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 i915_sched_engine * const sched_engine)
  44 {
  45         struct rb_node *rb;
  46         long last_prio;
  47
  48         if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
  49                 return;
  50
  51         GEM_BUG_ON(rb_first_cached(&sched_engine->queue) !=
  52                    rb_first(&sched_engine->queue.rb_root));
  53
  54         last_prio = INT_MAX;
  55         for (rb = rb_first_cached(&sched_engine->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 }
  62
  63 struct list_head *
  64 i915_sched_lookup_priolist(struct i915_sched_engine *sched_engine, int prio)
  65 {
  66         struct i915_priolist *p;
  67         struct rb_node **parent, *rb;
  68         bool first = true;
  69
  70         lockdep_assert_held(&sched_engine->lock);
  71         assert_priolists(sched_engine);
  72
  73         if (unlikely(sched_engine->no_priolist))
  74                 prio = I915_PRIORITY_NORMAL;
  75
  76 find_priolist:
  77         /* most positive priority is scheduled first, equal priorities fifo */
  78         rb = NULL;
  79         parent = &sched_engine->queue.rb_root.rb_node;
  80         while (*parent) {
  81                 rb = *parent;
  82                 p = to_priolist(rb);
  83                 if (prio > p->priority) {
  84                         parent = &rb->rb_left;
  85                 } else if (prio < p->priority) {
  86                         parent = &rb->rb_right;
  87                         first = false;
  88                 } else {
  89                         return &p->requests;
  90                 }
  91         }
  92
  93         if (prio == I915_PRIORITY_NORMAL) {
  94                 p = &sched_engine->default_priolist;
  95         } else {
  96                 p = kmem_cache_alloc(global.slab_priorities, GFP_ATOMIC);
  97                 /* Convert an allocation failure to a priority bump */
  98                 if (unlikely(!p)) {
  99                         prio = I915_PRIORITY_NORMAL; /* recurses just once */
 100
 101                         /* To maintain ordering with all rendering, after an
 102                          * allocation failure we have to disable all scheduling.
 103                          * Requests will then be executed in fifo, and schedule
 104                          * will ensure that dependencies are emitted in fifo.
 105                          * There will be still some reordering with existing
 106                          * requests, so if userspace lied about their
 107                          * dependencies that reordering may be visible.
 108                          */
 109                         sched_engine->no_priolist = true;
 110                         goto find_priolist;
 111                 }
 112         }
 113
 114         p->priority = prio;
 115         INIT_LIST_HEAD(&p->requests);
 116
 117         rb_link_node(&p->node, rb, parent);
 118         rb_insert_color_cached(&p->node, &sched_engine->queue, first);
 119
 120         return &p->requests;
 121 }
 122
 123 void __i915_priolist_free(struct i915_priolist *p)
 124 {
 125         kmem_cache_free(global.slab_priorities, p);
 126 }
 127
 128 struct sched_cache {
 129         struct list_head *priolist;
 130 };
 131
 132 static struct i915_sched_engine *
 133 lock_sched_engine(struct i915_sched_node *node,
 134                   struct i915_sched_engine *locked,
 135                   struct sched_cache *cache)
 136 {
 137         const struct i915_request *rq = node_to_request(node);
 138         struct i915_sched_engine *sched_engine;
 139
 140         GEM_BUG_ON(!locked);
 141
 142         /*
 143          * Virtual engines complicate acquiring the engine timeline lock,
 144          * as their rq->engine pointer is not stable until under that
 145          * engine lock. The simple ploy we use is to take the lock then
 146          * check that the rq still belongs to the newly locked engine.
 147          */
 148         while (locked != (sched_engine = READ_ONCE(rq->engine)->sched_engine)) {
 149                 spin_unlock(&locked->lock);
 150                 memset(cache, 0, sizeof(*cache));
 151                 spin_lock(&sched_engine->lock);
 152                 locked = sched_engine;
 153         }
 154
 155         GEM_BUG_ON(locked != sched_engine);
 156         return locked;
 157 }
 158
 159 static void __i915_schedule(struct i915_sched_node *node,
 160                             const struct i915_sched_attr *attr)
 161 {
 162         const int prio = max(attr->priority, node->attr.priority);
 163         struct i915_sched_engine *sched_engine;
 164         struct i915_dependency *dep, *p;
 165         struct i915_dependency stack;
 166         struct sched_cache cache;
 167         LIST_HEAD(dfs);
 168
 169         /* Needed in order to use the temporary link inside i915_dependency */
 170         lockdep_assert_held(&schedule_lock);
 171         GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
 172
 173         if (node_signaled(node))
 174                 return;
 175
 176         stack.signaler = node;
 177         list_add(&stack.dfs_link, &dfs);
 178
 179         /*
 180          * Recursively bump all dependent priorities to match the new request.
 181          *
 182          * A naive approach would be to use recursion:
 183          * static void update_priorities(struct i915_sched_node *node, prio) {
 184          *      list_for_each_entry(dep, &node->signalers_list, signal_link)
 185          *              update_priorities(dep->signal, prio)
 186          *      queue_request(node);
 187          * }
 188          * but that may have unlimited recursion depth and so runs a very
 189          * real risk of overunning the kernel stack. Instead, we build
 190          * a flat list of all dependencies starting with the current request.
 191          * As we walk the list of dependencies, we add all of its dependencies
 192          * to the end of the list (this may include an already visited
 193          * request) and continue to walk onwards onto the new dependencies. The
 194          * end result is a topological list of requests in reverse order, the
 195          * last element in the list is the request we must execute first.
 196          */
 197         list_for_each_entry(dep, &dfs, dfs_link) {
 198                 struct i915_sched_node *node = dep->signaler;
 199
 200                 /* If we are already flying, we know we have no signalers */
 201                 if (node_started(node))
 202                         continue;
 203
 204                 /*
 205                  * Within an engine, there can be no cycle, but we may
 206                  * refer to the same dependency chain multiple times
 207                  * (redundant dependencies are not eliminated) and across
 208                  * engines.
 209                  */
 210                 list_for_each_entry(p, &node->signalers_list, signal_link) {
 211                         GEM_BUG_ON(p == dep); /* no cycles! */
 212
 213                         if (node_signaled(p->signaler))
 214                                 continue;
 215
 216                         if (prio > READ_ONCE(p->signaler->attr.priority))
 217                                 list_move_tail(&p->dfs_link, &dfs);
 218                 }
 219         }
 220
 221         /*
 222          * If we didn't need to bump any existing priorities, and we haven't
 223          * yet submitted this request (i.e. there is no potential race with
 224          * execlists_submit_request()), we can set our own priority and skip
 225          * acquiring the engine locks.
 226          */
 227         if (node->attr.priority == I915_PRIORITY_INVALID) {
 228                 GEM_BUG_ON(!list_empty(&node->link));
 229                 node->attr = *attr;
 230
 231                 if (stack.dfs_link.next == stack.dfs_link.prev)
 232                         return;
 233
 234                 __list_del_entry(&stack.dfs_link);
 235         }
 236
 237         memset(&cache, 0, sizeof(cache));
 238         sched_engine = node_to_request(node)->engine->sched_engine;
 239         spin_lock(&sched_engine->lock);
 240
 241         /* Fifo and depth-first replacement ensure our deps execute before us */
 242         sched_engine = lock_sched_engine(node, sched_engine, &cache);
 243         list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
 244                 INIT_LIST_HEAD(&dep->dfs_link);
 245
 246                 node = dep->signaler;
 247                 sched_engine = lock_sched_engine(node, sched_engine, &cache);
 248                 lockdep_assert_held(&sched_engine->lock);
 249
 250                 /* Recheck after acquiring the engine->timeline.lock */
 251                 if (prio <= node->attr.priority || node_signaled(node))
 252                         continue;
 253
 254                 GEM_BUG_ON(node_to_request(node)->engine->sched_engine !=
 255                            sched_engine);
 256
 257                 WRITE_ONCE(node->attr.priority, prio);
 258
 259                 /*
 260                  * Once the request is ready, it will be placed into the
 261                  * priority lists and then onto the HW runlist. Before the
 262                  * request is ready, it does not contribute to our preemption
 263                  * decisions and we can safely ignore it, as it will, and
 264                  * any preemption required, be dealt with upon submission.
 265                  * See engine->submit_request()
 266                  */
 267                 if (list_empty(&node->link))
 268                         continue;
 269
 270                 if (i915_request_in_priority_queue(node_to_request(node))) {
 271                         if (!cache.priolist)
 272                                 cache.priolist =
 273                                         i915_sched_lookup_priolist(sched_engine,
 274                                                                    prio);
 275                         list_move_tail(&node->link, cache.priolist);
 276                 }
 277
 278                 /* Defer (tasklet) submission until after all of our updates. */
 279                 if (sched_engine->kick_backend)
 280                         sched_engine->kick_backend(node_to_request(node), prio);
 281         }
 282
 283         spin_unlock(&sched_engine->lock);
 284 }
 285
 286 void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
 287 {
 288         spin_lock_irq(&schedule_lock);
 289         __i915_schedule(&rq->sched, attr);
 290         spin_unlock_irq(&schedule_lock);
 291 }
 292
 293 void i915_sched_node_init(struct i915_sched_node *node)
 294 {
 295         INIT_LIST_HEAD(&node->signalers_list);
 296         INIT_LIST_HEAD(&node->waiters_list);
 297         INIT_LIST_HEAD(&node->link);
 298
 299         i915_sched_node_reinit(node);
 300 }
 301
 302 void i915_sched_node_reinit(struct i915_sched_node *node)
 303 {
 304         node->attr.priority = I915_PRIORITY_INVALID;
 305         node->semaphores = 0;
 306         node->flags = 0;
 307
 308         GEM_BUG_ON(!list_empty(&node->signalers_list));
 309         GEM_BUG_ON(!list_empty(&node->waiters_list));
 310         GEM_BUG_ON(!list_empty(&node->link));
 311 }
 312
 313 static struct i915_dependency *
 314 i915_dependency_alloc(void)
 315 {
 316         return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
 317 }
 318
 319 static void
 320 i915_dependency_free(struct i915_dependency *dep)
 321 {
 322         kmem_cache_free(global.slab_dependencies, dep);
 323 }
 324
 325 bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
 326                                       struct i915_sched_node *signal,
 327                                       struct i915_dependency *dep,
 328                                       unsigned long flags)
 329 {
 330         bool ret = false;
 331
 332         spin_lock_irq(&schedule_lock);
 333
 334         if (!node_signaled(signal)) {
 335                 INIT_LIST_HEAD(&dep->dfs_link);
 336                 dep->signaler = signal;
 337                 dep->waiter = node;
 338                 dep->flags = flags;
 339
 340                 /* All set, now publish. Beware the lockless walkers. */
 341                 list_add_rcu(&dep->signal_link, &node->signalers_list);
 342                 list_add_rcu(&dep->wait_link, &signal->waiters_list);
 343
 344                 /* Propagate the chains */
 345                 node->flags |= signal->flags;
 346                 ret = true;
 347         }
 348
 349         spin_unlock_irq(&schedule_lock);
 350
 351         return ret;
 352 }
 353
 354 int i915_sched_node_add_dependency(struct i915_sched_node *node,
 355                                    struct i915_sched_node *signal,
 356                                    unsigned long flags)
 357 {
 358         struct i915_dependency *dep;
 359
 360         dep = i915_dependency_alloc();
 361         if (!dep)
 362                 return -ENOMEM;
 363
 364         if (!__i915_sched_node_add_dependency(node, signal, dep,
 365                                               flags | I915_DEPENDENCY_ALLOC))
 366                 i915_dependency_free(dep);
 367
 368         return 0;
 369 }
 370
 371 void i915_sched_node_fini(struct i915_sched_node *node)
 372 {
 373         struct i915_dependency *dep, *tmp;
 374
 375         spin_lock_irq(&schedule_lock);
 376
 377         /*
 378          * Everyone we depended upon (the fences we wait to be signaled)
 379          * should retire before us and remove themselves from our list.
 380          * However, retirement is run independently on each timeline and
 381          * so we may be called out-of-order.
 382          */
 383         list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
 384                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 385
 386                 list_del_rcu(&dep->wait_link);
 387                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 388                         i915_dependency_free(dep);
 389         }
 390         INIT_LIST_HEAD(&node->signalers_list);
 391
 392         /* Remove ourselves from everyone who depends upon us */
 393         list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
 394                 GEM_BUG_ON(dep->signaler != node);
 395                 GEM_BUG_ON(!list_empty(&dep->dfs_link));
 396
 397                 list_del_rcu(&dep->signal_link);
 398                 if (dep->flags & I915_DEPENDENCY_ALLOC)
 399                         i915_dependency_free(dep);
 400         }
 401         INIT_LIST_HEAD(&node->waiters_list);
 402
 403         spin_unlock_irq(&schedule_lock);
 404 }
 405
 406 void i915_request_show_with_schedule(struct drm_printer *m,
 407                                      const struct i915_request *rq,
 408                                      const char *prefix,
 409                                      int indent)
 410 {
 411         struct i915_dependency *dep;
 412
 413         i915_request_show(m, rq, prefix, indent);
 414         if (i915_request_completed(rq))
 415                 return;
 416
 417         rcu_read_lock();
 418         for_each_signaler(dep, rq) {
 419                 const struct i915_request *signaler =
 420                         node_to_request(dep->signaler);
 421
 422                 /* Dependencies along the same timeline are expected. */
 423                 if (signaler->timeline == rq->timeline)
 424                         continue;
 425
 426                 if (__i915_request_is_complete(signaler))
 427                         continue;
 428
 429                 i915_request_show(m, signaler, prefix, indent + 2);
 430         }
 431         rcu_read_unlock();
 432 }
 433
 434 void i915_sched_engine_free(struct kref *kref)
 435 {
 436         struct i915_sched_engine *sched_engine =
 437                 container_of(kref, typeof(*sched_engine), ref);
 438
 439         tasklet_kill(&sched_engine->tasklet); /* flush the callback */
 440         kfree(sched_engine);
 441 }
 442
 443 struct i915_sched_engine *
 444 i915_sched_engine_create(unsigned int subclass)
 445 {
 446         struct i915_sched_engine *sched_engine;
 447
 448         sched_engine = kzalloc(sizeof(*sched_engine), GFP_KERNEL);
 449         if (!sched_engine)
 450                 return NULL;
 451
 452         kref_init(&sched_engine->ref);
 453
 454         sched_engine->queue = RB_ROOT_CACHED;
 455         sched_engine->queue_priority_hint = INT_MIN;
 456
 457         INIT_LIST_HEAD(&sched_engine->requests);
 458         INIT_LIST_HEAD(&sched_engine->hold);
 459
 460         spin_lock_init(&sched_engine->lock);
 461         lockdep_set_subclass(&sched_engine->lock, subclass);
 462
 463         /*
 464          * Due to an interesting quirk in lockdep's internal debug tracking,
 465          * after setting a subclass we must ensure the lock is used. Otherwise,
 466          * nr_unused_locks is incremented once too often.
 467          */
 468 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 469         local_irq_disable();
 470         lock_map_acquire(&sched_engine->lock.dep_map);
 471         lock_map_release(&sched_engine->lock.dep_map);
 472         local_irq_enable();
 473 #endif
 474
 475         return sched_engine;
 476 }
 477
 478 static void i915_global_scheduler_exit(void)
 479 {
 480         kmem_cache_destroy(global.slab_dependencies);
 481         kmem_cache_destroy(global.slab_priorities);
 482 }
 483
 484 static struct i915_global_scheduler global = { {
 485         .exit = i915_global_scheduler_exit,
 486 } };
 487
 488 int __init i915_global_scheduler_init(void)
 489 {
 490         global.slab_dependencies = KMEM_CACHE(i915_dependency,
 491                                               SLAB_HWCACHE_ALIGN |
 492                                               SLAB_TYPESAFE_BY_RCU);
 493         if (!global.slab_dependencies)
 494                 return -ENOMEM;
 495
 496         global.slab_priorities = KMEM_CACHE(i915_priolist, 0);
 497         if (!global.slab_priorities)
 498                 goto err_priorities;
 499
 500         i915_global_register(&global.base);
 501         return 0;
 502
 503 err_priorities:
 504         kmem_cache_destroy(global.slab_priorities);
 505         return -ENOMEM;
 506 }