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 >> I915_USER_PRIORITY_SHIFT) + 1;
  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 | __NO_PREEMPTION;
 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->hw_context == rq->hw_context)
 217                 goto unlock;
 218
 219         engine->execlists.queue_priority_hint = prio;
 220         if (need_preempt(prio, rq_prio(inflight)))
 221                 tasklet_hi_schedule(&engine->execlists.tasklet);
 222
 223 unlock:
 224         rcu_read_unlock();
 225 }
 226
 227 static void __i915_schedule(struct i915_sched_node *node,
 228                             const struct i915_sched_attr *attr)
 229 {
 230         struct intel_engine_cs *engine;
 231         struct i915_dependency *dep, *p;
 232         struct i915_dependency stack;
 233         const int prio = attr->priority;
 234         struct sched_cache cache;
 235         LIST_HEAD(dfs);
 236
 237         /* Needed in order to use the temporary link inside i915_dependency */
 238         lockdep_assert_held(&schedule_lock);
 239         GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
 240
 241         if (prio <= READ_ONCE(node->attr.priority))
 242                 return;
 243
 244         if (node_signaled(node))
 245                 return;
 246
 247         stack.signaler = node;
 248         list_add(&stack.dfs_link, &dfs);
 249
 250         /*
 251          * Recursively bump all dependent priorities to match the new request.
 252          *
 253          * A naive approach would be to use recursion:
 254          * static void update_priorities(struct i915_sched_node *node, prio) {
 255          *      list_for_each_entry(dep, &node->signalers_list, signal_link)
 256          *              update_priorities(dep->signal, prio)
 257          *      queue_request(node);
 258          * }
 259          * but that may have unlimited recursion depth and so runs a very
 260          * real risk of overunning the kernel stack. Instead, we build
 261          * a flat list of all dependencies starting with the current request.
 262          * As we walk the list of dependencies, we add all of its dependencies
 263          * to the end of the list (this may include an already visited
 264          * request) and continue to walk onwards onto the new dependencies. The
 265          * end result is a topological list of requests in reverse order, the
 266          * last element in the list is the request we must execute first.
 267          */
 268         list_for_each_entry(dep, &dfs, dfs_link) {
 269                 struct i915_sched_node *node = dep->signaler;
 270
 271                 /* If we are already flying, we know we have no signalers */
 272                 if (node_started(node))
 273                         continue;
 274
 275                 /*
 276                  * Within an engine, there can be no cycle, but we may
 277                  * refer to the same dependency chain multiple times
 278                  * (redundant dependencies are not eliminated) and across
 279                  * engines.
 280                  */
 281                 list_for_each_entry(p, &node->signalers_list, signal_link) {
 282                         GEM_BUG_ON(p == dep); /* no cycles! */
 283
 284                         if (node_signaled(p->signaler))
 285                                 continue;
 286
 287                         if (prio > READ_ONCE(p->signaler->attr.priority))
 288                                 list_move_tail(&p->dfs_link, &dfs);
 289                 }
 290         }
 291
 292         /*
 293          * If we didn't need to bump any existing priorities, and we haven't
 294          * yet submitted this request (i.e. there is no potential race with
 295          * execlists_submit_request()), we can set our own priority and skip
 296          * acquiring the engine locks.
 297          */
 298         if (node->attr.priority == I915_PRIORITY_INVALID) {
 299                 GEM_BUG_ON(!list_empty(&node->link));
 300                 node->attr = *attr;
 301
 302                 if (stack.dfs_link.next == stack.dfs_link.prev)
 303                         return;
 304
 305                 __list_del_entry(&stack.dfs_link);
 306         }
 307
 308         memset(&cache, 0, sizeof(cache));
 309         engine = node_to_request(node)->engine;
 310         spin_lock(&engine->active.lock);
 311
 312         /* Fifo and depth-first replacement ensure our deps execute before us */
 313         engine = sched_lock_engine(node, engine, &cache);
 314         list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
 315                 INIT_LIST_HEAD(&dep->dfs_link);
 316
 317                 node = dep->signaler;
 318                 engine = sched_lock_engine(node, engine, &cache);
 319                 lockdep_assert_held(&engine->active.lock);
 320
 321                 /* Recheck after acquiring the engine->timeline.lock */
 322                 if (prio <= node->attr.priority || node_signaled(node))
 323                         continue;
 324
 325                 GEM_BUG_ON(node_to_request(node)->engine != engine);
 326
 327                 node->attr.priority = prio;
 328
 329                 if (list_empty(&node->link)) {
 330                         /*
 331                          * If the request is not in the priolist queue because
 332                          * it is not yet runnable, then it doesn't contribute
 333                          * to our preemption decisions. On the other hand,
 334                          * if the request is on the HW, it too is not in the
 335                          * queue; but in that case we may still need to reorder
 336                          * the inflight requests.
 337                          */
 338                         continue;
 339                 }
 340
 341                 if (!intel_engine_is_virtual(engine) &&
 342                     !i915_request_is_active(node_to_request(node))) {
 343                         if (!cache.priolist)
 344                                 cache.priolist =
 345                                         i915_sched_lookup_priolist(engine,
 346                                                                    prio);
 347                         list_move_tail(&node->link, cache.priolist);
 348                 }
 349
 350                 /* Defer (tasklet) submission until after all of our updates. */
 351                 kick_submission(engine, node_to_request(node), prio);
 352         }
 353
 354         spin_unlock(&engine->active.lock);
 355 }
 356
 357 void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
 358 {
 359         spin_lock_irq(&schedule_lock);
 360         __i915_schedule(&rq->sched, attr);
 361         spin_unlock_irq(&schedule_lock);
 362 }
 363
 364 static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
 365 {
 366         struct i915_sched_attr attr = node->attr;
 367
 368         attr.priority |= bump;
 369         __i915_schedule(node, &attr);
 370 }
 371
 372 void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
 373 {
 374         unsigned long flags;
 375
 376         GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
 377         if (READ_ONCE(rq->sched.attr.priority) & bump)
 378                 return;
 379
 380         spin_lock_irqsave(&schedule_lock, flags);
 381         __bump_priority(&rq->sched, bump);
 382         spin_unlock_irqrestore(&schedule_lock, flags);
 383 }
 384
 385 void i915_sched_node_init(struct i915_sched_node *node)
 386 {
 387         INIT_LIST_HEAD(&node->signalers_list);
 388         INIT_LIST_HEAD(&node->waiters_list);
 389         INIT_LIST_HEAD(&node->link);
 390         node->attr.priority = I915_PRIORITY_INVALID;
 391         node->semaphores = 0;
 392         node->flags = 0;
 393 }
 394
 395 static struct i915_dependency *
 396 i915_dependency_alloc(void)
 397 {
 398         return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
 399 }
 400
 401 static void
 402 i915_dependency_free(struct i915_dependency *dep)
 403 {
 404         kmem_cache_free(global.slab_dependencies, dep);
 405 }
 406
 407 bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
 408                                       struct i915_sched_node *signal,
 409                                       struct i915_dependency *dep,
 410                                       unsigned long flags)
 411 {
 412         bool ret = false;
 413
 414         spin_lock_irq(&schedule_lock);
 415
 416         if (!node_signaled(signal)) {
 417                 INIT_LIST_HEAD(&dep->dfs_link);
 418                 list_add(&dep->wait_link, &signal->waiters_list);
 419                 list_add(&dep->signal_link, &node->signalers_list);
 420                 dep->signaler = signal;
 421                 dep->waiter = node;
 422                 dep->flags = flags;
 423
 424                 /* Keep track of whether anyone on this chain has a semaphore */
 425                 if (signal->flags & I915_SCHED_HAS_SEMAPHORE_CHAIN &&
 426                     !node_started(signal))
 427                         node->flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;
 428
 429                 /*
 430                  * As we do not allow WAIT to preempt inflight requests,
 431                  * once we have executed a request, along with triggering
 432                  * any execution callbacks, we must preserve its ordering
 433                  * within the non-preemptible FIFO.
 434                  */
 435                 BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
 436                 if (flags & I915_DEPENDENCY_EXTERNAL)
 437                         __bump_priority(signal, __NO_PREEMPTION);
 438
 439                 ret = true;
 440         }
 441
 442         spin_unlock_irq(&schedule_lock);
 443
 444         return ret;
 445 }
 446
 447 int i915_sched_node_add_dependency(struct i915_sched_node *node,
 448                                    struct i915_sched_node *signal)
 449 {
 450         struct i915_dependency *dep;
 451
 452         dep = i915_dependency_alloc();
 453         if (!dep)
 454                 return -ENOMEM;
 455
 456         if (!__i915_sched_node_add_dependency(node, signal, dep,
 457                                               I915_DEPENDENCY_EXTERNAL |
 458                                               I915_DEPENDENCY_ALLOC))
 459                 i915_dependency_free(dep);
 460
 461         return 0;
 462 }
 463
 464 void i915_sched_node_fini(struct i915_sched_node *node)
 465 {
 466         struct i915_dependency *dep, *tmp;
 467
 468         spin_lock_irq(&schedule_lock);
 469
 470         /*
 471          * Everyone we depended upon (the fences we wait to be signaled)
 472          * should retire before us and remove themselves from our list.
 473          * However, retirement is run independently on each timeline and
 474          * so we may be called out-of-order.
 475          */
 476         list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
 477                 GEM_BUG_ON(!node_signaled(dep->signaler));
 478                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 479
 480                 list_del(&dep->wait_link);
 481                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 482                         i915_dependency_free(dep);
 483         }
 484
 485         /* Remove ourselves from everyone who depends upon us */
 486         list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
 487                 GEM_BUG_ON(dep->signaler != node);
 488                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 489
 490                 list_del(&dep->signal_link);
 491                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 492                         i915_dependency_free(dep);
 493         }
 494
 495         spin_unlock_irq(&schedule_lock);
 496 }
 497
 498 static void i915_global_scheduler_shrink(void)
 499 {
 500         kmem_cache_shrink(global.slab_dependencies);
 501         kmem_cache_shrink(global.slab_priorities);
 502 }
 503
 504 static void i915_global_scheduler_exit(void)
 505 {
 506         kmem_cache_destroy(global.slab_dependencies);
 507         kmem_cache_destroy(global.slab_priorities);
 508 }
 509
 510 static struct i915_global_scheduler global = { {
 511         .shrink = i915_global_scheduler_shrink,
 512         .exit = i915_global_scheduler_exit,
 513 } };
 514
 515 int __init i915_global_scheduler_init(void)
 516 {
 517         global.slab_dependencies = KMEM_CACHE(i915_dependency,
 518                                               SLAB_HWCACHE_ALIGN);
 519         if (!global.slab_dependencies)
 520                 return -ENOMEM;
 521
 522         global.slab_priorities = KMEM_CACHE(i915_priolist,
 523                                             SLAB_HWCACHE_ALIGN);
 524         if (!global.slab_priorities)
 525                 goto err_priorities;
 526
 527         i915_global_register(&global.base);
 528         return 0;
 529
 530 err_priorities:
 531         kmem_cache_destroy(global.slab_priorities);
 532         return -ENOMEM;
 533 }