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_request.h"
11#include "i915_scheduler.h"
12
13static struct kmem_cache *slab_dependencies;
14static struct kmem_cache *slab_priorities;
15
16static DEFINE_SPINLOCK(schedule_lock);
17
18static const struct i915_request *
19node_to_request(const struct i915_sched_node *node)
20{
21	return container_of(node, const struct i915_request, sched);
22}
23
24static inline bool node_started(const struct i915_sched_node *node)
25{
26	return i915_request_started(node_to_request(node));
27}
28
29static inline bool node_signaled(const struct i915_sched_node *node)
30{
31	return i915_request_completed(node_to_request(node));
32}
33
34static inline struct i915_priolist *to_priolist(struct rb_node *rb)
35{
36	return rb_entry(rb, struct i915_priolist, node);
37}
38
39static void assert_priolists(struct i915_sched_engine * const sched_engine)
40{
41	struct rb_node *rb;
42	long last_prio;
43
44	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
45		return;
46
47	GEM_BUG_ON(rb_first_cached(&sched_engine->queue) !=
48		   rb_first(&sched_engine->queue.rb_root));
49
50	last_prio = INT_MAX;
51	for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
52		const struct i915_priolist *p = to_priolist(rb);
53
54		GEM_BUG_ON(p->priority > last_prio);
55		last_prio = p->priority;
56	}
57}
58
59struct list_head *
60i915_sched_lookup_priolist(struct i915_sched_engine *sched_engine, int prio)
61{
62	struct i915_priolist *p;
63	struct rb_node **parent, *rb;
64	bool first = true;
65
66	lockdep_assert_held(&sched_engine->lock);
67	assert_priolists(sched_engine);
68
69	if (unlikely(sched_engine->no_priolist))
70		prio = I915_PRIORITY_NORMAL;
71
72find_priolist:
73	/* most positive priority is scheduled first, equal priorities fifo */
74	rb = NULL;
75	parent = &sched_engine->queue.rb_root.rb_node;
76	while (*parent) {
77		rb = *parent;
78		p = to_priolist(rb);
79		if (prio > p->priority) {
80			parent = &rb->rb_left;
81		} else if (prio < p->priority) {
82			parent = &rb->rb_right;
83			first = false;
84		} else {
85			return &p->requests;
86		}
87	}
88
89	if (prio == I915_PRIORITY_NORMAL) {
90		p = &sched_engine->default_priolist;
91	} else {
92		p = kmem_cache_alloc(slab_priorities, GFP_ATOMIC);
93		/* Convert an allocation failure to a priority bump */
94		if (unlikely(!p)) {
95			prio = I915_PRIORITY_NORMAL; /* recurses just once */
96
97			/* To maintain ordering with all rendering, after an
98			 * allocation failure we have to disable all scheduling.
99			 * Requests will then be executed in fifo, and schedule
100			 * will ensure that dependencies are emitted in fifo.
101			 * There will be still some reordering with existing
102			 * requests, so if userspace lied about their
103			 * dependencies that reordering may be visible.
104			 */
105			sched_engine->no_priolist = true;
106			goto find_priolist;
107		}
108	}
109
110	p->priority = prio;
111	INIT_LIST_HEAD(&p->requests);
112
113	rb_link_node(&p->node, rb, parent);
114	rb_insert_color_cached(&p->node, &sched_engine->queue, first);
115
116	return &p->requests;
117}
118
119void __i915_priolist_free(struct i915_priolist *p)
120{
121	kmem_cache_free(slab_priorities, p);
122}
123
124struct sched_cache {
125	struct list_head *priolist;
126};
127
128static struct i915_sched_engine *
129lock_sched_engine(struct i915_sched_node *node,
130		  struct i915_sched_engine *locked,
131		  struct sched_cache *cache)
132{
133	const struct i915_request *rq = node_to_request(node);
134	struct i915_sched_engine *sched_engine;
135
136	GEM_BUG_ON(!locked);
137
138	/*
139	 * Virtual engines complicate acquiring the engine timeline lock,
140	 * as their rq->engine pointer is not stable until under that
141	 * engine lock. The simple ploy we use is to take the lock then
142	 * check that the rq still belongs to the newly locked engine.
143	 */
144	while (locked != (sched_engine = READ_ONCE(rq->engine)->sched_engine)) {
145		spin_unlock(&locked->lock);
146		memset(cache, 0, sizeof(*cache));
147		spin_lock(&sched_engine->lock);
148		locked = sched_engine;
149	}
150
151	GEM_BUG_ON(locked != sched_engine);
152	return locked;
153}
154
155static void __i915_schedule(struct i915_sched_node *node,
156			    const struct i915_sched_attr *attr)
157{
158	const int prio = max(attr->priority, node->attr.priority);
159	struct i915_sched_engine *sched_engine;
160	struct i915_dependency *dep, *p;
161	struct i915_dependency stack;
162	struct sched_cache cache;
163	LIST_HEAD(dfs);
164
165	/* Needed in order to use the temporary link inside i915_dependency */
166	lockdep_assert_held(&schedule_lock);
167	GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
168
169	if (node_signaled(node))
170		return;
171
172	stack.signaler = node;
173	list_add(&stack.dfs_link, &dfs);
174
175	/*
176	 * Recursively bump all dependent priorities to match the new request.
177	 *
178	 * A naive approach would be to use recursion:
179	 * static void update_priorities(struct i915_sched_node *node, prio) {
180	 *	list_for_each_entry(dep, &node->signalers_list, signal_link)
181	 *		update_priorities(dep->signal, prio)
182	 *	queue_request(node);
183	 * }
184	 * but that may have unlimited recursion depth and so runs a very
185	 * real risk of overunning the kernel stack. Instead, we build
186	 * a flat list of all dependencies starting with the current request.
187	 * As we walk the list of dependencies, we add all of its dependencies
188	 * to the end of the list (this may include an already visited
189	 * request) and continue to walk onwards onto the new dependencies. The
190	 * end result is a topological list of requests in reverse order, the
191	 * last element in the list is the request we must execute first.
192	 */
193	list_for_each_entry(dep, &dfs, dfs_link) {
194		struct i915_sched_node *node = dep->signaler;
195
196		/* If we are already flying, we know we have no signalers */
197		if (node_started(node))
198			continue;
199
200		/*
201		 * Within an engine, there can be no cycle, but we may
202		 * refer to the same dependency chain multiple times
203		 * (redundant dependencies are not eliminated) and across
204		 * engines.
205		 */
206		list_for_each_entry(p, &node->signalers_list, signal_link) {
207			GEM_BUG_ON(p == dep); /* no cycles! */
208
209			if (node_signaled(p->signaler))
210				continue;
211
212			if (prio > READ_ONCE(p->signaler->attr.priority))
213				list_move_tail(&p->dfs_link, &dfs);
214		}
215	}
216
217	/*
218	 * If we didn't need to bump any existing priorities, and we haven't
219	 * yet submitted this request (i.e. there is no potential race with
220	 * execlists_submit_request()), we can set our own priority and skip
221	 * acquiring the engine locks.
222	 */
223	if (node->attr.priority == I915_PRIORITY_INVALID) {
224		GEM_BUG_ON(!list_empty(&node->link));
225		node->attr = *attr;
226
227		if (stack.dfs_link.next == stack.dfs_link.prev)
228			return;
229
230		__list_del_entry(&stack.dfs_link);
231	}
232
233	memset(&cache, 0, sizeof(cache));
234	sched_engine = node_to_request(node)->engine->sched_engine;
235	spin_lock(&sched_engine->lock);
236
237	/* Fifo and depth-first replacement ensure our deps execute before us */
238	sched_engine = lock_sched_engine(node, sched_engine, &cache);
239	list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
240		struct i915_request *from = container_of(dep->signaler,
241							 struct i915_request,
242							 sched);
243		INIT_LIST_HEAD(&dep->dfs_link);
244
245		node = dep->signaler;
246		sched_engine = lock_sched_engine(node, sched_engine, &cache);
247		lockdep_assert_held(&sched_engine->lock);
248
249		/* Recheck after acquiring the engine->timeline.lock */
250		if (prio <= node->attr.priority || node_signaled(node))
251			continue;
252
253		GEM_BUG_ON(node_to_request(node)->engine->sched_engine !=
254			   sched_engine);
255
256		/* Must be called before changing the nodes priority */
257		if (sched_engine->bump_inflight_request_prio)
258			sched_engine->bump_inflight_request_prio(from, prio);
259
260		WRITE_ONCE(node->attr.priority, prio);
261
262		/*
263		 * Once the request is ready, it will be placed into the
264		 * priority lists and then onto the HW runlist. Before the
265		 * request is ready, it does not contribute to our preemption
266		 * decisions and we can safely ignore it, as it will, and
267		 * any preemption required, be dealt with upon submission.
268		 * See engine->submit_request()
269		 */
270		if (list_empty(&node->link))
271			continue;
272
273		if (i915_request_in_priority_queue(node_to_request(node))) {
274			if (!cache.priolist)
275				cache.priolist =
276					i915_sched_lookup_priolist(sched_engine,
277								   prio);
278			list_move_tail(&node->link, cache.priolist);
279		}
280
281		/* Defer (tasklet) submission until after all of our updates. */
282		if (sched_engine->kick_backend)
283			sched_engine->kick_backend(node_to_request(node), prio);
284	}
285
286	spin_unlock(&sched_engine->lock);
287}
288
289void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
290{
291	spin_lock_irq(&schedule_lock);
292	__i915_schedule(&rq->sched, attr);
293	spin_unlock_irq(&schedule_lock);
294}
295
296void i915_sched_node_init(struct i915_sched_node *node)
297{
298	INIT_LIST_HEAD(&node->signalers_list);
299	INIT_LIST_HEAD(&node->waiters_list);
300	INIT_LIST_HEAD(&node->link);
301
302	i915_sched_node_reinit(node);
303}
304
305void i915_sched_node_reinit(struct i915_sched_node *node)
306{
307	node->attr.priority = I915_PRIORITY_INVALID;
308	node->semaphores = 0;
309	node->flags = 0;
310
311	GEM_BUG_ON(!list_empty(&node->signalers_list));
312	GEM_BUG_ON(!list_empty(&node->waiters_list));
313	GEM_BUG_ON(!list_empty(&node->link));
314}
315
316static struct i915_dependency *
317i915_dependency_alloc(void)
318{
319	return kmem_cache_alloc(slab_dependencies, GFP_KERNEL);
320}
321
322static void
323i915_dependency_free(struct i915_dependency *dep)
324{
325	kmem_cache_free(slab_dependencies, dep);
326}
327
328bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
329				      struct i915_sched_node *signal,
330				      struct i915_dependency *dep,
331				      unsigned long flags)
332{
333	bool ret = false;
334
335	spin_lock_irq(&schedule_lock);
336
337	if (!node_signaled(signal)) {
338		INIT_LIST_HEAD(&dep->dfs_link);
339		dep->signaler = signal;
340		dep->waiter = node;
341		dep->flags = flags;
342
343		/* All set, now publish. Beware the lockless walkers. */
344		list_add_rcu(&dep->signal_link, &node->signalers_list);
345		list_add_rcu(&dep->wait_link, &signal->waiters_list);
346
347		/* Propagate the chains */
348		node->flags |= signal->flags;
349		ret = true;
350	}
351
352	spin_unlock_irq(&schedule_lock);
353
354	return ret;
355}
356
357int i915_sched_node_add_dependency(struct i915_sched_node *node,
358				   struct i915_sched_node *signal,
359				   unsigned long flags)
360{
361	struct i915_dependency *dep;
362
363	dep = i915_dependency_alloc();
364	if (!dep)
365		return -ENOMEM;
366
367	if (!__i915_sched_node_add_dependency(node, signal, dep,
368					      flags | I915_DEPENDENCY_ALLOC))
369		i915_dependency_free(dep);
370
371	return 0;
372}
373
374void i915_sched_node_fini(struct i915_sched_node *node)
375{
376	struct i915_dependency *dep, *tmp;
377
378	spin_lock_irq(&schedule_lock);
379
380	/*
381	 * Everyone we depended upon (the fences we wait to be signaled)
382	 * should retire before us and remove themselves from our list.
383	 * However, retirement is run independently on each timeline and
384	 * so we may be called out-of-order.
385	 */
386	list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
387		GEM_BUG_ON(!list_empty(&dep->dfs_link));
388
389		list_del_rcu(&dep->wait_link);
390		if (dep->flags & I915_DEPENDENCY_ALLOC)
391			i915_dependency_free(dep);
392	}
393	INIT_LIST_HEAD(&node->signalers_list);
394
395	/* Remove ourselves from everyone who depends upon us */
396	list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
397		GEM_BUG_ON(dep->signaler != node);
398		GEM_BUG_ON(!list_empty(&dep->dfs_link));
399
400		list_del_rcu(&dep->signal_link);
401		if (dep->flags & I915_DEPENDENCY_ALLOC)
402			i915_dependency_free(dep);
403	}
404	INIT_LIST_HEAD(&node->waiters_list);
405
406	spin_unlock_irq(&schedule_lock);
407}
408
409void i915_request_show_with_schedule(struct drm_printer *m,
410				     const struct i915_request *rq,
411				     const char *prefix,
412				     int indent)
413{
414	struct i915_dependency *dep;
415
416	i915_request_show(m, rq, prefix, indent);
417	if (i915_request_completed(rq))
418		return;
419
420	rcu_read_lock();
421	for_each_signaler(dep, rq) {
422		const struct i915_request *signaler =
423			node_to_request(dep->signaler);
424
425		/* Dependencies along the same timeline are expected. */
426		if (signaler->timeline == rq->timeline)
427			continue;
428
429		if (__i915_request_is_complete(signaler))
430			continue;
431
432		i915_request_show(m, signaler, prefix, indent + 2);
433	}
434	rcu_read_unlock();
435}
436
437static void default_destroy(struct kref *kref)
438{
439	struct i915_sched_engine *sched_engine =
440		container_of(kref, typeof(*sched_engine), ref);
441
442	tasklet_kill(&sched_engine->tasklet); /* flush the callback */
443	kfree(sched_engine);
444}
445
446static bool default_disabled(struct i915_sched_engine *sched_engine)
447{
448	return false;
449}
450
451struct i915_sched_engine *
452i915_sched_engine_create(unsigned int subclass)
453{
454	struct i915_sched_engine *sched_engine;
455
456	sched_engine = kzalloc(sizeof(*sched_engine), GFP_KERNEL);
457	if (!sched_engine)
458		return NULL;
459
460	kref_init(&sched_engine->ref);
461
462	sched_engine->queue = RB_ROOT_CACHED;
463	sched_engine->queue_priority_hint = INT_MIN;
464	sched_engine->destroy = default_destroy;
465	sched_engine->disabled = default_disabled;
466
467	INIT_LIST_HEAD(&sched_engine->requests);
468	INIT_LIST_HEAD(&sched_engine->hold);
469
470	spin_lock_init(&sched_engine->lock);
471	lockdep_set_subclass(&sched_engine->lock, subclass);
472
473	/*
474	 * Due to an interesting quirk in lockdep's internal debug tracking,
475	 * after setting a subclass we must ensure the lock is used. Otherwise,
476	 * nr_unused_locks is incremented once too often.
477	 */
478#ifdef CONFIG_DEBUG_LOCK_ALLOC
479	local_irq_disable();
480	lock_map_acquire(&sched_engine->lock.dep_map);
481	lock_map_release(&sched_engine->lock.dep_map);
482	local_irq_enable();
483#endif
484
485	return sched_engine;
486}
487
488void i915_scheduler_module_exit(void)
489{
490	kmem_cache_destroy(slab_dependencies);
491	kmem_cache_destroy(slab_priorities);
492}
493
494int __init i915_scheduler_module_init(void)
495{
496	slab_dependencies = KMEM_CACHE(i915_dependency,
497					      SLAB_HWCACHE_ALIGN |
498					      SLAB_TYPESAFE_BY_RCU);
499	if (!slab_dependencies)
500		return -ENOMEM;
501
502	slab_priorities = KMEM_CACHE(i915_priolist, 0);
503	if (!slab_priorities)
504		goto err_priorities;
505
506	return 0;
507
508err_priorities:
509	kmem_cache_destroy(slab_priorities);
510	return -ENOMEM;
511}
512