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 }
568