drivers/gpu/drm/i915/i915_scheduler.c

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright © 2018 Intel Corporation
   5  */
   6
   7 #include <linux/mutex.h>
   8
   9 #include "i915_drv.h"
  10 #include "i915_globals.h"
  11 #include "i915_request.h"
  12 #include "i915_scheduler.h"
  13
  14 static struct i915_global_scheduler {
  15         struct i915_global base;
  16         struct kmem_cache *slab_dependencies;
  17         struct kmem_cache *slab_priorities;
  18 } global;
  19
  20 static DEFINE_SPINLOCK(schedule_lock);
  21
  22 static const struct i915_request *
  23 node_to_request(const struct i915_sched_node *node)
  24 {
  25         return container_of(node, const struct i915_request, sched);
  26 }
  27
  28 static inline bool node_started(const struct i915_sched_node *node)
  29 {
  30         return i915_request_started(node_to_request(node));
  31 }
  32
  33 static inline bool node_signaled(const struct i915_sched_node *node)
  34 {
  35         return i915_request_completed(node_to_request(node));
  36 }
  37
  38 static inline struct i915_priolist *to_priolist(struct rb_node *rb)
  39 {
  40         return rb_entry(rb, struct i915_priolist, node);
  41 }
  42
  43 static void assert_priolists(struct intel_engine_execlists * const execlists)
  44 {
  45         struct rb_node *rb;
  46         long last_prio, i;
  47
  48         if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
  49                 return;
  50
  51         GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
  52                    rb_first(&execlists->queue.rb_root));
  53
  54         last_prio = INT_MAX;
  55         for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
  56                 const struct i915_priolist *p = to_priolist(rb);
  57
  58                 GEM_BUG_ON(p->priority > last_prio);
  59                 last_prio = p->priority;
  60
  61                 GEM_BUG_ON(!p->used);
  62                 for (i = 0; i < ARRAY_SIZE(p->requests); i++) {
  63                         if (list_empty(&p->requests[i]))
  64                                 continue;
  65
  66                         GEM_BUG_ON(!(p->used & BIT(i)));
  67                 }
  68         }
  69 }
  70
  71 struct list_head *
  72 i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
  73 {
  74         struct intel_engine_execlists * const execlists = &engine->execlists;
  75         struct i915_priolist *p;
  76         struct rb_node **parent, *rb;
  77         bool first = true;
  78         int idx, i;
  79
  80         lockdep_assert_held(&engine->active.lock);
  81         assert_priolists(execlists);
  82
  83         /* buckets sorted from highest [in slot 0] to lowest priority */
  84         idx = I915_PRIORITY_COUNT - (prio & I915_PRIORITY_MASK) - 1;
  85         prio >>= I915_USER_PRIORITY_SHIFT;
  86         if (unlikely(execlists->no_priolist))
  87                 prio = I915_PRIORITY_NORMAL;
  88
  89 find_priolist:
  90         /* most positive priority is scheduled first, equal priorities fifo */
  91         rb = NULL;
  92         parent = &execlists->queue.rb_root.rb_node;
  93         while (*parent) {
  94                 rb = *parent;
  95                 p = to_priolist(rb);
  96                 if (prio > p->priority) {
  97                         parent = &rb->rb_left;
  98                 } else if (prio < p->priority) {
  99                         parent = &rb->rb_right;
 100                         first = false;
 101                 } else {
 102                         goto out;
 103                 }
 104         }
 105
 106         if (prio == I915_PRIORITY_NORMAL) {
 107                 p = &execlists->default_priolist;
 108         } else {
 109                 p = kmem_cache_alloc(global.slab_priorities, GFP_ATOMIC);
 110                 /* Convert an allocation failure to a priority bump */
 111                 if (unlikely(!p)) {
 112                         prio = I915_PRIORITY_NORMAL; /* recurses just once */
 113
 114                         /* To maintain ordering with all rendering, after an
 115                          * allocation failure we have to disable all scheduling.
 116                          * Requests will then be executed in fifo, and schedule
 117                          * will ensure that dependencies are emitted in fifo.
 118                          * There will be still some reordering with existing
 119                          * requests, so if userspace lied about their
 120                          * dependencies that reordering may be visible.
 121                          */
 122                         execlists->no_priolist = true;
 123                         goto find_priolist;
 124                 }
 125         }
 126
 127         p->priority = prio;
 128         for (i = 0; i < ARRAY_SIZE(p->requests); i++)
 129                 INIT_LIST_HEAD(&p->requests[i]);
 130         rb_link_node(&p->node, rb, parent);
 131         rb_insert_color_cached(&p->node, &execlists->queue, first);
 132         p->used = 0;
 133
 134 out:
 135         p->used |= BIT(idx);
 136         return &p->requests[idx];
 137 }
 138
 139 void __i915_priolist_free(struct i915_priolist *p)
 140 {
 141         kmem_cache_free(global.slab_priorities, p);
 142 }
 143
 144 struct sched_cache {
 145         struct list_head *priolist;
 146 };
 147
 148 static struct intel_engine_cs *
 149 sched_lock_engine(const struct i915_sched_node *node,
 150                   struct intel_engine_cs *locked,
 151                   struct sched_cache *cache)
 152 {
 153         const struct i915_request *rq = node_to_request(node);
 154         struct intel_engine_cs *engine;
 155
 156         GEM_BUG_ON(!locked);
 157
 158         /*
 159          * Virtual engines complicate acquiring the engine timeline lock,
 160          * as their rq->engine pointer is not stable until under that
 161          * engine lock. The simple ploy we use is to take the lock then
 162          * check that the rq still belongs to the newly locked engine.
 163          */
 164         while (locked != (engine = READ_ONCE(rq->engine))) {
 165                 spin_unlock(&locked->active.lock);
 166                 memset(cache, 0, sizeof(*cache));
 167                 spin_lock(&engine->active.lock);
 168                 locked = engine;
 169         }
 170
 171         GEM_BUG_ON(locked != engine);
 172         return locked;
 173 }
 174
 175 static inline int rq_prio(const struct i915_request *rq)
 176 {
 177         return rq->sched.attr.priority;
 178 }
 179
 180 static inline bool need_preempt(int prio, int active)
 181 {
 182         /*
 183          * Allow preemption of low -> normal -> high, but we do
 184          * not allow low priority tasks to preempt other low priority
 185          * tasks under the impression that latency for low priority
 186          * tasks does not matter (as much as background throughput),
 187          * so kiss.
 188          */
 189         return prio >= max(I915_PRIORITY_NORMAL, active);
 190 }
 191
 192 static void kick_submission(struct intel_engine_cs *engine,
 193                             const struct i915_request *rq,
 194                             int prio)
 195 {
 196         const struct i915_request *inflight;
 197
 198         /*
 199          * We only need to kick the tasklet once for the high priority
 200          * new context we add into the queue.
 201          */
 202         if (prio <= engine->execlists.queue_priority_hint)
 203                 return;
 204
 205         rcu_read_lock();
 206
 207         /* Nothing currently active? We're overdue for a submission! */
 208         inflight = execlists_active(&engine->execlists);
 209         if (!inflight)
 210                 goto unlock;
 211
 212         /*
 213          * If we are already the currently executing context, don't
 214          * bother evaluating if we should preempt ourselves.
 215          */
 216         if (inflight->context == rq->context)
 217                 goto unlock;
 218
 219         ENGINE_TRACE(engine,
 220                      "bumping queue-priority-hint:%d for rq:%llx:%lld, inflight:%llx:%lld prio %d\n",
 221                      prio,
 222                      rq->fence.context, rq->fence.seqno,
 223                      inflight->fence.context, inflight->fence.seqno,
 224                      inflight->sched.attr.priority);
 225
 226         engine->execlists.queue_priority_hint = prio;
 227         if (need_preempt(prio, rq_prio(inflight)))
 228                 tasklet_hi_schedule(&engine->execlists.tasklet);
 229
 230 unlock:
 231         rcu_read_unlock();
 232 }
 233
 234 static void __i915_schedule(struct i915_sched_node *node,
 235                             const struct i915_sched_attr *attr)
 236 {
 237         const int prio = max(attr->priority, node->attr.priority);
 238         struct intel_engine_cs *engine;
 239         struct i915_dependency *dep, *p;
 240         struct i915_dependency stack;
 241         struct sched_cache cache;
 242         LIST_HEAD(dfs);
 243
 244         /* Needed in order to use the temporary link inside i915_dependency */
 245         lockdep_assert_held(&schedule_lock);
 246         GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
 247
 248         if (node_signaled(node))
 249                 return;
 250
 251         stack.signaler = node;
 252         list_add(&stack.dfs_link, &dfs);
 253
 254         /*
 255          * Recursively bump all dependent priorities to match the new request.
 256          *
 257          * A naive approach would be to use recursion:
 258          * static void update_priorities(struct i915_sched_node *node, prio) {
 259          *      list_for_each_entry(dep, &node->signalers_list, signal_link)
 260          *              update_priorities(dep->signal, prio)
 261          *      queue_request(node);
 262          * }
 263          * but that may have unlimited recursion depth and so runs a very
 264          * real risk of overunning the kernel stack. Instead, we build
 265          * a flat list of all dependencies starting with the current request.
 266          * As we walk the list of dependencies, we add all of its dependencies
 267          * to the end of the list (this may include an already visited
 268          * request) and continue to walk onwards onto the new dependencies. The
 269          * end result is a topological list of requests in reverse order, the
 270          * last element in the list is the request we must execute first.
 271          */
 272         list_for_each_entry(dep, &dfs, dfs_link) {
 273                 struct i915_sched_node *node = dep->signaler;
 274
 275                 /* If we are already flying, we know we have no signalers */
 276                 if (node_started(node))
 277                         continue;
 278
 279                 /*
 280                  * Within an engine, there can be no cycle, but we may
 281                  * refer to the same dependency chain multiple times
 282                  * (redundant dependencies are not eliminated) and across
 283                  * engines.
 284                  */
 285                 list_for_each_entry(p, &node->signalers_list, signal_link) {
 286                         GEM_BUG_ON(p == dep); /* no cycles! */
 287
 288                         if (node_signaled(p->signaler))
 289                                 continue;
 290
 291                         if (prio > READ_ONCE(p->signaler->attr.priority))
 292                                 list_move_tail(&p->dfs_link, &dfs);
 293                 }
 294         }
 295
 296         /*
 297          * If we didn't need to bump any existing priorities, and we haven't
 298          * yet submitted this request (i.e. there is no potential race with
 299          * execlists_submit_request()), we can set our own priority and skip
 300          * acquiring the engine locks.
 301          */
 302         if (node->attr.priority == I915_PRIORITY_INVALID) {
 303                 GEM_BUG_ON(!list_empty(&node->link));
 304                 node->attr = *attr;
 305
 306                 if (stack.dfs_link.next == stack.dfs_link.prev)
 307                         return;
 308
 309                 __list_del_entry(&stack.dfs_link);
 310         }
 311
 312         memset(&cache, 0, sizeof(cache));
 313         engine = node_to_request(node)->engine;
 314         spin_lock(&engine->active.lock);
 315
 316         /* Fifo and depth-first replacement ensure our deps execute before us */
 317         engine = sched_lock_engine(node, engine, &cache);
 318         list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
 319                 INIT_LIST_HEAD(&dep->dfs_link);
 320
 321                 node = dep->signaler;
 322                 engine = sched_lock_engine(node, engine, &cache);
 323                 lockdep_assert_held(&engine->active.lock);
 324
 325                 /* Recheck after acquiring the engine->timeline.lock */
 326                 if (prio <= node->attr.priority || node_signaled(node))
 327                         continue;
 328
 329                 GEM_BUG_ON(node_to_request(node)->engine != engine);
 330
 331                 WRITE_ONCE(node->attr.priority, prio);
 332
 333                 /*
 334                  * Once the request is ready, it will be placed into the
 335                  * priority lists and then onto the HW runlist. Before the
 336                  * request is ready, it does not contribute to our preemption
 337                  * decisions and we can safely ignore it, as it will, and
 338                  * any preemption required, be dealt with upon submission.
 339                  * See engine->submit_request()
 340                  */
 341                 if (list_empty(&node->link))
 342                         continue;
 343
 344                 if (i915_request_in_priority_queue(node_to_request(node))) {
 345                         if (!cache.priolist)
 346                                 cache.priolist =
 347                                         i915_sched_lookup_priolist(engine,
 348                                                                    prio);
 349                         list_move_tail(&node->link, cache.priolist);
 350                 }
 351
 352                 /* Defer (tasklet) submission until after all of our updates. */
 353                 kick_submission(engine, node_to_request(node), prio);
 354         }
 355
 356         spin_unlock(&engine->active.lock);
 357 }
 358
 359 void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
 360 {
 361         spin_lock_irq(&schedule_lock);
 362         __i915_schedule(&rq->sched, attr);
 363         spin_unlock_irq(&schedule_lock);
 364 }
 365
 366 static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
 367 {
 368         struct i915_sched_attr attr = node->attr;
 369
 370         if (attr.priority & bump)
 371                 return;
 372
 373         attr.priority |= bump;
 374         __i915_schedule(node, &attr);
 375 }
 376
 377 void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
 378 {
 379         unsigned long flags;
 380
 381         GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
 382         if (READ_ONCE(rq->sched.attr.priority) & bump)
 383                 return;
 384
 385         spin_lock_irqsave(&schedule_lock, flags);
 386         __bump_priority(&rq->sched, bump);
 387         spin_unlock_irqrestore(&schedule_lock, flags);
 388 }
 389
 390 void i915_sched_node_init(struct i915_sched_node *node)
 391 {
 392         INIT_LIST_HEAD(&node->signalers_list);
 393         INIT_LIST_HEAD(&node->waiters_list);
 394         INIT_LIST_HEAD(&node->link);
 395
 396         i915_sched_node_reinit(node);
 397 }
 398
 399 void i915_sched_node_reinit(struct i915_sched_node *node)
 400 {
 401         node->attr.priority = I915_PRIORITY_INVALID;
 402         node->semaphores = 0;
 403         node->flags = 0;
 404
 405         GEM_BUG_ON(!list_empty(&node->signalers_list));
 406         GEM_BUG_ON(!list_empty(&node->waiters_list));
 407         GEM_BUG_ON(!list_empty(&node->link));
 408 }
 409
 410 static struct i915_dependency *
 411 i915_dependency_alloc(void)
 412 {
 413         return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
 414 }
 415
 416 static void
 417 i915_dependency_free(struct i915_dependency *dep)
 418 {
 419         kmem_cache_free(global.slab_dependencies, dep);
 420 }
 421
 422 bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
 423                                       struct i915_sched_node *signal,
 424                                       struct i915_dependency *dep,
 425                                       unsigned long flags)
 426 {
 427         bool ret = false;
 428
 429         spin_lock_irq(&schedule_lock);
 430
 431         if (!node_signaled(signal)) {
 432                 INIT_LIST_HEAD(&dep->dfs_link);
 433                 dep->signaler = signal;
 434                 dep->waiter = node;
 435                 dep->flags = flags;
 436
 437                 /* All set, now publish. Beware the lockless walkers. */
 438                 list_add_rcu(&dep->signal_link, &node->signalers_list);
 439                 list_add_rcu(&dep->wait_link, &signal->waiters_list);
 440
 441                 /* Propagate the chains */
 442                 node->flags |= signal->flags;
 443                 ret = true;
 444         }
 445
 446         spin_unlock_irq(&schedule_lock);
 447
 448         return ret;
 449 }
 450
 451 int i915_sched_node_add_dependency(struct i915_sched_node *node,
 452                                    struct i915_sched_node *signal,
 453                                    unsigned long flags)
 454 {
 455         struct i915_dependency *dep;
 456
 457         dep = i915_dependency_alloc();
 458         if (!dep)
 459                 return -ENOMEM;
 460
 461         if (!__i915_sched_node_add_dependency(node, signal, dep,
 462                                               flags | I915_DEPENDENCY_ALLOC))
 463                 i915_dependency_free(dep);
 464
 465         return 0;
 466 }
 467
 468 void i915_sched_node_fini(struct i915_sched_node *node)
 469 {
 470         struct i915_dependency *dep, *tmp;
 471
 472         spin_lock_irq(&schedule_lock);
 473
 474         /*
 475          * Everyone we depended upon (the fences we wait to be signaled)
 476          * should retire before us and remove themselves from our list.
 477          * However, retirement is run independently on each timeline and
 478          * so we may be called out-of-order.
 479          */
 480         list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
 481                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 482
 483                 list_del_rcu(&dep->wait_link);
 484                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 485                         i915_dependency_free(dep);
 486         }
 487         INIT_LIST_HEAD(&node->signalers_list);
 488
 489         /* Remove ourselves from everyone who depends upon us */
 490         list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
 491                 GEM_BUG_ON(dep->signaler != node);
 492                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 493
 494                 list_del_rcu(&dep->signal_link);
 495                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 496                         i915_dependency_free(dep);
 497         }
 498         INIT_LIST_HEAD(&node->waiters_list);
 499
 500         spin_unlock_irq(&schedule_lock);
 501 }
 502
 503 void i915_request_show_with_schedule(struct drm_printer *m,
 504                                      const struct i915_request *rq,
 505                                      const char *prefix,
 506                                      int indent)
 507 {
 508         struct i915_dependency *dep;
 509
 510         i915_request_show(m, rq, prefix, indent);
 511         if (i915_request_completed(rq))
 512                 return;
 513
 514         rcu_read_lock();
 515         for_each_signaler(dep, rq) {
 516                 const struct i915_request *signaler =
 517                         node_to_request(dep->signaler);
 518
 519                 /* Dependencies along the same timeline are expected. */
 520                 if (signaler->timeline == rq->timeline)
 521                         continue;
 522
 523                 if (__i915_request_is_complete(signaler))
 524                         continue;
 525
 526                 i915_request_show(m, signaler, prefix, indent + 2);
 527         }
 528         rcu_read_unlock();
 529 }
 530
 531 static void i915_global_scheduler_shrink(void)
 532 {
 533         kmem_cache_shrink(global.slab_dependencies);
 534         kmem_cache_shrink(global.slab_priorities);
 535 }
 536
 537 static void i915_global_scheduler_exit(void)
 538 {
 539         kmem_cache_destroy(global.slab_dependencies);
 540         kmem_cache_destroy(global.slab_priorities);
 541 }
 542
 543 static struct i915_global_scheduler global = { {
 544         .shrink = i915_global_scheduler_shrink,
 545         .exit = i915_global_scheduler_exit,
 546 } };
 547
 548 int __init i915_global_scheduler_init(void)
 549 {
 550         global.slab_dependencies = KMEM_CACHE(i915_dependency,
 551                                               SLAB_HWCACHE_ALIGN |
 552                                               SLAB_TYPESAFE_BY_RCU);
 553         if (!global.slab_dependencies)
 554                 return -ENOMEM;
 555
 556         global.slab_priorities = KMEM_CACHE(i915_priolist,
 557                                             SLAB_HWCACHE_ALIGN);
 558         if (!global.slab_priorities)
 559                 goto err_priorities;
 560
 561         i915_global_register(&global.base);
 562         return 0;
 563
 564 err_priorities:
 565         kmem_cache_destroy(global.slab_priorities);
 566         return -ENOMEM;
 567 }