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 static inline int rt_rq_throttled(struct rt_rq *rt_rq)
 114 {
 115         return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
 116 }
 117
 118 static int rt_se_boosted(struct sched_rt_entity *rt_se)
 119 {
 120         struct rt_rq *rt_rq = group_rt_rq(rt_se);
 121         struct task_struct *p;
 122
 123         if (rt_rq)
 124                 return !!rt_rq->rt_nr_boosted;
 125
 126         p = rt_task_of(rt_se);
 127         return p->prio != p->normal_prio;
 128 }
 129
 130 #else
 131
 132 static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
 133 {
 134         return sysctl_sched_rt_ratio;
 135 }
 136
 137 #define for_each_leaf_rt_rq(rt_rq, rq) \
 138         for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
 139
 140 static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
 141 {
 142         return container_of(rt_rq, struct rq, rt);
 143 }
 144
 145 static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
 146 {
 147         struct task_struct *p = rt_task_of(rt_se);
 148         struct rq *rq = task_rq(p);
 149
 150         return &rq->rt;
 151 }
 152
 153 #define for_each_sched_rt_entity(rt_se) \
 154         for (; rt_se; rt_se = NULL)
 155
 156 static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
 157 {
 158         return NULL;
 159 }
 160
 161 static inline void sched_rt_ratio_enqueue(struct rt_rq *rt_rq)
 162 {
 163 }
 164
 165 static inline void sched_rt_ratio_dequeue(struct rt_rq *rt_rq)
 166 {
 167 }
 168
 169 static inline int rt_rq_throttled(struct rt_rq *rt_rq)
 170 {
 171         return rt_rq->rt_throttled;
 172 }
 173 #endif
 174
 175 static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 176 {
 177 #ifdef CONFIG_FAIR_GROUP_SCHED
 178         struct rt_rq *rt_rq = group_rt_rq(rt_se);
 179
 180         if (rt_rq)
 181                 return rt_rq->highest_prio;
 182 #endif
 183
 184         return rt_task_of(rt_se)->prio;
 185 }
 186
 187 static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq)
 188 {
 189         unsigned int rt_ratio = sched_rt_ratio(rt_rq);
 190         u64 period, ratio;
 191
 192         if (rt_ratio == SCHED_RT_FRAC)
 193                 return 0;
 194
 195         if (rt_rq->rt_throttled)
 196                 return rt_rq_throttled(rt_rq);
 197
 198         period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
 199         ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
 200
 201         if (rt_rq->rt_time > ratio) {
 202                 struct rq *rq = rq_of_rt_rq(rt_rq);
 203
 204                 rq->rt_throttled = 1;
 205                 rt_rq->rt_throttled = 1;
 206
 207                 if (rt_rq_throttled(rt_rq)) {
 208                         sched_rt_ratio_dequeue(rt_rq);
 209                         return 1;
 210                 }
 211         }
 212
 213         return 0;
 214 }
 215
 216 static void update_sched_rt_period(struct rq *rq)
 217 {
 218         struct rt_rq *rt_rq;
 219         u64 period;
 220
 221         while (rq->clock > rq->rt_period_expire) {
 222                 period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
 223                 rq->rt_period_expire += period;
 224
 225                 for_each_leaf_rt_rq(rt_rq, rq) {
 226                         unsigned long rt_ratio = sched_rt_ratio(rt_rq);
 227                         u64 ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
 228
 229                         rt_rq->rt_time -= min(rt_rq->rt_time, ratio);
 230                         if (rt_rq->rt_throttled) {
 231                                 rt_rq->rt_throttled = 0;
 232                                 sched_rt_ratio_enqueue(rt_rq);
 233                         }
 234                 }
 235
 236                 rq->rt_throttled = 0;
 237         }
 238 }
 239
 240 /*
 241  * Update the current task's runtime statistics. Skip current tasks that
 242  * are not in our scheduling class.
 243  */
 244 static void update_curr_rt(struct rq *rq)
 245 {
 246         struct task_struct *curr = rq->curr;
 247         struct sched_rt_entity *rt_se = &curr->rt;
 248         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 249         u64 delta_exec;
 250
 251         if (!task_has_rt_policy(curr))
 252                 return;
 253
 254         delta_exec = rq->clock - curr->se.exec_start;
 255         if (unlikely((s64)delta_exec < 0))
 256                 delta_exec = 0;
 257
 258         schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
 259
 260         curr->se.sum_exec_runtime += delta_exec;
 261         curr->se.exec_start = rq->clock;
 262         cpuacct_charge(curr, delta_exec);
 263
 264         rt_rq->rt_time += delta_exec;
 265         /*
 266          * might make it a tad more accurate:
 267          *
 268          * update_sched_rt_period(rq);
 269          */
 270         if (sched_rt_ratio_exceeded(rt_rq))
 271                 resched_task(curr);
 272 }
 273
 274 static inline
 275 void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 276 {
 277         WARN_ON(!rt_prio(rt_se_prio(rt_se)));
 278         rt_rq->rt_nr_running++;
 279 #if defined CONFIG_SMP || defined CONFIG_FAIR_GROUP_SCHED
 280         if (rt_se_prio(rt_se) < rt_rq->highest_prio)
 281                 rt_rq->highest_prio = rt_se_prio(rt_se);
 282 #endif
 283 #ifdef CONFIG_SMP
 284         if (rt_se->nr_cpus_allowed > 1) {
 285                 struct rq *rq = rq_of_rt_rq(rt_rq);
 286                 rq->rt.rt_nr_migratory++;
 287         }
 288
 289         update_rt_migration(rq_of_rt_rq(rt_rq));
 290 #endif
 291 #ifdef CONFIG_FAIR_GROUP_SCHED
 292         if (rt_se_boosted(rt_se))
 293                 rt_rq->rt_nr_boosted++;
 294 #endif
 295 }
 296
 297 static inline
 298 void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 299 {
 300         WARN_ON(!rt_prio(rt_se_prio(rt_se)));
 301         WARN_ON(!rt_rq->rt_nr_running);
 302         rt_rq->rt_nr_running--;
 303 #if defined CONFIG_SMP || defined CONFIG_FAIR_GROUP_SCHED
 304         if (rt_rq->rt_nr_running) {
 305                 struct rt_prio_array *array;
 306
 307                 WARN_ON(rt_se_prio(rt_se) < rt_rq->highest_prio);
 308                 if (rt_se_prio(rt_se) == rt_rq->highest_prio) {
 309                         /* recalculate */
 310                         array = &rt_rq->active;
 311                         rt_rq->highest_prio =
 312                                 sched_find_first_bit(array->bitmap);
 313                 } /* otherwise leave rq->highest prio alone */
 314         } else
 315                 rt_rq->highest_prio = MAX_RT_PRIO;
 316 #endif
 317 #ifdef CONFIG_SMP
 318         if (rt_se->nr_cpus_allowed > 1) {
 319                 struct rq *rq = rq_of_rt_rq(rt_rq);
 320                 rq->rt.rt_nr_migratory--;
 321         }
 322
 323         update_rt_migration(rq_of_rt_rq(rt_rq));
 324 #endif /* CONFIG_SMP */
 325 #ifdef CONFIG_FAIR_GROUP_SCHED
 326         if (rt_se_boosted(rt_se))
 327                 rt_rq->rt_nr_boosted--;
 328
 329         WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);
 330 #endif
 331 }
 332
 333 static void enqueue_rt_entity(struct sched_rt_entity *rt_se)
 334 {
 335         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 336         struct rt_prio_array *array = &rt_rq->active;
 337         struct rt_rq *group_rq = group_rt_rq(rt_se);
 338
 339         if (group_rq && rt_rq_throttled(group_rq))
 340                 return;
 341
 342         list_add_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
 343         __set_bit(rt_se_prio(rt_se), array->bitmap);
 344
 345         inc_rt_tasks(rt_se, rt_rq);
 346 }
 347
 348 static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
 349 {
 350         struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
 351         struct rt_prio_array *array = &rt_rq->active;
 352
 353         list_del_init(&rt_se->run_list);
 354         if (list_empty(array->queue + rt_se_prio(rt_se)))
 355                 __clear_bit(rt_se_prio(rt_se), array->bitmap);
 356
 357         dec_rt_tasks(rt_se, rt_rq);
 358 }
 359
 360 /*
 361  * Because the prio of an upper entry depends on the lower
 362  * entries, we must remove entries top - down.
 363  *
 364  * XXX: O(1/2 h^2) because we can only walk up, not down the chain.
 365  *      doesn't matter much for now, as h=2 for GROUP_SCHED.
 366  */
 367 static void dequeue_rt_stack(struct task_struct *p)
 368 {
 369         struct sched_rt_entity *rt_se, *top_se;
 370
 371         /*
 372          * dequeue all, top - down.
 373          */
 374         do {
 375                 rt_se = &p->rt;
 376                 top_se = NULL;
 377                 for_each_sched_rt_entity(rt_se) {
 378                         if (on_rt_rq(rt_se))
 379                                 top_se = rt_se;
 380                 }
 381                 if (top_se)
 382                         dequeue_rt_entity(top_se);
 383         } while (top_se);
 384 }
 385
 386 /*
 387  * Adding/removing a task to/from a priority array:
 388  */
 389 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
 390 {
 391         struct sched_rt_entity *rt_se = &p->rt;
 392
 393         if (wakeup)
 394                 rt_se->timeout = 0;
 395
 396         dequeue_rt_stack(p);
 397
 398         /*
 399          * enqueue everybody, bottom - up.
 400          */
 401         for_each_sched_rt_entity(rt_se)
 402                 enqueue_rt_entity(rt_se);
 403
 404         inc_cpu_load(rq, p->se.load.weight);
 405 }
 406
 407 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
 408 {
 409         struct sched_rt_entity *rt_se = &p->rt;
 410         struct rt_rq *rt_rq;
 411
 412         update_curr_rt(rq);
 413
 414         dequeue_rt_stack(p);
 415
 416         /*
 417          * re-enqueue all non-empty rt_rq entities.
 418          */
 419         for_each_sched_rt_entity(rt_se) {
 420                 rt_rq = group_rt_rq(rt_se);
 421                 if (rt_rq && rt_rq->rt_nr_running)
 422                         enqueue_rt_entity(rt_se);
 423         }
 424
 425         dec_cpu_load(rq, p->se.load.weight);
 426 }
 427
 428 /*
 429  * Put task to the end of the run list without the overhead of dequeue
 430  * followed by enqueue.
 431  */
 432 static
 433 void requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se)
 434 {
 435         struct rt_prio_array *array = &rt_rq->active;
 436
 437         list_move_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
 438 }
 439
 440 static void requeue_task_rt(struct rq *rq, struct task_struct *p)
 441 {
 442         struct sched_rt_entity *rt_se = &p->rt;
 443         struct rt_rq *rt_rq;
 444
 445         for_each_sched_rt_entity(rt_se) {
 446                 rt_rq = rt_rq_of_se(rt_se);
 447                 requeue_rt_entity(rt_rq, rt_se);
 448         }
 449 }
 450
 451 static void yield_task_rt(struct rq *rq)
 452 {
 453         requeue_task_rt(rq, rq->curr);
 454 }
 455
 456 #ifdef CONFIG_SMP
 457 static int find_lowest_rq(struct task_struct *task);
 458
 459 static int select_task_rq_rt(struct task_struct *p, int sync)
 460 {
 461         struct rq *rq = task_rq(p);
 462
 463         /*
 464          * If the current task is an RT task, then
 465          * try to see if we can wake this RT task up on another
 466          * runqueue. Otherwise simply start this RT task
 467          * on its current runqueue.
 468          *
 469          * We want to avoid overloading runqueues. Even if
 470          * the RT task is of higher priority than the current RT task.
 471          * RT tasks behave differently than other tasks. If
 472          * one gets preempted, we try to push it off to another queue.
 473          * So trying to keep a preempting RT task on the same
 474          * cache hot CPU will force the running RT task to
 475          * a cold CPU. So we waste all the cache for the lower
 476          * RT task in hopes of saving some of a RT task
 477          * that is just being woken and probably will have
 478          * cold cache anyway.
 479          */
 480         if (unlikely(rt_task(rq->curr)) &&
 481             (p->rt.nr_cpus_allowed > 1)) {
 482                 int cpu = find_lowest_rq(p);
 483
 484                 return (cpu == -1) ? task_cpu(p) : cpu;
 485         }
 486
 487         /*
 488          * Otherwise, just let it ride on the affined RQ and the
 489          * post-schedule router will push the preempted task away
 490          */
 491         return task_cpu(p);
 492 }
 493 #endif /* CONFIG_SMP */
 494
 495 /*
 496  * Preempt the current task with a newly woken task if needed:
 497  */
 498 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
 499 {
 500         if (p->prio < rq->curr->prio)
 501                 resched_task(rq->curr);
 502 }
 503
 504 static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
 505                                                    struct rt_rq *rt_rq)
 506 {
 507         struct rt_prio_array *array = &rt_rq->active;
 508         struct sched_rt_entity *next = NULL;
 509         struct list_head *queue;
 510         int idx;
 511
 512         idx = sched_find_first_bit(array->bitmap);
 513         BUG_ON(idx >= MAX_RT_PRIO);
 514
 515         queue = array->queue + idx;
 516         next = list_entry(queue->next, struct sched_rt_entity, run_list);
 517
 518         return next;
 519 }
 520
 521 static struct task_struct *pick_next_task_rt(struct rq *rq)
 522 {
 523         struct sched_rt_entity *rt_se;
 524         struct task_struct *p;
 525         struct rt_rq *rt_rq;
 526
 527         rt_rq = &rq->rt;
 528
 529         if (unlikely(!rt_rq->rt_nr_running))
 530                 return NULL;
 531
 532         if (rt_rq_throttled(rt_rq))
 533                 return NULL;
 534
 535         do {
 536                 rt_se = pick_next_rt_entity(rq, rt_rq);
 537                 BUG_ON(!rt_se);
 538                 rt_rq = group_rt_rq(rt_se);
 539         } while (rt_rq);
 540
 541         p = rt_task_of(rt_se);
 542         p->se.exec_start = rq->clock;
 543         return p;
 544 }
 545
 546 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 547 {
 548         update_curr_rt(rq);
 549         p->se.exec_start = 0;
 550 }
 551
 552 #ifdef CONFIG_SMP
 553
 554 /* Only try algorithms three times */
 555 #define RT_MAX_TRIES 3
 556
 557 static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
 558 static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
 559
 560 static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
 561 {
 562         if (!task_running(rq, p) &&
 563             (cpu < 0 || cpu_isset(cpu, p->cpus_allowed)) &&
 564             (p->rt.nr_cpus_allowed > 1))
 565                 return 1;
 566         return 0;
 567 }
 568
 569 /* Return the second highest RT task, NULL otherwise */
 570 static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu)
 571 {
 572         struct task_struct *next = NULL;
 573         struct sched_rt_entity *rt_se;
 574         struct rt_prio_array *array;
 575         struct rt_rq *rt_rq;
 576         int idx;
 577
 578         for_each_leaf_rt_rq(rt_rq, rq) {
 579                 array = &rt_rq->active;
 580                 idx = sched_find_first_bit(array->bitmap);
 581  next_idx:
 582                 if (idx >= MAX_RT_PRIO)
 583                         continue;
 584                 if (next && next->prio < idx)
 585                         continue;
 586                 list_for_each_entry(rt_se, array->queue + idx, run_list) {
 587                         struct task_struct *p = rt_task_of(rt_se);
 588                         if (pick_rt_task(rq, p, cpu)) {
 589                                 next = p;
 590                                 break;
 591                         }
 592                 }
 593                 if (!next) {
 594                         idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
 595                         goto next_idx;
 596                 }
 597         }
 598
 599         return next;
 600 }
 601
 602 static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
 603
 604 static int find_lowest_cpus(struct task_struct *task, cpumask_t *lowest_mask)
 605 {
 606         int       lowest_prio = -1;
 607         int       lowest_cpu  = -1;
 608         int       count       = 0;
 609         int       cpu;
 610
 611         cpus_and(*lowest_mask, task_rq(task)->rd->online, task->cpus_allowed);
 612
 613         /*
 614          * Scan each rq for the lowest prio.
 615          */
 616         for_each_cpu_mask(cpu, *lowest_mask) {
 617                 struct rq *rq = cpu_rq(cpu);
 618
 619                 /* We look for lowest RT prio or non-rt CPU */
 620                 if (rq->rt.highest_prio >= MAX_RT_PRIO) {
 621                         /*
 622                          * if we already found a low RT queue
 623                          * and now we found this non-rt queue
 624                          * clear the mask and set our bit.
 625                          * Otherwise just return the queue as is
 626                          * and the count==1 will cause the algorithm
 627                          * to use the first bit found.
 628                          */
 629                         if (lowest_cpu != -1) {
 630                                 cpus_clear(*lowest_mask);
 631                                 cpu_set(rq->cpu, *lowest_mask);
 632                         }
 633                         return 1;
 634                 }
 635
 636                 /* no locking for now */
 637                 if ((rq->rt.highest_prio > task->prio)
 638                     && (rq->rt.highest_prio >= lowest_prio)) {
 639                         if (rq->rt.highest_prio > lowest_prio) {
 640                                 /* new low - clear old data */
 641                                 lowest_prio = rq->rt.highest_prio;
 642                                 lowest_cpu = cpu;
 643                                 count = 0;
 644                         }
 645                         count++;
 646                 } else
 647                         cpu_clear(cpu, *lowest_mask);
 648         }
 649
 650         /*
 651          * Clear out all the set bits that represent
 652          * runqueues that were of higher prio than
 653          * the lowest_prio.
 654          */
 655         if (lowest_cpu > 0) {
 656                 /*
 657                  * Perhaps we could add another cpumask op to
 658                  * zero out bits. Like cpu_zero_bits(cpumask, nrbits);
 659                  * Then that could be optimized to use memset and such.
 660                  */
 661                 for_each_cpu_mask(cpu, *lowest_mask) {
 662                         if (cpu >= lowest_cpu)
 663                                 break;
 664                         cpu_clear(cpu, *lowest_mask);
 665                 }
 666         }
 667
 668         return count;
 669 }
 670
 671 static inline int pick_optimal_cpu(int this_cpu, cpumask_t *mask)
 672 {
 673         int first;
 674
 675         /* "this_cpu" is cheaper to preempt than a remote processor */
 676         if ((this_cpu != -1) && cpu_isset(this_cpu, *mask))
 677                 return this_cpu;
 678
 679         first = first_cpu(*mask);
 680         if (first != NR_CPUS)
 681                 return first;
 682
 683         return -1;
 684 }
 685
 686 static int find_lowest_rq(struct task_struct *task)
 687 {
 688         struct sched_domain *sd;
 689         cpumask_t *lowest_mask = &__get_cpu_var(local_cpu_mask);
 690         int this_cpu = smp_processor_id();
 691         int cpu      = task_cpu(task);
 692         int count    = find_lowest_cpus(task, lowest_mask);
 693
 694         if (!count)
 695                 return -1; /* No targets found */
 696
 697         /*
 698          * There is no sense in performing an optimal search if only one
 699          * target is found.
 700          */
 701         if (count == 1)
 702                 return first_cpu(*lowest_mask);
 703
 704         /*
 705          * At this point we have built a mask of cpus representing the
 706          * lowest priority tasks in the system.  Now we want to elect
 707          * the best one based on our affinity and topology.
 708          *
 709          * We prioritize the last cpu that the task executed on since
 710          * it is most likely cache-hot in that location.
 711          */
 712         if (cpu_isset(cpu, *lowest_mask))
 713                 return cpu;
 714
 715         /*
 716          * Otherwise, we consult the sched_domains span maps to figure
 717          * out which cpu is logically closest to our hot cache data.
 718          */
 719         if (this_cpu == cpu)
 720                 this_cpu = -1; /* Skip this_cpu opt if the same */
 721
 722         for_each_domain(cpu, sd) {
 723                 if (sd->flags & SD_WAKE_AFFINE) {
 724                         cpumask_t domain_mask;
 725                         int       best_cpu;
 726
 727                         cpus_and(domain_mask, sd->span, *lowest_mask);
 728
 729                         best_cpu = pick_optimal_cpu(this_cpu,
 730                                                     &domain_mask);
 731                         if (best_cpu != -1)
 732                                 return best_cpu;
 733                 }
 734         }
 735
 736         /*
 737          * And finally, if there were no matches within the domains
 738          * just give the caller *something* to work with from the compatible
 739          * locations.
 740          */
 741         return pick_optimal_cpu(this_cpu, lowest_mask);
 742 }
 743
 744 /* Will lock the rq it finds */
 745 static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
 746 {
 747         struct rq *lowest_rq = NULL;
 748         int tries;
 749         int cpu;
 750
 751         for (tries = 0; tries < RT_MAX_TRIES; tries++) {
 752                 cpu = find_lowest_rq(task);
 753
 754                 if ((cpu == -1) || (cpu == rq->cpu))
 755                         break;
 756
 757                 lowest_rq = cpu_rq(cpu);
 758
 759                 /* if the prio of this runqueue changed, try again */
 760                 if (double_lock_balance(rq, lowest_rq)) {
 761                         /*
 762                          * We had to unlock the run queue. In
 763                          * the mean time, task could have
 764                          * migrated already or had its affinity changed.
 765                          * Also make sure that it wasn't scheduled on its rq.
 766                          */
 767                         if (unlikely(task_rq(task) != rq ||
 768                                      !cpu_isset(lowest_rq->cpu,
 769                                                 task->cpus_allowed) ||
 770                                      task_running(rq, task) ||
 771                                      !task->se.on_rq)) {
 772
 773                                 spin_unlock(&lowest_rq->lock);
 774                                 lowest_rq = NULL;
 775                                 break;
 776                         }
 777                 }
 778
 779                 /* If this rq is still suitable use it. */
 780                 if (lowest_rq->rt.highest_prio > task->prio)
 781                         break;
 782
 783                 /* try again */
 784                 spin_unlock(&lowest_rq->lock);
 785                 lowest_rq = NULL;
 786         }
 787
 788         return lowest_rq;
 789 }
 790
 791 /*
 792  * If the current CPU has more than one RT task, see if the non
 793  * running task can migrate over to a CPU that is running a task
 794  * of lesser priority.
 795  */
 796 static int push_rt_task(struct rq *rq)
 797 {
 798         struct task_struct *next_task;
 799         struct rq *lowest_rq;
 800         int ret = 0;
 801         int paranoid = RT_MAX_TRIES;
 802
 803         if (!rq->rt.overloaded)
 804                 return 0;
 805
 806         next_task = pick_next_highest_task_rt(rq, -1);
 807         if (!next_task)
 808                 return 0;
 809
 810  retry:
 811         if (unlikely(next_task == rq->curr)) {
 812                 WARN_ON(1);
 813                 return 0;
 814         }
 815
 816         /*
 817          * It's possible that the next_task slipped in of
 818          * higher priority than current. If that's the case
 819          * just reschedule current.
 820          */
 821         if (unlikely(next_task->prio < rq->curr->prio)) {
 822                 resched_task(rq->curr);
 823                 return 0;
 824         }
 825
 826         /* We might release rq lock */
 827         get_task_struct(next_task);
 828
 829         /* find_lock_lowest_rq locks the rq if found */
 830         lowest_rq = find_lock_lowest_rq(next_task, rq);
 831         if (!lowest_rq) {
 832                 struct task_struct *task;
 833                 /*
 834                  * find lock_lowest_rq releases rq->lock
 835                  * so it is possible that next_task has changed.
 836                  * If it has, then try again.
 837                  */
 838                 task = pick_next_highest_task_rt(rq, -1);
 839                 if (unlikely(task != next_task) && task && paranoid--) {
 840                         put_task_struct(next_task);
 841                         next_task = task;
 842                         goto retry;
 843                 }
 844                 goto out;
 845         }
 846
 847         deactivate_task(rq, next_task, 0);
 848         set_task_cpu(next_task, lowest_rq->cpu);
 849         activate_task(lowest_rq, next_task, 0);
 850
 851         resched_task(lowest_rq->curr);
 852
 853         spin_unlock(&lowest_rq->lock);
 854
 855         ret = 1;
 856 out:
 857         put_task_struct(next_task);
 858
 859         return ret;
 860 }
 861
 862 /*
 863  * TODO: Currently we just use the second highest prio task on
 864  *       the queue, and stop when it can't migrate (or there's
 865  *       no more RT tasks).  There may be a case where a lower
 866  *       priority RT task has a different affinity than the
 867  *       higher RT task. In this case the lower RT task could
 868  *       possibly be able to migrate where as the higher priority
 869  *       RT task could not.  We currently ignore this issue.
 870  *       Enhancements are welcome!
 871  */
 872 static void push_rt_tasks(struct rq *rq)
 873 {
 874         /* push_rt_task will return true if it moved an RT */
 875         while (push_rt_task(rq))
 876                 ;
 877 }
 878
 879 static int pull_rt_task(struct rq *this_rq)
 880 {
 881         int this_cpu = this_rq->cpu, ret = 0, cpu;
 882         struct task_struct *p, *next;
 883         struct rq *src_rq;
 884
 885         if (likely(!rt_overloaded(this_rq)))
 886                 return 0;
 887
 888         next = pick_next_task_rt(this_rq);
 889
 890         for_each_cpu_mask(cpu, this_rq->rd->rto_mask) {
 891                 if (this_cpu == cpu)
 892                         continue;
 893
 894                 src_rq = cpu_rq(cpu);
 895                 /*
 896                  * We can potentially drop this_rq's lock in
 897                  * double_lock_balance, and another CPU could
 898                  * steal our next task - hence we must cause
 899                  * the caller to recalculate the next task
 900                  * in that case:
 901                  */
 902                 if (double_lock_balance(this_rq, src_rq)) {
 903                         struct task_struct *old_next = next;
 904
 905                         next = pick_next_task_rt(this_rq);
 906                         if (next != old_next)
 907                                 ret = 1;
 908                 }
 909
 910                 /*
 911                  * Are there still pullable RT tasks?
 912                  */
 913                 if (src_rq->rt.rt_nr_running <= 1)
 914                         goto skip;
 915
 916                 p = pick_next_highest_task_rt(src_rq, this_cpu);
 917
 918                 /*
 919                  * Do we have an RT task that preempts
 920                  * the to-be-scheduled task?
 921                  */
 922                 if (p && (!next || (p->prio < next->prio))) {
 923                         WARN_ON(p == src_rq->curr);
 924                         WARN_ON(!p->se.on_rq);
 925
 926                         /*
 927                          * There's a chance that p is higher in priority
 928                          * than what's currently running on its cpu.
 929                          * This is just that p is wakeing up and hasn't
 930                          * had a chance to schedule. We only pull
 931                          * p if it is lower in priority than the
 932                          * current task on the run queue or
 933                          * this_rq next task is lower in prio than
 934                          * the current task on that rq.
 935                          */
 936                         if (p->prio < src_rq->curr->prio ||
 937                             (next && next->prio < src_rq->curr->prio))
 938                                 goto skip;
 939
 940                         ret = 1;
 941
 942                         deactivate_task(src_rq, p, 0);
 943                         set_task_cpu(p, this_cpu);
 944                         activate_task(this_rq, p, 0);
 945                         /*
 946                          * We continue with the search, just in
 947                          * case there's an even higher prio task
 948                          * in another runqueue. (low likelyhood
 949                          * but possible)
 950                          *
 951                          * Update next so that we won't pick a task
 952                          * on another cpu with a priority lower (or equal)
 953                          * than the one we just picked.
 954                          */
 955                         next = p;
 956
 957                 }
 958  skip:
 959                 spin_unlock(&src_rq->lock);
 960         }
 961
 962         return ret;
 963 }
 964
 965 static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
 966 {
 967         /* Try to pull RT tasks here if we lower this rq's prio */
 968         if (unlikely(rt_task(prev)) && rq->rt.highest_prio > prev->prio)
 969                 pull_rt_task(rq);
 970 }
 971
 972 static void post_schedule_rt(struct rq *rq)
 973 {
 974         /*
 975          * If we have more than one rt_task queued, then
 976          * see if we can push the other rt_tasks off to other CPUS.
 977          * Note we may release the rq lock, and since
 978          * the lock was owned by prev, we need to release it
 979          * first via finish_lock_switch and then reaquire it here.
 980          */
 981         if (unlikely(rq->rt.overloaded)) {
 982                 spin_lock_irq(&rq->lock);
 983                 push_rt_tasks(rq);
 984                 spin_unlock_irq(&rq->lock);
 985         }
 986 }
 987
 988
 989 static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
 990 {
 991         if (!task_running(rq, p) &&
 992             (p->prio >= rq->rt.highest_prio) &&
 993             rq->rt.overloaded)
 994                 push_rt_tasks(rq);
 995 }
 996
 997 static unsigned long
 998 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 999                 unsigned long max_load_move,
1000                 struct sched_domain *sd, enum cpu_idle_type idle,
1001                 int *all_pinned, int *this_best_prio)
1002 {
1003         /* don't touch RT tasks */
1004         return 0;
1005 }
1006
1007 static int
1008 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
1009                  struct sched_domain *sd, enum cpu_idle_type idle)
1010 {
1011         /* don't touch RT tasks */
1012         return 0;
1013 }
1014
1015 static void set_cpus_allowed_rt(struct task_struct *p, cpumask_t *new_mask)
1016 {
1017         int weight = cpus_weight(*new_mask);
1018
1019         BUG_ON(!rt_task(p));
1020
1021         /*
1022          * Update the migration status of the RQ if we have an RT task
1023          * which is running AND changing its weight value.
1024          */
1025         if (p->se.on_rq && (weight != p->rt.nr_cpus_allowed)) {
1026                 struct rq *rq = task_rq(p);
1027
1028                 if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) {
1029                         rq->rt.rt_nr_migratory++;
1030                 } else if ((p->rt.nr_cpus_allowed > 1) && (weight <= 1)) {
1031                         BUG_ON(!rq->rt.rt_nr_migratory);
1032                         rq->rt.rt_nr_migratory--;
1033                 }
1034
1035                 update_rt_migration(rq);
1036         }
1037
1038         p->cpus_allowed    = *new_mask;
1039         p->rt.nr_cpus_allowed = weight;
1040 }
1041
1042 /* Assumes rq->lock is held */
1043 static void join_domain_rt(struct rq *rq)
1044 {
1045         if (rq->rt.overloaded)
1046                 rt_set_overload(rq);
1047 }
1048
1049 /* Assumes rq->lock is held */
1050 static void leave_domain_rt(struct rq *rq)
1051 {
1052         if (rq->rt.overloaded)
1053                 rt_clear_overload(rq);
1054 }
1055
1056 /*
1057  * When switch from the rt queue, we bring ourselves to a position
1058  * that we might want to pull RT tasks from other runqueues.
1059  */
1060 static void switched_from_rt(struct rq *rq, struct task_struct *p,
1061                            int running)
1062 {
1063         /*
1064          * If there are other RT tasks then we will reschedule
1065          * and the scheduling of the other RT tasks will handle
1066          * the balancing. But if we are the last RT task
1067          * we may need to handle the pulling of RT tasks
1068          * now.
1069          */
1070         if (!rq->rt.rt_nr_running)
1071                 pull_rt_task(rq);
1072 }
1073 #endif /* CONFIG_SMP */
1074
1075 /*
1076  * When switching a task to RT, we may overload the runqueue
1077  * with RT tasks. In this case we try to push them off to
1078  * other runqueues.
1079  */
1080 static void switched_to_rt(struct rq *rq, struct task_struct *p,
1081                            int running)
1082 {
1083         int check_resched = 1;
1084
1085         /*
1086          * If we are already running, then there's nothing
1087          * that needs to be done. But if we are not running
1088          * we may need to preempt the current running task.
1089          * If that current running task is also an RT task
1090          * then see if we can move to another run queue.
1091          */
1092         if (!running) {
1093 #ifdef CONFIG_SMP
1094                 if (rq->rt.overloaded && push_rt_task(rq) &&
1095                     /* Don't resched if we changed runqueues */
1096                     rq != task_rq(p))
1097                         check_resched = 0;
1098 #endif /* CONFIG_SMP */
1099                 if (check_resched && p->prio < rq->curr->prio)
1100                         resched_task(rq->curr);
1101         }
1102 }
1103
1104 /*
1105  * Priority of the task has changed. This may cause
1106  * us to initiate a push or pull.
1107  */
1108 static void prio_changed_rt(struct rq *rq, struct task_struct *p,
1109                             int oldprio, int running)
1110 {
1111         if (running) {
1112 #ifdef CONFIG_SMP
1113                 /*
1114                  * If our priority decreases while running, we
1115                  * may need to pull tasks to this runqueue.
1116                  */
1117                 if (oldprio < p->prio)
1118                         pull_rt_task(rq);
1119                 /*
1120                  * If there's a higher priority task waiting to run
1121                  * then reschedule.
1122                  */
1123                 if (p->prio > rq->rt.highest_prio)
1124                         resched_task(p);
1125 #else
1126                 /* For UP simply resched on drop of prio */
1127                 if (oldprio < p->prio)
1128                         resched_task(p);
1129 #endif /* CONFIG_SMP */
1130         } else {
1131                 /*
1132                  * This task is not running, but if it is
1133                  * greater than the current running task
1134                  * then reschedule.
1135                  */
1136                 if (p->prio < rq->curr->prio)
1137                         resched_task(rq->curr);
1138         }
1139 }
1140
1141 static void watchdog(struct rq *rq, struct task_struct *p)
1142 {
1143         unsigned long soft, hard;
1144
1145         if (!p->signal)
1146                 return;
1147
1148         soft = p->signal->rlim[RLIMIT_RTTIME].rlim_cur;
1149         hard = p->signal->rlim[RLIMIT_RTTIME].rlim_max;
1150
1151         if (soft != RLIM_INFINITY) {
1152                 unsigned long next;
1153
1154                 p->rt.timeout++;
1155                 next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
1156                 if (p->rt.timeout > next)
1157                         p->it_sched_expires = p->se.sum_exec_runtime;
1158         }
1159 }
1160
1161 static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
1162 {
1163         update_curr_rt(rq);
1164
1165         watchdog(rq, p);
1166
1167         /*
1168          * RR tasks need a special form of timeslice management.
1169          * FIFO tasks have no timeslices.
1170          */
1171         if (p->policy != SCHED_RR)
1172                 return;
1173
1174         if (--p->rt.time_slice)
1175                 return;
1176
1177         p->rt.time_slice = DEF_TIMESLICE;
1178
1179         /*
1180          * Requeue to the end of queue if we are not the only element
1181          * on the queue:
1182          */
1183         if (p->rt.run_list.prev != p->rt.run_list.next) {
1184                 requeue_task_rt(rq, p);
1185                 set_tsk_need_resched(p);
1186         }
1187 }
1188
1189 static void set_curr_task_rt(struct rq *rq)
1190 {
1191         struct task_struct *p = rq->curr;
1192
1193         p->se.exec_start = rq->clock;
1194 }
1195
1196 const struct sched_class rt_sched_class = {
1197         .next                   = &fair_sched_class,
1198         .enqueue_task           = enqueue_task_rt,
1199         .dequeue_task           = dequeue_task_rt,
1200         .yield_task             = yield_task_rt,
1201 #ifdef CONFIG_SMP
1202         .select_task_rq         = select_task_rq_rt,
1203 #endif /* CONFIG_SMP */
1204
1205         .check_preempt_curr     = check_preempt_curr_rt,
1206
1207         .pick_next_task         = pick_next_task_rt,
1208         .put_prev_task          = put_prev_task_rt,
1209
1210 #ifdef CONFIG_SMP
1211         .load_balance           = load_balance_rt,
1212         .move_one_task          = move_one_task_rt,
1213         .set_cpus_allowed       = set_cpus_allowed_rt,
1214         .join_domain            = join_domain_rt,
1215         .leave_domain           = leave_domain_rt,
1216         .pre_schedule           = pre_schedule_rt,
1217         .post_schedule          = post_schedule_rt,
1218         .task_wake_up           = task_wake_up_rt,
1219         .switched_from          = switched_from_rt,
1220 #endif
1221
1222         .set_curr_task          = set_curr_task_rt,
1223         .task_tick              = task_tick_rt,
1224
1225         .prio_changed           = prio_changed_rt,
1226         .switched_to            = switched_to_rt,
1227 };