kernel/sched_rt.c

   1 /*
   2  * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
   3  * policies)
   4  */
   5
   6 #ifdef CONFIG_SMP
   7
   8 static inline int rt_overloaded(struct rq *rq)
   9 {
  10         return atomic_read(&rq->rd->rto_count);
  11 }
  12
  13 static inline void rt_set_overload(struct rq *rq)
  14 {
  15         cpu_set(rq->cpu, rq->rd->rto_mask);
  16         /*
  17          * Make sure the mask is visible before we set
  18          * the overload count. That is checked to determine
  19          * if we should look at the mask. It would be a shame
  20          * if we looked at the mask, but the mask was not
  21          * updated yet.
  22          */
  23         wmb();
  24         atomic_inc(&rq->rd->rto_count);
  25 }
  26
  27 static inline void rt_clear_overload(struct rq *rq)
  28 {
  29         /* the order here really doesn't matter */
  30         atomic_dec(&rq->rd->rto_count);
  31         cpu_clear(rq->cpu, rq->rd->rto_mask);
  32 }
  33
  34 static void update_rt_migration(struct rq *rq)
  35 {
  36         if (rq->rt.rt_nr_migratory && (rq->rt.rt_nr_running > 1)) {
  37                 if (!rq->rt.overloaded) {
  38                         rt_set_overload(rq);
  39                         rq->rt.overloaded = 1;
  40                 }
  41         } else if (rq->rt.overloaded) {
  42                 rt_clear_overload(rq);
  43                 rq->rt.overloaded = 0;
  44         }
  45 }
  46 #endif /* CONFIG_SMP */
  47
  48 static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
  49 {
  50         return container_of(rt_se, struct task_struct, rt);
  51 }
  52
  53 static inline int on_rt_rq(struct sched_rt_entity *rt_se)
  54 {
  55         return !list_empty(&rt_se->run_list);
  56 }
  57
  58 #ifdef CONFIG_FAIR_GROUP_SCHED
  59
  60 static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
  61 {
  62         if (!rt_rq->tg)
  63                 return SCHED_RT_FRAC;
  64
  65         return rt_rq->tg->rt_ratio;
  66 }
  67
  68 #define for_each_leaf_rt_rq(rt_rq, rq) \
  69         list_for_each_entry(rt_rq, &rq->leaf_rt_rq_list, leaf_rt_rq_list)
  70
  71 static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
  72 {
  73         return rt_rq->rq;
  74 }
  75
  76 static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
  77 {
  78         return rt_se->rt_rq;
  79 }
  80
  81 #define for_each_sched_rt_entity(rt_se) \
  82         for (; rt_se; rt_se = rt_se->parent)
  83
  84 static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
  85 {
  86         return rt_se->my_q;
  87 }
  88
  89 static void enqueue_rt_entity(struct sched_rt_entity *rt_se);
  90 static void dequeue_rt_entity(struct sched_rt_entity *rt_se);
  91
  92 static void sched_rt_ratio_enqueue(struct rt_rq *rt_rq)
  93 {
  94         struct sched_rt_entity *rt_se = rt_rq->rt_se;
  95
  96         if (rt_se && !on_rt_rq(rt_se) && rt_rq->rt_nr_running) {
  97                 struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
  98
  99                 enqueue_rt_entity(rt_se);
 100                 if (rt_rq->highest_prio < curr->prio)
 101                         resched_task(curr);
 102         }
 103 }
 104
 105 static void sched_rt_ratio_dequeue(struct rt_rq *rt_rq)
 106 {
 107         struct sched_rt_entity *rt_se = rt_rq->rt_se;
 108
 109         if (rt_se && on_rt_rq(rt_se))
 110                 dequeue_rt_entity(rt_se);
 111 }
 112
 113 #else
 114
 115 static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
 116 {
 117         return sysctl_sched_rt_ratio;
 118 }
 119
 120 #define for_each_leaf_rt_rq(rt_rq, rq) \
 121         for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
 122
 123 static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
 124 {
 125         return container_of(rt_rq, struct rq, rt);
 126 }
 127
 128 static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
 129 {
 130         struct task_struct *p = rt_task_of(rt_se);
 131         struct rq *rq = task_rq(p);
 132
 133         return &rq->rt;
 134 }
 135
 136 #define for_each_sched_rt_entity(rt_se) \
 137         for (; rt_se; rt_se = NULL)
 138
 139 static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
 140 {
 141         return NULL;
 142 }
 143
 144 static inline void sched_rt_ratio_enqueue(struct rt_rq *rt_rq)
 145 {
 146 }
 147
 148 static inline void sched_rt_ratio_dequeue(struct rt_rq *rt_rq)
 149 {
 150 }
 151
 152 #endif
 153
 154 static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 155 {
 156 #ifdef CONFIG_FAIR_GROUP_SCHED
 157         struct rt_rq *rt_rq = group_rt_rq(rt_se);
 158
 159         if (rt_rq)
 160                 return rt_rq->highest_prio;
 161 #endif
 162
 163         return rt_task_of(rt_se)->prio;
 164 }
 165
 166 static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq)
 167 {
 168         unsigned int rt_ratio = sched_rt_ratio(rt_rq);
 169         u64 period, ratio;
 170
 171         if (rt_ratio == SCHED_RT_FRAC)
 172                 return 0;
 173
 174         if (rt_rq->rt_throttled)
 175                 return 1;
 176
 177         period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
 178         ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
 179
 180         if (rt_rq->rt_time > ratio) {
 181                 struct rq *rq = rq_of_rt_rq(rt_rq);
 182
 183                 rq->rt_throttled = 1;
 184                 rt_rq->rt_throttled = 1;
 185
 186                 sched_rt_ratio_dequeue(rt_rq);
 187                 return 1;
 188         }
 189
 190         return 0;
 191 }
 192
 193 static void update_sched_rt_period(struct rq *rq)
 194 {
 195         struct rt_rq *rt_rq;
 196         u64 period;
 197
 198         while (rq->clock > rq->rt_period_expire) {
 199                 period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
 200                 rq->rt_period_expire += period;
 201
 202                 for_each_leaf_rt_rq(rt_rq, rq) {
 203                         unsigned long rt_ratio = sched_rt_ratio(rt_rq);
 204                         u64 ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
 205
 206                         rt_rq->rt_time -= min(rt_rq->rt_time, ratio);
 207                         if (rt_rq->rt_throttled) {
 208                                 rt_rq->rt_throttled = 0;
 209                                 sched_rt_ratio_enqueue(rt_rq);
 210                         }
 211                 }
 212
 213                 rq->rt_throttled = 0;
 214         }
 215 }
 216
 217 /*
 218  * Update the current task's runtime statistics. Skip current tasks that
 219  * are not in our scheduling class.
 220  */
 221 static void update_curr_rt(struct rq *rq)
 222 {
 223         struct task_struct *curr = rq->curr;
 224         struct sched_rt_entity *rt_se = &curr->rt;
 225         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 226         u64 delta_exec;
 227
 228         if (!task_has_rt_policy(curr))
 229                 return;
 230
 231         delta_exec = rq->clock - curr->se.exec_start;
 232         if (unlikely((s64)delta_exec < 0))
 233                 delta_exec = 0;
 234
 235         schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
 236
 237         curr->se.sum_exec_runtime += delta_exec;
 238         curr->se.exec_start = rq->clock;
 239         cpuacct_charge(curr, delta_exec);
 240
 241         rt_rq->rt_time += delta_exec;
 242         /*
 243          * might make it a tad more accurate:
 244          *
 245          * update_sched_rt_period(rq);
 246          */
 247         if (sched_rt_ratio_exceeded(rt_rq))
 248                 resched_task(curr);
 249 }
 250
 251 static inline
 252 void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 253 {
 254         WARN_ON(!rt_prio(rt_se_prio(rt_se)));
 255         rt_rq->rt_nr_running++;
 256 #if defined CONFIG_SMP || defined CONFIG_FAIR_GROUP_SCHED
 257         if (rt_se_prio(rt_se) < rt_rq->highest_prio)
 258                 rt_rq->highest_prio = rt_se_prio(rt_se);
 259 #endif
 260 #ifdef CONFIG_SMP
 261         if (rt_se->nr_cpus_allowed > 1) {
 262                 struct rq *rq = rq_of_rt_rq(rt_rq);
 263                 rq->rt.rt_nr_migratory++;
 264         }
 265
 266         update_rt_migration(rq_of_rt_rq(rt_rq));
 267 #endif
 268 }
 269
 270 static inline
 271 void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 272 {
 273         WARN_ON(!rt_prio(rt_se_prio(rt_se)));
 274         WARN_ON(!rt_rq->rt_nr_running);
 275         rt_rq->rt_nr_running--;
 276 #if defined CONFIG_SMP || defined CONFIG_FAIR_GROUP_SCHED
 277         if (rt_rq->rt_nr_running) {
 278                 struct rt_prio_array *array;
 279
 280                 WARN_ON(rt_se_prio(rt_se) < rt_rq->highest_prio);
 281                 if (rt_se_prio(rt_se) == rt_rq->highest_prio) {
 282                         /* recalculate */
 283                         array = &rt_rq->active;
 284                         rt_rq->highest_prio =
 285                                 sched_find_first_bit(array->bitmap);
 286                 } /* otherwise leave rq->highest prio alone */
 287         } else
 288                 rt_rq->highest_prio = MAX_RT_PRIO;
 289 #endif
 290 #ifdef CONFIG_SMP
 291         if (rt_se->nr_cpus_allowed > 1) {
 292                 struct rq *rq = rq_of_rt_rq(rt_rq);
 293                 rq->rt.rt_nr_migratory--;
 294         }
 295
 296         update_rt_migration(rq_of_rt_rq(rt_rq));
 297 #endif /* CONFIG_SMP */
 298 }
 299
 300 static void enqueue_rt_entity(struct sched_rt_entity *rt_se)
 301 {
 302         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 303         struct rt_prio_array *array = &rt_rq->active;
 304         struct rt_rq *group_rq = group_rt_rq(rt_se);
 305
 306         if (group_rq && group_rq->rt_throttled)
 307                 return;
 308
 309         list_add_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
 310         __set_bit(rt_se_prio(rt_se), array->bitmap);
 311
 312         inc_rt_tasks(rt_se, rt_rq);
 313 }
 314
 315 static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
 316 {
 317         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 318         struct rt_prio_array *array = &rt_rq->active;
 319
 320         list_del_init(&rt_se->run_list);
 321         if (list_empty(array->queue + rt_se_prio(rt_se)))
 322                 __clear_bit(rt_se_prio(rt_se), array->bitmap);
 323
 324         dec_rt_tasks(rt_se, rt_rq);
 325 }
 326
 327 /*
 328  * Because the prio of an upper entry depends on the lower
 329  * entries, we must remove entries top - down.
 330  *
 331  * XXX: O(1/2 h^2) because we can only walk up, not down the chain.
 332  *      doesn't matter much for now, as h=2 for GROUP_SCHED.
 333  */
 334 static void dequeue_rt_stack(struct task_struct *p)
 335 {
 336         struct sched_rt_entity *rt_se, *top_se;
 337
 338         /*
 339          * dequeue all, top - down.
 340          */
 341         do {
 342                 rt_se = &p->rt;
 343                 top_se = NULL;
 344                 for_each_sched_rt_entity(rt_se) {
 345                         if (on_rt_rq(rt_se))
 346                                 top_se = rt_se;
 347                 }
 348                 if (top_se)
 349                         dequeue_rt_entity(top_se);
 350         } while (top_se);
 351 }
 352
 353 /*
 354  * Adding/removing a task to/from a priority array:
 355  */
 356 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
 357 {
 358         struct sched_rt_entity *rt_se = &p->rt;
 359
 360         if (wakeup)
 361                 rt_se->timeout = 0;
 362
 363         dequeue_rt_stack(p);
 364
 365         /*
 366          * enqueue everybody, bottom - up.
 367          */
 368         for_each_sched_rt_entity(rt_se)
 369                 enqueue_rt_entity(rt_se);
 370
 371         inc_cpu_load(rq, p->se.load.weight);
 372 }
 373
 374 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
 375 {
 376         struct sched_rt_entity *rt_se = &p->rt;
 377         struct rt_rq *rt_rq;
 378
 379         update_curr_rt(rq);
 380
 381         dequeue_rt_stack(p);
 382
 383         /*
 384          * re-enqueue all non-empty rt_rq entities.
 385          */
 386         for_each_sched_rt_entity(rt_se) {
 387                 rt_rq = group_rt_rq(rt_se);
 388                 if (rt_rq && rt_rq->rt_nr_running)
 389                         enqueue_rt_entity(rt_se);
 390         }
 391
 392         dec_cpu_load(rq, p->se.load.weight);
 393 }
 394
 395 /*
 396  * Put task to the end of the run list without the overhead of dequeue
 397  * followed by enqueue.
 398  */
 399 static
 400 void requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
 401 {
 402         struct rt_prio_array *array = &rt_rq->active;
 403
 404         list_move_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
 405 }
 406
 407 static void requeue_task_rt(struct rq *rq, struct task_struct *p)
 408 {
 409         struct sched_rt_entity *rt_se = &p->rt;
 410         struct rt_rq *rt_rq;
 411
 412         for_each_sched_rt_entity(rt_se) {
 413                 rt_rq = rt_rq_of_se(rt_se);
 414                 requeue_rt_entity(rt_rq, rt_se);
 415         }
 416 }
 417
 418 static void yield_task_rt(struct rq *rq)
 419 {
 420         requeue_task_rt(rq, rq->curr);
 421 }
 422
 423 #ifdef CONFIG_SMP
 424 static int find_lowest_rq(struct task_struct *task);
 425
 426 static int select_task_rq_rt(struct task_struct *p, int sync)
 427 {
 428         struct rq *rq = task_rq(p);
 429
 430         /*
 431          * If the current task is an RT task, then
 432          * try to see if we can wake this RT task up on another
 433          * runqueue. Otherwise simply start this RT task
 434          * on its current runqueue.
 435          *
 436          * We want to avoid overloading runqueues. Even if
 437          * the RT task is of higher priority than the current RT task.
 438          * RT tasks behave differently than other tasks. If
 439          * one gets preempted, we try to push it off to another queue.
 440          * So trying to keep a preempting RT task on the same
 441          * cache hot CPU will force the running RT task to
 442          * a cold CPU. So we waste all the cache for the lower
 443          * RT task in hopes of saving some of a RT task
 444          * that is just being woken and probably will have
 445          * cold cache anyway.
 446          */
 447         if (unlikely(rt_task(rq->curr)) &&
 448             (p->rt.nr_cpus_allowed > 1)) {
 449                 int cpu = find_lowest_rq(p);
 450
 451                 return (cpu == -1) ? task_cpu(p) : cpu;
 452         }
 453
 454         /*
 455          * Otherwise, just let it ride on the affined RQ and the
 456          * post-schedule router will push the preempted task away
 457          */
 458         return task_cpu(p);
 459 }
 460 #endif /* CONFIG_SMP */
 461
 462 /*
 463  * Preempt the current task with a newly woken task if needed:
 464  */
 465 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
 466 {
 467         if (p->prio < rq->curr->prio)
 468                 resched_task(rq->curr);
 469 }
 470
 471 static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
 472                                                    struct rt_rq *rt_rq)
 473 {
 474         struct rt_prio_array *array = &rt_rq->active;
 475         struct sched_rt_entity *next = NULL;
 476         struct list_head *queue;
 477         int idx;
 478
 479         idx = sched_find_first_bit(array->bitmap);
 480         BUG_ON(idx >= MAX_RT_PRIO);
 481
 482         queue = array->queue + idx;
 483         next = list_entry(queue->next, struct sched_rt_entity, run_list);
 484
 485         return next;
 486 }
 487
 488 static struct task_struct *pick_next_task_rt(struct rq *rq)
 489 {
 490         struct sched_rt_entity *rt_se;
 491         struct task_struct *p;
 492         struct rt_rq *rt_rq;
 493
 494         rt_rq = &rq->rt;
 495
 496         if (unlikely(!rt_rq->rt_nr_running))
 497                 return NULL;
 498
 499         if (sched_rt_ratio_exceeded(rt_rq))
 500                 return NULL;
 501
 502         do {
 503                 rt_se = pick_next_rt_entity(rq, rt_rq);
 504                 BUG_ON(!rt_se);
 505                 rt_rq = group_rt_rq(rt_se);
 506         } while (rt_rq);
 507
 508         p = rt_task_of(rt_se);
 509         p->se.exec_start = rq->clock;
 510         return p;
 511 }
 512
 513 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 514 {
 515         update_curr_rt(rq);
 516         p->se.exec_start = 0;
 517 }
 518
 519 #ifdef CONFIG_SMP
 520
 521 /* Only try algorithms three times */
 522 #define RT_MAX_TRIES 3
 523
 524 static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
 525 static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
 526
 527 static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
 528 {
 529         if (!task_running(rq, p) &&
 530             (cpu < 0 || cpu_isset(cpu, p->cpus_allowed)) &&
 531             (p->rt.nr_cpus_allowed > 1))
 532                 return 1;
 533         return 0;
 534 }
 535
 536 /* Return the second highest RT task, NULL otherwise */
 537 static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu)
 538 {
 539         struct task_struct *next = NULL;
 540         struct sched_rt_entity *rt_se;
 541         struct rt_prio_array *array;
 542         struct rt_rq *rt_rq;
 543         int idx;
 544
 545         for_each_leaf_rt_rq(rt_rq, rq) {
 546                 array = &rt_rq->active;
 547                 idx = sched_find_first_bit(array->bitmap);
 548  next_idx:
 549                 if (idx >= MAX_RT_PRIO)
 550                         continue;
 551                 if (next && next->prio < idx)
 552                         continue;
 553                 list_for_each_entry(rt_se, array->queue + idx, run_list) {
 554                         struct task_struct *p = rt_task_of(rt_se);
 555                         if (pick_rt_task(rq, p, cpu)) {
 556                                 next = p;
 557                                 break;
 558                         }
 559                 }
 560                 if (!next) {
 561                         idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
 562                         goto next_idx;
 563                 }
 564         }
 565
 566         return next;
 567 }
 568
 569 static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
 570
 571 static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
 572 {
 573         int       lowest_prio = -1;
 574         int       lowest_cpu  = -1;
 575         int       count       = 0;
 576         int       cpu;
 577
 578         cpus_and(*lowest_mask, task_rq(task)->rd->online, task->cpus_allowed);
 579
 580         /*
 581          * Scan each rq for the lowest prio.
 582          */
 583         for_each_cpu_mask(cpu, *lowest_mask) {
 584                 struct rq *rq = cpu_rq(cpu);
 585
 586                 /* We look for lowest RT prio or non-rt CPU */
 587                 if (rq->rt.highest_prio >= MAX_RT_PRIO) {
 588                         /*
 589                          * if we already found a low RT queue
 590                          * and now we found this non-rt queue
 591                          * clear the mask and set our bit.
 592                          * Otherwise just return the queue as is
 593                          * and the count==1 will cause the algorithm
 594                          * to use the first bit found.
 595                          */
 596                         if (lowest_cpu != -1) {
 597                                 cpus_clear(*lowest_mask);
 598                                 cpu_set(rq->cpu, *lowest_mask);
 599                         }
 600                         return 1;
 601                 }
 602
 603                 /* no locking for now */
 604                 if ((rq->rt.highest_prio > task->prio)
 605                     && (rq->rt.highest_prio >= lowest_prio)) {
 606                         if (rq->rt.highest_prio > lowest_prio) {
 607                                 /* new low - clear old data */
 608                                 lowest_prio = rq->rt.highest_prio;
 609                                 lowest_cpu = cpu;
 610                                 count = 0;
 611                         }
 612                         count++;
 613                 } else
 614                         cpu_clear(cpu, *lowest_mask);
 615         }
 616
 617         /*
 618          * Clear out all the set bits that represent
 619          * runqueues that were of higher prio than
 620          * the lowest_prio.
 621          */
 622         if (lowest_cpu > 0) {
 623                 /*
 624                  * Perhaps we could add another cpumask op to
 625                  * zero out bits. Like cpu_zero_bits(cpumask, nrbits);
 626                  * Then that could be optimized to use memset and such.
 627                  */
 628                 for_each_cpu_mask(cpu, *lowest_mask) {
 629                         if (cpu >= lowest_cpu)
 630                                 break;
 631                         cpu_clear(cpu, *lowest_mask);
 632                 }
 633         }
 634
 635         return count;
 636 }
 637
 638 static inline int pick_optimal_cpu(int this_cpu, cpumask_t *mask)
 639 {
 640         int first;
 641
 642         /* "this_cpu" is cheaper to preempt than a remote processor */
 643         if ((this_cpu != -1) && cpu_isset(this_cpu, *mask))
 644                 return this_cpu;
 645
 646         first = first_cpu(*mask);
 647         if (first != NR_CPUS)
 648                 return first;
 649
 650         return -1;
 651 }
 652
 653 static int find_lowest_rq(struct task_struct *task)
 654 {
 655         struct sched_domain *sd;
 656         cpumask_t *lowest_mask = &__get_cpu_var(local_cpu_mask);
 657         int this_cpu = smp_processor_id();
 658         int cpu      = task_cpu(task);
 659         int count    = find_lowest_cpus(task, lowest_mask);
 660
 661         if (!count)
 662                 return -1; /* No targets found */
 663
 664         /*
 665          * There is no sense in performing an optimal search if only one
 666          * target is found.
 667          */
 668         if (count == 1)
 669                 return first_cpu(*lowest_mask);
 670
 671         /*
 672          * At this point we have built a mask of cpus representing the
 673          * lowest priority tasks in the system.  Now we want to elect
 674          * the best one based on our affinity and topology.
 675          *
 676          * We prioritize the last cpu that the task executed on since
 677          * it is most likely cache-hot in that location.
 678          */
 679         if (cpu_isset(cpu, *lowest_mask))
 680                 return cpu;
 681
 682         /*
 683          * Otherwise, we consult the sched_domains span maps to figure
 684          * out which cpu is logically closest to our hot cache data.
 685          */
 686         if (this_cpu == cpu)
 687                 this_cpu = -1; /* Skip this_cpu opt if the same */
 688
 689         for_each_domain(cpu, sd) {
 690                 if (sd->flags & SD_WAKE_AFFINE) {
 691                         cpumask_t domain_mask;
 692                         int       best_cpu;
 693
 694                         cpus_and(domain_mask, sd->span, *lowest_mask);
 695
 696                         best_cpu = pick_optimal_cpu(this_cpu,
 697                                                     &domain_mask);
 698                         if (best_cpu != -1)
 699                                 return best_cpu;
 700                 }
 701         }
 702
 703         /*
 704          * And finally, if there were no matches within the domains
 705          * just give the caller *something* to work with from the compatible
 706          * locations.
 707          */
 708         return pick_optimal_cpu(this_cpu, lowest_mask);
 709 }
 710
 711 /* Will lock the rq it finds */
 712 static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
 713 {
 714         struct rq *lowest_rq = NULL;
 715         int tries;
 716         int cpu;
 717
 718         for (tries = 0; tries < RT_MAX_TRIES; tries++) {
 719                 cpu = find_lowest_rq(task);
 720
 721                 if ((cpu == -1) || (cpu == rq->cpu))
 722                         break;
 723
 724                 lowest_rq = cpu_rq(cpu);
 725
 726                 /* if the prio of this runqueue changed, try again */
 727                 if (double_lock_balance(rq, lowest_rq)) {
 728                         /*
 729                          * We had to unlock the run queue. In
 730                          * the mean time, task could have
 731                          * migrated already or had its affinity changed.
 732                          * Also make sure that it wasn't scheduled on its rq.
 733                          */
 734                         if (unlikely(task_rq(task) != rq ||
 735                                      !cpu_isset(lowest_rq->cpu,
 736                                                 task->cpus_allowed) ||
 737                                      task_running(rq, task) ||
 738                                      !task->se.on_rq)) {
 739
 740                                 spin_unlock(&lowest_rq->lock);
 741                                 lowest_rq = NULL;
 742                                 break;
 743                         }
 744                 }
 745
 746                 /* If this rq is still suitable use it. */
 747                 if (lowest_rq->rt.highest_prio > task->prio)
 748                         break;
 749
 750                 /* try again */
 751                 spin_unlock(&lowest_rq->lock);
 752                 lowest_rq = NULL;
 753         }
 754
 755         return lowest_rq;
 756 }
 757
 758 /*
 759  * If the current CPU has more than one RT task, see if the non
 760  * running task can migrate over to a CPU that is running a task
 761  * of lesser priority.
 762  */
 763 static int push_rt_task(struct rq *rq)
 764 {
 765         struct task_struct *next_task;
 766         struct rq *lowest_rq;
 767         int ret = 0;
 768         int paranoid = RT_MAX_TRIES;
 769
 770         if (!rq->rt.overloaded)
 771                 return 0;
 772
 773         next_task = pick_next_highest_task_rt(rq, -1);
 774         if (!next_task)
 775                 return 0;
 776
 777  retry:
 778         if (unlikely(next_task == rq->curr)) {
 779                 WARN_ON(1);
 780                 return 0;
 781         }
 782
 783         /*
 784          * It's possible that the next_task slipped in of
 785          * higher priority than current. If that's the case
 786          * just reschedule current.
 787          */
 788         if (unlikely(next_task->prio < rq->curr->prio)) {
 789                 resched_task(rq->curr);
 790                 return 0;
 791         }
 792
 793         /* We might release rq lock */
 794         get_task_struct(next_task);
 795
 796         /* find_lock_lowest_rq locks the rq if found */
 797         lowest_rq = find_lock_lowest_rq(next_task, rq);
 798         if (!lowest_rq) {
 799                 struct task_struct *task;
 800                 /*
 801                  * find lock_lowest_rq releases rq->lock
 802                  * so it is possible that next_task has changed.
 803                  * If it has, then try again.
 804                  */
 805                 task = pick_next_highest_task_rt(rq, -1);
 806                 if (unlikely(task != next_task) && task && paranoid--) {
 807                         put_task_struct(next_task);
 808                         next_task = task;
 809                         goto retry;
 810                 }
 811                 goto out;
 812         }
 813
 814         deactivate_task(rq, next_task, 0);
 815         set_task_cpu(next_task, lowest_rq->cpu);
 816         activate_task(lowest_rq, next_task, 0);
 817
 818         resched_task(lowest_rq->curr);
 819
 820         spin_unlock(&lowest_rq->lock);
 821
 822         ret = 1;
 823 out:
 824         put_task_struct(next_task);
 825
 826         return ret;
 827 }
 828
 829 /*
 830  * TODO: Currently we just use the second highest prio task on
 831  *       the queue, and stop when it can't migrate (or there's
 832  *       no more RT tasks).  There may be a case where a lower
 833  *       priority RT task has a different affinity than the
 834  *       higher RT task. In this case the lower RT task could
 835  *       possibly be able to migrate where as the higher priority
 836  *       RT task could not.  We currently ignore this issue.
 837  *       Enhancements are welcome!
 838  */
 839 static void push_rt_tasks(struct rq *rq)
 840 {
 841         /* push_rt_task will return true if it moved an RT */
 842         while (push_rt_task(rq))
 843                 ;
 844 }
 845
 846 static int pull_rt_task(struct rq *this_rq)
 847 {
 848         int this_cpu = this_rq->cpu, ret = 0, cpu;
 849         struct task_struct *p, *next;
 850         struct rq *src_rq;
 851
 852         if (likely(!rt_overloaded(this_rq)))
 853                 return 0;
 854
 855         next = pick_next_task_rt(this_rq);
 856
 857         for_each_cpu_mask(cpu, this_rq->rd->rto_mask) {
 858                 if (this_cpu == cpu)
 859                         continue;
 860
 861                 src_rq = cpu_rq(cpu);
 862                 /*
 863                  * We can potentially drop this_rq's lock in
 864                  * double_lock_balance, and another CPU could
 865                  * steal our next task - hence we must cause
 866                  * the caller to recalculate the next task
 867                  * in that case:
 868                  */
 869                 if (double_lock_balance(this_rq, src_rq)) {
 870                         struct task_struct *old_next = next;
 871
 872                         next = pick_next_task_rt(this_rq);
 873                         if (next != old_next)
 874                                 ret = 1;
 875                 }
 876
 877                 /*
 878                  * Are there still pullable RT tasks?
 879                  */
 880                 if (src_rq->rt.rt_nr_running <= 1)
 881                         goto skip;
 882
 883                 p = pick_next_highest_task_rt(src_rq, this_cpu);
 884
 885                 /*
 886                  * Do we have an RT task that preempts
 887                  * the to-be-scheduled task?
 888                  */
 889                 if (p && (!next || (p->prio < next->prio))) {
 890                         WARN_ON(p == src_rq->curr);
 891                         WARN_ON(!p->se.on_rq);
 892
 893                         /*
 894                          * There's a chance that p is higher in priority
 895                          * than what's currently running on its cpu.
 896                          * This is just that p is wakeing up and hasn't
 897                          * had a chance to schedule. We only pull
 898                          * p if it is lower in priority than the
 899                          * current task on the run queue or
 900                          * this_rq next task is lower in prio than
 901                          * the current task on that rq.
 902                          */
 903                         if (p->prio < src_rq->curr->prio ||
 904                             (next && next->prio < src_rq->curr->prio))
 905                                 goto skip;
 906
 907                         ret = 1;
 908
 909                         deactivate_task(src_rq, p, 0);
 910                         set_task_cpu(p, this_cpu);
 911                         activate_task(this_rq, p, 0);
 912                         /*
 913                          * We continue with the search, just in
 914                          * case there's an even higher prio task
 915                          * in another runqueue. (low likelyhood
 916                          * but possible)
 917                          *
 918                          * Update next so that we won't pick a task
 919                          * on another cpu with a priority lower (or equal)
 920                          * than the one we just picked.
 921                          */
 922                         next = p;
 923
 924                 }
 925  skip:
 926                 spin_unlock(&src_rq->lock);
 927         }
 928
 929         return ret;
 930 }
 931
 932 static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
 933 {
 934         /* Try to pull RT tasks here if we lower this rq's prio */
 935         if (unlikely(rt_task(prev)) && rq->rt.highest_prio > prev->prio)
 936                 pull_rt_task(rq);
 937 }
 938
 939 static void post_schedule_rt(struct rq *rq)
 940 {
 941         /*
 942          * If we have more than one rt_task queued, then
 943          * see if we can push the other rt_tasks off to other CPUS.
 944          * Note we may release the rq lock, and since
 945          * the lock was owned by prev, we need to release it
 946          * first via finish_lock_switch and then reaquire it here.
 947          */
 948         if (unlikely(rq->rt.overloaded)) {
 949                 spin_lock_irq(&rq->lock);
 950                 push_rt_tasks(rq);
 951                 spin_unlock_irq(&rq->lock);
 952         }
 953 }
 954
 955
 956 static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
 957 {
 958         if (!task_running(rq, p) &&
 959             (p->prio >= rq->rt.highest_prio) &&
 960             rq->rt.overloaded)
 961                 push_rt_tasks(rq);
 962 }
 963
 964 static unsigned long
 965 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 966                 unsigned long max_load_move,
 967                 struct sched_domain *sd, enum cpu_idle_type idle,
 968                 int *all_pinned, int *this_best_prio)
 969 {
 970         /* don't touch RT tasks */
 971         return 0;
 972 }
 973
 974 static int
 975 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 976                  struct sched_domain *sd, enum cpu_idle_type idle)
 977 {
 978         /* don't touch RT tasks */
 979         return 0;
 980 }
 981
 982 static void set_cpus_allowed_rt(struct task_struct *p, cpumask_t *new_mask)
 983 {
 984         int weight = cpus_weight(*new_mask);
 985
 986         BUG_ON(!rt_task(p));
 987
 988         /*
 989          * Update the migration status of the RQ if we have an RT task
 990          * which is running AND changing its weight value.
 991          */
 992         if (p->se.on_rq && (weight != p->rt.nr_cpus_allowed)) {
 993                 struct rq *rq = task_rq(p);
 994
 995                 if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) {
 996                         rq->rt.rt_nr_migratory++;
 997                 } else if ((p->rt.nr_cpus_allowed > 1) && (weight <= 1)) {
 998                         BUG_ON(!rq->rt.rt_nr_migratory);
 999                         rq->rt.rt_nr_migratory--;
1000                 }
1001
1002                 update_rt_migration(rq);
1003         }
1004
1005         p->cpus_allowed    = *new_mask;
1006         p->rt.nr_cpus_allowed = weight;
1007 }
1008
1009 /* Assumes rq->lock is held */
1010 static void join_domain_rt(struct rq *rq)
1011 {
1012         if (rq->rt.overloaded)
1013                 rt_set_overload(rq);
1014 }
1015
1016 /* Assumes rq->lock is held */
1017 static void leave_domain_rt(struct rq *rq)
1018 {
1019         if (rq->rt.overloaded)
1020                 rt_clear_overload(rq);
1021 }
1022
1023 /*
1024  * When switch from the rt queue, we bring ourselves to a position
1025  * that we might want to pull RT tasks from other runqueues.
1026  */
1027 static void switched_from_rt(struct rq *rq, struct task_struct *p,
1028                            int running)
1029 {
1030         /*
1031          * If there are other RT tasks then we will reschedule
1032          * and the scheduling of the other RT tasks will handle
1033          * the balancing. But if we are the last RT task
1034          * we may need to handle the pulling of RT tasks
1035          * now.
1036          */
1037         if (!rq->rt.rt_nr_running)
1038                 pull_rt_task(rq);
1039 }
1040 #endif /* CONFIG_SMP */
1041
1042 /*
1043  * When switching a task to RT, we may overload the runqueue
1044  * with RT tasks. In this case we try to push them off to
1045  * other runqueues.
1046  */
1047 static void switched_to_rt(struct rq *rq, struct task_struct *p,
1048                            int running)
1049 {
1050         int check_resched = 1;
1051
1052         /*
1053          * If we are already running, then there's nothing
1054          * that needs to be done. But if we are not running
1055          * we may need to preempt the current running task.
1056          * If that current running task is also an RT task
1057          * then see if we can move to another run queue.
1058          */
1059         if (!running) {
1060 #ifdef CONFIG_SMP
1061                 if (rq->rt.overloaded && push_rt_task(rq) &&
1062                     /* Don't resched if we changed runqueues */
1063                     rq != task_rq(p))
1064                         check_resched = 0;
1065 #endif /* CONFIG_SMP */
1066                 if (check_resched && p->prio < rq->curr->prio)
1067                         resched_task(rq->curr);
1068         }
1069 }
1070
1071 /*
1072  * Priority of the task has changed. This may cause
1073  * us to initiate a push or pull.
1074  */
1075 static void prio_changed_rt(struct rq *rq, struct task_struct *p,
1076                             int oldprio, int running)
1077 {
1078         if (running) {
1079 #ifdef CONFIG_SMP
1080                 /*
1081                  * If our priority decreases while running, we
1082                  * may need to pull tasks to this runqueue.
1083                  */
1084                 if (oldprio < p->prio)
1085                         pull_rt_task(rq);
1086                 /*
1087                  * If there's a higher priority task waiting to run
1088                  * then reschedule.
1089                  */
1090                 if (p->prio > rq->rt.highest_prio)
1091                         resched_task(p);
1092 #else
1093                 /* For UP simply resched on drop of prio */
1094                 if (oldprio < p->prio)
1095                         resched_task(p);
1096 #endif /* CONFIG_SMP */
1097         } else {
1098                 /*
1099                  * This task is not running, but if it is
1100                  * greater than the current running task
1101                  * then reschedule.
1102                  */
1103                 if (p->prio < rq->curr->prio)
1104                         resched_task(rq->curr);
1105         }
1106 }
1107
1108 static void watchdog(struct rq *rq, struct task_struct *p)
1109 {
1110         unsigned long soft, hard;
1111
1112         if (!p->signal)
1113                 return;
1114
1115         soft = p->signal->rlim[RLIMIT_RTTIME].rlim_cur;
1116         hard = p->signal->rlim[RLIMIT_RTTIME].rlim_max;
1117
1118         if (soft != RLIM_INFINITY) {
1119                 unsigned long next;
1120
1121                 p->rt.timeout++;
1122                 next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
1123                 if (p->rt.timeout > next)
1124                         p->it_sched_expires = p->se.sum_exec_runtime;
1125         }
1126 }
1127
1128 static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
1129 {
1130         update_curr_rt(rq);
1131
1132         watchdog(rq, p);
1133
1134         /*
1135          * RR tasks need a special form of timeslice management.
1136          * FIFO tasks have no timeslices.
1137          */
1138         if (p->policy != SCHED_RR)
1139                 return;
1140
1141         if (--p->rt.time_slice)
1142                 return;
1143
1144         p->rt.time_slice = DEF_TIMESLICE;
1145
1146         /*
1147          * Requeue to the end of queue if we are not the only element
1148          * on the queue:
1149          */
1150         if (p->rt.run_list.prev != p->rt.run_list.next) {
1151                 requeue_task_rt(rq, p);
1152                 set_tsk_need_resched(p);
1153         }
1154 }
1155
1156 static void set_curr_task_rt(struct rq *rq)
1157 {
1158         struct task_struct *p = rq->curr;
1159
1160         p->se.exec_start = rq->clock;
1161 }
1162
1163 const struct sched_class rt_sched_class = {
1164         .next                   = &fair_sched_class,
1165         .enqueue_task           = enqueue_task_rt,
1166         .dequeue_task           = dequeue_task_rt,
1167         .yield_task             = yield_task_rt,
1168 #ifdef CONFIG_SMP
1169         .select_task_rq         = select_task_rq_rt,
1170 #endif /* CONFIG_SMP */
1171
1172         .check_preempt_curr     = check_preempt_curr_rt,
1173
1174         .pick_next_task         = pick_next_task_rt,
1175         .put_prev_task          = put_prev_task_rt,
1176
1177 #ifdef CONFIG_SMP
1178         .load_balance           = load_balance_rt,
1179         .move_one_task          = move_one_task_rt,
1180         .set_cpus_allowed       = set_cpus_allowed_rt,
1181         .join_domain            = join_domain_rt,
1182         .leave_domain           = leave_domain_rt,
1183         .pre_schedule           = pre_schedule_rt,
1184         .post_schedule          = post_schedule_rt,
1185         .task_wake_up           = task_wake_up_rt,
1186         .switched_from          = switched_from_rt,
1187 #endif
1188
1189         .set_curr_task          = set_curr_task_rt,
1190         .task_tick              = task_tick_rt,
1191
1192         .prio_changed           = prio_changed_rt,
1193         .switched_to            = switched_to_rt,
1194 };