
159
        list_remove(&t->rq_link);
160
 
161
        spinlock_unlock(&r->lock);
162
 
163
        spinlock_lock(&t->lock);
15 jermar 164
        t->cpu = CPU;
1 jermar 165
 
166
        t->ticks = us2ticks((i+1)*10000);
167
        t->pri = i; /* eventually correct rq index */
168
 
169
        /*
170
         * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
171
         */
172
        t->flags &= ~X_STOLEN;
173
        spinlock_unlock(&t->lock);
174
 
175
        return t;
176
    }
177
    goto loop;
178
 
179
}
180
 
107 decky 181
 
182
/** Prevent rq starvation
183
 *
184
 * Prevent low priority threads from starving in rq's.
185
 *
186
 * When the function decides to relink rq's, it reconnects
187
 * respective pointers so that in result threads with 'pri'
188
 * greater or equal 'start' are moved to a higher-priority queue.
189
 *
190
 * @param start Threshold priority.
191
 *
1 jermar 192
 */
193
void relink_rq(int start)
194
{
195
    link_t head;
196
    runq_t *r;
197
    int i, n;
198
 
199
    list_initialize(&head);
15 jermar 200
    spinlock_lock(&CPU->lock);
201
    if (CPU->needs_relink > NEEDS_RELINK_MAX) {
1 jermar 202
        for (i = start; i<RQ_COUNT-1; i++) {
203
            /* remember and empty rq[i + 1] */
15 jermar 204
            r = &CPU->rq[i + 1];
1 jermar 205
            spinlock_lock(&r->lock);
206
            list_concat(&head, &r->rq_head);
207
            n = r->n;
208
            r->n = 0;
209
            spinlock_unlock(&r->lock);
210
 
211
            /* append rq[i + 1] to rq[i] */
15 jermar 212
            r = &CPU->rq[i];
1 jermar 213
            spinlock_lock(&r->lock);
214
            list_concat(&r->rq_head, &head);
215
            r->n += n;
216
            spinlock_unlock(&r->lock);
217
        }
15 jermar 218
        CPU->needs_relink = 0;
1 jermar 219
    }
15 jermar 220
    spinlock_unlock(&CPU->lock);               
1 jermar 221
 
222
}
223
 
107 decky 224
 
225
/** The scheduler
226
 *
227
 * The thread scheduling procedure.
228
 *
1 jermar 229
 */
230
void scheduler(void)
231
{
232
    volatile pri_t pri;
233
 
227 jermar 234
    ASSERT(CPU != NULL);
235
 
1 jermar 236
    pri = cpu_priority_high();
237
 
238
    if (haltstate)
239
        halt();
240
 
15 jermar 241
    if (THREAD) {
242
        spinlock_lock(&THREAD->lock);
57 vana 243
        fpu_context_save(&(THREAD->saved_fpu_context));
15 jermar 244
        if (!context_save(&THREAD->saved_context)) {
1 jermar 245
            /*
246
             * This is the place where threads leave scheduler();
247
             */
22 jermar 248
            before_thread_runs();
125 jermar 249
            spinlock_unlock(&THREAD->lock);
15 jermar 250
            cpu_priority_restore(THREAD->saved_context.pri);
1 jermar 251
            return;
252
        }
170 jermar 253
 
254
        /*
255
         * CPU priority of preempted thread is recorded here
256
         * to facilitate scheduler() invocations from
257
         * cpu_priority_high()'ed code (e.g. waitq_sleep_timeout()).
258
         */
15 jermar 259
        THREAD->saved_context.pri = pri;
1 jermar 260
    }
261
 
262
    /*
184 jermar 263
     * Through the 'THE' structure, we keep track of THREAD, TASK, CPU
264
     * and preemption counter. At this point THE could be coming either
265
     * from THREAD's or CPU's stack.
266
     */
267
    the_copy(THE, (the_t *) CPU->stack);
268
 
269
    /*
1 jermar 270
     * We may not keep the old stack.
271
     * Reason: If we kept the old stack and got blocked, for instance, in
272
     * find_best_thread(), the old thread could get rescheduled by another
273
     * CPU and overwrite the part of its own stack that was also used by
274
     * the scheduler on this CPU.
275
     *
276
     * Moreover, we have to bypass the compiler-generated POP sequence
277
     * which is fooled by SP being set to the very top of the stack.
278
     * Therefore the scheduler() function continues in
279
     * scheduler_separated_stack().
280
     */
15 jermar 281
    context_save(&CPU->saved_context);
97 jermar 282
    context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
15 jermar 283
    context_restore(&CPU->saved_context);
1 jermar 284
    /* not reached */
285
}
286
 
107 decky 287
 
288
/** Scheduler stack switch wrapper
289
 *
290
 * Second part of the scheduler() function
291
 * using new stack. Handling the actual context
292
 * switch to a new thread.
293
 *
294
 */
1 jermar 295
void scheduler_separated_stack(void)
296
{
297
    int priority;
298
 
227 jermar 299
    ASSERT(CPU != NULL);
300
 
15 jermar 301
    if (THREAD) {
302
        switch (THREAD->state) {
1 jermar 303
            case Running:
125 jermar 304
            THREAD->state = Ready;
305
            spinlock_unlock(&THREAD->lock);
306
            thread_ready(THREAD);
307
            break;
1 jermar 308
 
309
            case Exiting:
125 jermar 310
            frame_free((__address) THREAD->kstack);
311
            if (THREAD->ustack) {
312
                frame_free((__address) THREAD->ustack);
313
            }
1 jermar 314
 
125 jermar 315
            /*
316
             * Detach from the containing task.
317
             */
318
            spinlock_lock(&TASK->lock);
319
            list_remove(&THREAD->th_link);
320
            spinlock_unlock(&TASK->lock);
73 vana 321
 
125 jermar 322
            spinlock_unlock(&THREAD->lock);
323
 
324
            spinlock_lock(&threads_lock);
325
            list_remove(&THREAD->threads_link);
326
            spinlock_unlock(&threads_lock);
73 vana 327
 
125 jermar 328
            spinlock_lock(&CPU->lock);
329
            if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
330
            spinlock_unlock(&CPU->lock);
331
 
332
            free(THREAD);
333
 
334
            break;
335
 
1 jermar 336
            case Sleeping:
125 jermar 337
            /*
338
             * Prefer the thread after it's woken up.
339
             */
340
            THREAD->pri = -1;
1 jermar 341
 
125 jermar 342
            /*
343
             * We need to release wq->lock which we locked in waitq_sleep().
344
             * Address of wq->lock is kept in THREAD->sleep_queue.
345
             */
346
            spinlock_unlock(&THREAD->sleep_queue->lock);
1 jermar 347
 
125 jermar 348
            /*
349
             * Check for possible requests for out-of-context invocation.
350
             */
351
            if (THREAD->call_me) {
352
                THREAD->call_me(THREAD->call_me_with);
353
                THREAD->call_me = NULL;
354
                THREAD->call_me_with = NULL;
355
            }
1 jermar 356
 
125 jermar 357
            spinlock_unlock(&THREAD->lock);
1 jermar 358
 
125 jermar 359
            break;
360
 
1 jermar 361
            default:
125 jermar 362
            /*
363
             * Entering state is unexpected.
364
             */
365
            panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
366
            break;
1 jermar 367
        }
15 jermar 368
        THREAD = NULL;
1 jermar 369
    }
198 jermar 370
 
214 vana 371
 
15 jermar 372
    THREAD = find_best_thread();
1 jermar 373
 
15 jermar 374
    spinlock_lock(&THREAD->lock);
375
    priority = THREAD->pri;
376
    spinlock_unlock(&THREAD->lock);
192 jermar 377
 
1 jermar 378
    relink_rq(priority);       
379
 
15 jermar 380
    spinlock_lock(&THREAD->lock);  
1 jermar 381
 
382
    /*
383
     * If both the old and the new task are the same, lots of work is avoided.
384
     */
15 jermar 385
    if (TASK != THREAD->task) {
1 jermar 386
        vm_t *m1 = NULL;
387
        vm_t *m2;
388
 
15 jermar 389
        if (TASK) {
390
            spinlock_lock(&TASK->lock);
391
            m1 = TASK->vm;
392
            spinlock_unlock(&TASK->lock);
1 jermar 393
        }
394
 
15 jermar 395
        spinlock_lock(&THREAD->task->lock);
396
        m2 = THREAD->task->vm;
397
        spinlock_unlock(&THREAD->task->lock);
1 jermar 398
 
399
        /*
400
         * Note that it is possible for two tasks to share one vm mapping.
401
         */
402
        if (m1 != m2) {
403
            /*
404
             * Both tasks and vm mappings are different.
405
             * Replace the old one with the new one.
406
             */
407
            vm_install(m2);
408
        }
15 jermar 409
        TASK = THREAD->task;   
1 jermar 410
    }
411
 
15 jermar 412
    THREAD->state = Running;
1 jermar 413
 
414
    #ifdef SCHEDULER_VERBOSE
15 jermar 415
    printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
1 jermar 416
    #endif  
417
 
213 jermar 418
    /*
419
     * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
420
     */
184 jermar 421
    the_copy(THE, (the_t *) THREAD->kstack);
422
 
15 jermar 423
    context_restore(&THREAD->saved_context);
1 jermar 424
    /* not reached */
425
}
426
 
107 decky 427
 
1 jermar 428
#ifdef __SMP__
107 decky 429
/** Load balancing thread
430
 *
431
 * SMP load balancing thread, supervising thread supplies
432
 * for the CPU it's wired to.
433
 *
434
 * @param arg Generic thread argument (unused).
435
 *
1 jermar 436
 */
437
void kcpulb(void *arg)
438
{
439
    thread_t *t;
440
    int count, i, j, k = 0;
441
    pri_t pri;
442
 
443
loop:
444
    /*
445
     * Sleep until there's some work to do.
446
     */
15 jermar 447
    waitq_sleep(&CPU->kcpulb_wq);
1 jermar 448
 
449
not_satisfied:
450
    /*
451
     * Calculate the number of threads that will be migrated/stolen from
452
     * other CPU's. Note that situation can have changed between two
453
     * passes. Each time get the most up to date counts.
454
     */
455
    pri = cpu_priority_high();
15 jermar 456
    spinlock_lock(&CPU->lock);
1 jermar 457
    count = nrdy / config.cpu_active;
15 jermar 458
    count -= CPU->nrdy;
459
    spinlock_unlock(&CPU->lock);
1 jermar 460
    cpu_priority_restore(pri);
461
 
462
    if (count <= 0)
463
        goto satisfied;
464
 
465
    /*
466
     * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
467
     */
468
    for (j=RQ_COUNT-1; j >= 0; j--) {
469
        for (i=0; i < config.cpu_active; i++) {
470
            link_t *l;
471
            runq_t *r;
472
            cpu_t *cpu;
473
 
474
            cpu = &cpus[(i + k) % config.cpu_active];
475
 
476
            /*
477
             * Not interested in ourselves.
478
             * Doesn't require interrupt disabling for kcpulb is X_WIRED.
479
             */
15 jermar 480
            if (CPU == cpu)
115 jermar 481
                continue;              
1 jermar 482
 
483
restart:        pri = cpu_priority_high();
115 jermar 484
            r = &cpu->rq[j];
1 jermar 485
            spinlock_lock(&r->lock);
486
            if (r->n == 0) {
487
                spinlock_unlock(&r->lock);
488
                cpu_priority_restore(pri);
489
                continue;
490
            }
491
 
492
            t = NULL;
493
            l = r->rq_head.prev;    /* search rq from the back */
494
            while (l != &r->rq_head) {
495
                t = list_get_instance(l, thread_t, rq_link);
496
                /*
125 jermar 497
                 * We don't want to steal CPU-wired threads neither threads already stolen.
1 jermar 498
                 * The latter prevents threads from migrating between CPU's without ever being run.
125 jermar 499
                 * We don't want to steal threads whose FPU context is still in CPU.
73 vana 500
                 */
1 jermar 501
                spinlock_lock(&t->lock);
73 vana 502
                if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
115 jermar 503
 
1 jermar 504
                    /*
505
                     * Remove t from r.
506
                     */
507
 
508
                    spinlock_unlock(&t->lock);
509
 
510
                    /*
511
                     * Here we have to avoid deadlock with relink_rq(),
512
                     * because it locks cpu and r in a different order than we do.
513
                     */
514
                    if (!spinlock_trylock(&cpu->lock)) {
515
                        /* Release all locks and try again. */
516
                        spinlock_unlock(&r->lock);
517
                        cpu_priority_restore(pri);
518
                        goto restart;
519
                    }
520
                    cpu->nrdy--;
521
                    spinlock_unlock(&cpu->lock);
522
 
111 palkovsky 523
                    atomic_dec(&nrdy);
1 jermar 524
 
125 jermar 525
                    r->n--;
1 jermar 526
                    list_remove(&t->rq_link);
527
 
528
                    break;
529
                }
530
                spinlock_unlock(&t->lock);
531
                l = l->prev;
532
                t = NULL;
533
            }
534
            spinlock_unlock(&r->lock);
535
 
536
            if (t) {
537
                /*
538
                 * Ready t on local CPU
539
                 */
540
                spinlock_lock(&t->lock);
541
                #ifdef KCPULB_VERBOSE
15 jermar 542
                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 543
                #endif
544
                t->flags |= X_STOLEN;
545
                spinlock_unlock(&t->lock);
546
 
547
                thread_ready(t);
548
 
549
                cpu_priority_restore(pri);
550
 
551
                if (--count == 0)
552
                    goto satisfied;
553
 
554
                /*
125 jermar 555
                 * We are not satisfied yet, focus on another CPU next time.
1 jermar 556
                 */
557
                k++;
558
 
559
                continue;
560
            }
561
            cpu_priority_restore(pri);
562
        }
563
    }
564
 
15 jermar 565
    if (CPU->nrdy) {
1 jermar 566
        /*
567
         * Be a little bit light-weight and let migrated threads run.
568
         */
569
        scheduler();
570
    }
571
    else {
572
        /*
573
         * We failed to migrate a single thread.
574
         * Something more sophisticated should be done.
575
         */
576
        scheduler();
577
    }
578
 
579
    goto not_satisfied;
125 jermar 580
 
1 jermar 581
satisfied:
582
    /*
583
     * Tell find_best_thread() to wake us up later again.
584
     */
15 jermar 585
    CPU->kcpulbstarted = 0;
1 jermar 586
    goto loop;
587
}
588
 
589
#endif /* __SMP__ */