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         engine->execlists.queue_priority_hint = prio;
 213
 214         /*
 215          * If we are already the currently executing context, don't
 216          * bother evaluating if we should preempt ourselves.
 217          */
 218         if (inflight->context == rq->context)
 219                 goto unlock;
 220
 221         if (need_preempt(prio, rq_prio(inflight)))
 222                 tasklet_hi_schedule(&engine->execlists.tasklet);
 223
 224 unlock:
 225         rcu_read_unlock();
 226 }
 227
 228 static void __i915_schedule(struct i915_sched_node *node,
 229                             const struct i915_sched_attr *attr)
 230 {
 231         const int prio = max(attr->priority, node->attr.priority);
 232         struct intel_engine_cs *engine;
 233         struct i915_dependency *dep, *p;
 234         struct i915_dependency stack;
 235         struct sched_cache cache;
 236         LIST_HEAD(dfs);
 237
 238         /* Needed in order to use the temporary link inside i915_dependency */
 239         lockdep_assert_held(&schedule_lock);
 240         GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
 241
 242         if (node_signaled(node))
 243                 return;
 244
 245         stack.signaler = node;
 246         list_add(&stack.dfs_link, &dfs);
 247
 248         /*
 249          * Recursively bump all dependent priorities to match the new request.
 250          *
 251          * A naive approach would be to use recursion:
 252          * static void update_priorities(struct i915_sched_node *node, prio) {
 253          *      list_for_each_entry(dep, &node->signalers_list, signal_link)
 254          *              update_priorities(dep->signal, prio)
 255          *      queue_request(node);
 256          * }
 257          * but that may have unlimited recursion depth and so runs a very
 258          * real risk of overunning the kernel stack. Instead, we build
 259          * a flat list of all dependencies starting with the current request.
 260          * As we walk the list of dependencies, we add all of its dependencies
 261          * to the end of the list (this may include an already visited
 262          * request) and continue to walk onwards onto the new dependencies. The
 263          * end result is a topological list of requests in reverse order, the
 264          * last element in the list is the request we must execute first.
 265          */
 266         list_for_each_entry(dep, &dfs, dfs_link) {
 267                 struct i915_sched_node *node = dep->signaler;
 268
 269                 /* If we are already flying, we know we have no signalers */
 270                 if (node_started(node))
 271                         continue;
 272
 273                 /*
 274                  * Within an engine, there can be no cycle, but we may
 275                  * refer to the same dependency chain multiple times
 276                  * (redundant dependencies are not eliminated) and across
 277                  * engines.
 278                  */
 279                 list_for_each_entry(p, &node->signalers_list, signal_link) {
 280                         GEM_BUG_ON(p == dep); /* no cycles! */
 281
 282                         if (node_signaled(p->signaler))
 283                                 continue;
 284
 285                         if (prio > READ_ONCE(p->signaler->attr.priority))
 286                                 list_move_tail(&p->dfs_link, &dfs);
 287                 }
 288         }
 289
 290         /*
 291          * If we didn't need to bump any existing priorities, and we haven't
 292          * yet submitted this request (i.e. there is no potential race with
 293          * execlists_submit_request()), we can set our own priority and skip
 294          * acquiring the engine locks.
 295          */
 296         if (node->attr.priority == I915_PRIORITY_INVALID) {
 297                 GEM_BUG_ON(!list_empty(&node->link));
 298                 node->attr = *attr;
 299
 300                 if (stack.dfs_link.next == stack.dfs_link.prev)
 301                         return;
 302
 303                 __list_del_entry(&stack.dfs_link);
 304         }
 305
 306         memset(&cache, 0, sizeof(cache));
 307         engine = node_to_request(node)->engine;
 308         spin_lock(&engine->active.lock);
 309
 310         /* Fifo and depth-first replacement ensure our deps execute before us */
 311         engine = sched_lock_engine(node, engine, &cache);
 312         list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
 313                 INIT_LIST_HEAD(&dep->dfs_link);
 314
 315                 node = dep->signaler;
 316                 engine = sched_lock_engine(node, engine, &cache);
 317                 lockdep_assert_held(&engine->active.lock);
 318
 319                 /* Recheck after acquiring the engine->timeline.lock */
 320                 if (prio <= node->attr.priority || node_signaled(node))
 321                         continue;
 322
 323                 GEM_BUG_ON(node_to_request(node)->engine != engine);
 324
 325                 WRITE_ONCE(node->attr.priority, prio);
 326
 327                 /*
 328                  * Once the request is ready, it will be placed into the
 329                  * priority lists and then onto the HW runlist. Before the
 330                  * request is ready, it does not contribute to our preemption
 331                  * decisions and we can safely ignore it, as it will, and
 332                  * any preemption required, be dealt with upon submission.
 333                  * See engine->submit_request()
 334                  */
 335                 if (list_empty(&node->link))
 336                         continue;
 337
 338                 if (i915_request_in_priority_queue(node_to_request(node))) {
 339                         if (!cache.priolist)
 340                                 cache.priolist =
 341                                         i915_sched_lookup_priolist(engine,
 342                                                                    prio);
 343                         list_move_tail(&node->link, cache.priolist);
 344                 }
 345
 346                 /* Defer (tasklet) submission until after all of our updates. */
 347                 kick_submission(engine, node_to_request(node), prio);
 348         }
 349
 350         spin_unlock(&engine->active.lock);
 351 }
 352
 353 void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
 354 {
 355         spin_lock_irq(&schedule_lock);
 356         __i915_schedule(&rq->sched, attr);
 357         spin_unlock_irq(&schedule_lock);
 358 }
 359
 360 static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
 361 {
 362         struct i915_sched_attr attr = node->attr;
 363
 364         if (attr.priority & bump)
 365                 return;
 366
 367         attr.priority |= bump;
 368         __i915_schedule(node, &attr);
 369 }
 370
 371 void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
 372 {
 373         unsigned long flags;
 374
 375         GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
 376         if (READ_ONCE(rq->sched.attr.priority) & bump)
 377                 return;
 378
 379         spin_lock_irqsave(&schedule_lock, flags);
 380         __bump_priority(&rq->sched, bump);
 381         spin_unlock_irqrestore(&schedule_lock, flags);
 382 }
 383
 384 void i915_sched_node_init(struct i915_sched_node *node)
 385 {
 386         INIT_LIST_HEAD(&node->signalers_list);
 387         INIT_LIST_HEAD(&node->waiters_list);
 388         INIT_LIST_HEAD(&node->link);
 389
 390         i915_sched_node_reinit(node);
 391 }
 392
 393 void i915_sched_node_reinit(struct i915_sched_node *node)
 394 {
 395         node->attr.priority = I915_PRIORITY_INVALID;
 396         node->semaphores = 0;
 397         node->flags = 0;
 398
 399         GEM_BUG_ON(!list_empty(&node->signalers_list));
 400         GEM_BUG_ON(!list_empty(&node->waiters_list));
 401         GEM_BUG_ON(!list_empty(&node->link));
 402 }
 403
 404 static struct i915_dependency *
 405 i915_dependency_alloc(void)
 406 {
 407         return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
 408 }
 409
 410 static void
 411 i915_dependency_free(struct i915_dependency *dep)
 412 {
 413         kmem_cache_free(global.slab_dependencies, dep);
 414 }
 415
 416 bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
 417                                       struct i915_sched_node *signal,
 418                                       struct i915_dependency *dep,
 419                                       unsigned long flags)
 420 {
 421         bool ret = false;
 422
 423         spin_lock_irq(&schedule_lock);
 424
 425         if (!node_signaled(signal)) {
 426                 INIT_LIST_HEAD(&dep->dfs_link);
 427                 dep->signaler = signal;
 428                 dep->waiter = node;
 429                 dep->flags = flags;
 430
 431                 /* Keep track of whether anyone on this chain has a semaphore */
 432                 if (signal->flags & I915_SCHED_HAS_SEMAPHORE_CHAIN &&
 433                     !node_started(signal))
 434                         node->flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;
 435
 436                 /* All set, now publish. Beware the lockless walkers. */
 437                 list_add_rcu(&dep->signal_link, &node->signalers_list);
 438                 list_add_rcu(&dep->wait_link, &signal->waiters_list);
 439
 440                 /*
 441                  * As we do not allow WAIT to preempt inflight requests,
 442                  * once we have executed a request, along with triggering
 443                  * any execution callbacks, we must preserve its ordering
 444                  * within the non-preemptible FIFO.
 445                  */
 446                 BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
 447                 if (flags & I915_DEPENDENCY_EXTERNAL)
 448                         __bump_priority(signal, __NO_PREEMPTION);
 449
 450                 ret = true;
 451         }
 452
 453         spin_unlock_irq(&schedule_lock);
 454
 455         return ret;
 456 }
 457
 458 int i915_sched_node_add_dependency(struct i915_sched_node *node,
 459                                    struct i915_sched_node *signal,
 460                                    unsigned long flags)
 461 {
 462         struct i915_dependency *dep;
 463
 464         dep = i915_dependency_alloc();
 465         if (!dep)
 466                 return -ENOMEM;
 467
 468         if (!__i915_sched_node_add_dependency(node, signal, dep,
 469                                               flags | I915_DEPENDENCY_ALLOC))
 470                 i915_dependency_free(dep);
 471
 472         return 0;
 473 }
 474
 475 void i915_sched_node_fini(struct i915_sched_node *node)
 476 {
 477         struct i915_dependency *dep, *tmp;
 478
 479         spin_lock_irq(&schedule_lock);
 480
 481         /*
 482          * Everyone we depended upon (the fences we wait to be signaled)
 483          * should retire before us and remove themselves from our list.
 484          * However, retirement is run independently on each timeline and
 485          * so we may be called out-of-order.
 486          */
 487         list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
 488                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 489
 490                 list_del_rcu(&dep->wait_link);
 491                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 492                         i915_dependency_free(dep);
 493         }
 494         INIT_LIST_HEAD(&node->signalers_list);
 495
 496         /* Remove ourselves from everyone who depends upon us */
 497         list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
 498                 GEM_BUG_ON(dep->signaler != node);
 499                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 500
 501                 list_del_rcu(&dep->signal_link);
 502                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 503                         i915_dependency_free(dep);
 504         }
 505         INIT_LIST_HEAD(&node->waiters_list);
 506
 507         spin_unlock_irq(&schedule_lock);
 508 }
 509
 510 static void i915_global_scheduler_shrink(void)
 511 {
 512         kmem_cache_shrink(global.slab_dependencies);
 513         kmem_cache_shrink(global.slab_priorities);
 514 }
 515
 516 static void i915_global_scheduler_exit(void)
 517 {
 518         kmem_cache_destroy(global.slab_dependencies);
 519         kmem_cache_destroy(global.slab_priorities);
 520 }
 521
 522 static struct i915_global_scheduler global = { {
 523         .shrink = i915_global_scheduler_shrink,
 524         .exit = i915_global_scheduler_exit,
 525 } };
 526
 527 int __init i915_global_scheduler_init(void)
 528 {
 529         global.slab_dependencies = KMEM_CACHE(i915_dependency,
 530                                               SLAB_HWCACHE_ALIGN |
 531                                               SLAB_TYPESAFE_BY_RCU);
 532         if (!global.slab_dependencies)
 533                 return -ENOMEM;
 534
 535         global.slab_priorities = KMEM_CACHE(i915_priolist,
 536                                             SLAB_HWCACHE_ALIGN);
 537         if (!global.slab_priorities)
 538                 goto err_priorities;
 539
 540         i915_global_register(&global.base);
 541         return 0;
 542
 543 err_priorities:
 544         kmem_cache_destroy(global.slab_priorities);
 545         return -ENOMEM;
 546 }