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