drivers/gpu/drm/i915/i915_scheduler.c - linux - Git at Google

 /*
  * SPDX-License-Identifier: MIT
  *
  * Copyright © 2018 Intel Corporation
  */

 #include <linux/mutex.h>

 #include "i915_drv.h"
 #include "i915_request.h"
 #include "i915_scheduler.h"

 static struct kmem_cache *slab_dependencies;
 static struct kmem_cache *slab_priorities;

 static DEFINE_SPINLOCK(schedule_lock);

 static const struct i915_request *
 node_to_request(const struct i915_sched_node *node)
 {
 	return container_of(node, const struct i915_request, sched);
 }

 static inline bool node_started(const struct i915_sched_node *node)
 {
 	return i915_request_started(node_to_request(node));
 }

 static inline bool node_signaled(const struct i915_sched_node *node)
 {
 	return i915_request_completed(node_to_request(node));
 }

 static inline struct i915_priolist *to_priolist(struct rb_node *rb)
 {
 	return rb_entry(rb, struct i915_priolist, node);
 }

 static void assert_priolists(struct i915_sched_engine * const sched_engine)
 {
 	struct rb_node *rb;
 	long last_prio;

 	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
 		return;

 	GEM_BUG_ON(rb_first_cached(&sched_engine->queue) !=
 		   rb_first(&sched_engine->queue.rb_root));

 	last_prio = INT_MAX;
 	for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
 		const struct i915_priolist *p = to_priolist(rb);

 		GEM_BUG_ON(p->priority > last_prio);
 		last_prio = p->priority;
 	}
 }

 struct list_head *
 i915_sched_lookup_priolist(struct i915_sched_engine *sched_engine, int prio)
 {
 	struct i915_priolist *p;
 	struct rb_node **parent, *rb;
 	bool first = true;

 	lockdep_assert_held(&sched_engine->lock);
 	assert_priolists(sched_engine);

 	if (unlikely(sched_engine->no_priolist))
 		prio = I915_PRIORITY_NORMAL;

 find_priolist:
 	/* most positive priority is scheduled first, equal priorities fifo */
 	rb = NULL;
 	parent = &sched_engine->queue.rb_root.rb_node;
 	while (*parent) {
 		rb = *parent;
 		p = to_priolist(rb);
 		if (prio > p->priority) {
 			parent = &rb->rb_left;
 		} else if (prio < p->priority) {
 			parent = &rb->rb_right;
 			first = false;
 		} else {
 			return &p->requests;
 		}
 	}

 	if (prio == I915_PRIORITY_NORMAL) {
 		p = &sched_engine->default_priolist;
 	} else {
 		p = kmem_cache_alloc(slab_priorities, GFP_ATOMIC);
 		/* Convert an allocation failure to a priority bump */
 		if (unlikely(!p)) {
 			prio = I915_PRIORITY_NORMAL; /* recurses just once */

 			/* To maintain ordering with all rendering, after an
 			 * allocation failure we have to disable all scheduling.
 			 * Requests will then be executed in fifo, and schedule
 			 * will ensure that dependencies are emitted in fifo.
 			 * There will be still some reordering with existing
 			 * requests, so if userspace lied about their
 			 * dependencies that reordering may be visible.
 			 */
 			sched_engine->no_priolist = true;
 			goto find_priolist;
 		}
 	}

 	p->priority = prio;
 	INIT_LIST_HEAD(&p->requests);

 	rb_link_node(&p->node, rb, parent);
 	rb_insert_color_cached(&p->node, &sched_engine->queue, first);

 	return &p->requests;
 }

 void __i915_priolist_free(struct i915_priolist *p)
 {
 	kmem_cache_free(slab_priorities, p);
 }

 struct sched_cache {
 	struct list_head *priolist;
 };

 static struct i915_sched_engine *
 lock_sched_engine(struct i915_sched_node *node,
 		  struct i915_sched_engine *locked,
 		  struct sched_cache *cache)
 {
 	const struct i915_request *rq = node_to_request(node);
 	struct i915_sched_engine *sched_engine;

 	GEM_BUG_ON(!locked);

 	/*
 	 * Virtual engines complicate acquiring the engine timeline lock,
 	 * as their rq->engine pointer is not stable until under that
 	 * engine lock. The simple ploy we use is to take the lock then
 	 * check that the rq still belongs to the newly locked engine.
 	 */
 	while (locked != (sched_engine = READ_ONCE(rq->engine)->sched_engine)) {
 		spin_unlock(&locked->lock);
 		memset(cache, 0, sizeof(*cache));
 		spin_lock(&sched_engine->lock);
 		locked = sched_engine;
 	}

 	GEM_BUG_ON(locked != sched_engine);
 	return locked;
 }

 static void __i915_schedule(struct i915_sched_node *node,
 			    const struct i915_sched_attr *attr)
 {
 	const int prio = max(attr->priority, node->attr.priority);
 	struct i915_sched_engine *sched_engine;
 	struct i915_dependency *dep, *p;
 	struct i915_dependency stack;
 	struct sched_cache cache;
 	LIST_HEAD(dfs);

 	/* Needed in order to use the temporary link inside i915_dependency */
 	lockdep_assert_held(&schedule_lock);
 	GEM_BUG_ON(prio == I915_PRIORITY_INVALID);

 	if (node_signaled(node))
 		return;

 	stack.signaler = node;
 	list_add(&stack.dfs_link, &dfs);

 	/*
 	 * Recursively bump all dependent priorities to match the new request.
 	 *
 	 * A naive approach would be to use recursion:
 	 * static void update_priorities(struct i915_sched_node *node, prio) {
 	 *	list_for_each_entry(dep, &node->signalers_list, signal_link)
 	 *		update_priorities(dep->signal, prio)
 	 *	queue_request(node);
 	 * }
 	 * but that may have unlimited recursion depth and so runs a very
 	 * real risk of overunning the kernel stack. Instead, we build
 	 * a flat list of all dependencies starting with the current request.
 	 * As we walk the list of dependencies, we add all of its dependencies
 	 * to the end of the list (this may include an already visited
 	 * request) and continue to walk onwards onto the new dependencies. The
 	 * end result is a topological list of requests in reverse order, the
 	 * last element in the list is the request we must execute first.
 	 */
 	list_for_each_entry(dep, &dfs, dfs_link) {
 		struct i915_sched_node *node = dep->signaler;

 		/* If we are already flying, we know we have no signalers */
 		if (node_started(node))
 			continue;

 		/*
 		 * Within an engine, there can be no cycle, but we may
 		 * refer to the same dependency chain multiple times
 		 * (redundant dependencies are not eliminated) and across
 		 * engines.
 		 */
 		list_for_each_entry(p, &node->signalers_list, signal_link) {
 			GEM_BUG_ON(p == dep); /* no cycles! */

 			if (node_signaled(p->signaler))
 				continue;

 			if (prio > READ_ONCE(p->signaler->attr.priority))
 				list_move_tail(&p->dfs_link, &dfs);
 		}
 	}

 	/*
 	 * If we didn't need to bump any existing priorities, and we haven't
 	 * yet submitted this request (i.e. there is no potential race with
 	 * execlists_submit_request()), we can set our own priority and skip
 	 * acquiring the engine locks.
 	 */
 	if (node->attr.priority == I915_PRIORITY_INVALID) {
 		GEM_BUG_ON(!list_empty(&node->link));
 		node->attr = *attr;

 		if (stack.dfs_link.next == stack.dfs_link.prev)
 			return;

 		__list_del_entry(&stack.dfs_link);
 	}

 	memset(&cache, 0, sizeof(cache));
 	sched_engine = node_to_request(node)->engine->sched_engine;
 	spin_lock(&sched_engine->lock);

 	/* Fifo and depth-first replacement ensure our deps execute before us */
 	sched_engine = lock_sched_engine(node, sched_engine, &cache);
 	list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
 		struct i915_request *from = container_of(dep->signaler,
 							 struct i915_request,
 							 sched);
 		INIT_LIST_HEAD(&dep->dfs_link);

 		node = dep->signaler;
 		sched_engine = lock_sched_engine(node, sched_engine, &cache);
 		lockdep_assert_held(&sched_engine->lock);

 		/* Recheck after acquiring the engine->timeline.lock */
 		if (prio <= node->attr.priority || node_signaled(node))
 			continue;

 		GEM_BUG_ON(node_to_request(node)->engine->sched_engine !=
 			   sched_engine);

 		/* Must be called before changing the nodes priority */
 		if (sched_engine->bump_inflight_request_prio)
 			sched_engine->bump_inflight_request_prio(from, prio);

 		WRITE_ONCE(node->attr.priority, prio);

 		/*
 		 * Once the request is ready, it will be placed into the
 		 * priority lists and then onto the HW runlist. Before the
 		 * request is ready, it does not contribute to our preemption
 		 * decisions and we can safely ignore it, as it will, and
 		 * any preemption required, be dealt with upon submission.
 		 * See engine->submit_request()
 		 */
 		if (list_empty(&node->link))
 			continue;

 		if (i915_request_in_priority_queue(node_to_request(node))) {
 			if (!cache.priolist)
 				cache.priolist =
 					i915_sched_lookup_priolist(sched_engine,
 								   prio);
 			list_move_tail(&node->link, cache.priolist);
 		}

 		/* Defer (tasklet) submission until after all of our updates. */
 		if (sched_engine->kick_backend)
 			sched_engine->kick_backend(node_to_request(node), prio);
 	}

 	spin_unlock(&sched_engine->lock);
 }

 void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
 {
 	spin_lock_irq(&schedule_lock);
 	__i915_schedule(&rq->sched, attr);
 	spin_unlock_irq(&schedule_lock);
 }

 void i915_sched_node_init(struct i915_sched_node *node)
 {
 	INIT_LIST_HEAD(&node->signalers_list);
 	INIT_LIST_HEAD(&node->waiters_list);
 	INIT_LIST_HEAD(&node->link);

 	i915_sched_node_reinit(node);
 }

 void i915_sched_node_reinit(struct i915_sched_node *node)
 {
 	node->attr.priority = I915_PRIORITY_INVALID;
 	node->semaphores = 0;
 	node->flags = 0;

 	GEM_BUG_ON(!list_empty(&node->signalers_list));
 	GEM_BUG_ON(!list_empty(&node->waiters_list));
 	GEM_BUG_ON(!list_empty(&node->link));
 }

 static struct i915_dependency *
 i915_dependency_alloc(void)
 {
 	return kmem_cache_alloc(slab_dependencies, GFP_KERNEL);
 }

 static void
 i915_dependency_free(struct i915_dependency *dep)
 {
 	kmem_cache_free(slab_dependencies, dep);
 }

 bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
 				      struct i915_sched_node *signal,
 				      struct i915_dependency *dep,
 				      unsigned long flags)
 {
 	bool ret = false;

 	spin_lock_irq(&schedule_lock);

 	if (!node_signaled(signal)) {
 		INIT_LIST_HEAD(&dep->dfs_link);
 		dep->signaler = signal;
 		dep->waiter = node;
 		dep->flags = flags;

 		/* All set, now publish. Beware the lockless walkers. */
 		list_add_rcu(&dep->signal_link, &node->signalers_list);
 		list_add_rcu(&dep->wait_link, &signal->waiters_list);

 		/* Propagate the chains */
 		node->flags |= signal->flags;
 		ret = true;
 	}

 	spin_unlock_irq(&schedule_lock);

 	return ret;
 }

 int i915_sched_node_add_dependency(struct i915_sched_node *node,
 				   struct i915_sched_node *signal,
 				   unsigned long flags)
 {
 	struct i915_dependency *dep;

 	dep = i915_dependency_alloc();
 	if (!dep)
 		return -ENOMEM;

 	if (!__i915_sched_node_add_dependency(node, signal, dep,
 					      flags | I915_DEPENDENCY_ALLOC))
 		i915_dependency_free(dep);

 	return 0;
 }

 void i915_sched_node_fini(struct i915_sched_node *node)
 {
 	struct i915_dependency *dep, *tmp;

 	spin_lock_irq(&schedule_lock);

 	/*
 	 * Everyone we depended upon (the fences we wait to be signaled)
 	 * should retire before us and remove themselves from our list.
 	 * However, retirement is run independently on each timeline and
 	 * so we may be called out-of-order.
 	 */
 	list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
 		GEM_BUG_ON(!list_empty(&dep->dfs_link));

 		list_del_rcu(&dep->wait_link);
 		if (dep->flags & I915_DEPENDENCY_ALLOC)
 			i915_dependency_free(dep);
 	}
 	INIT_LIST_HEAD(&node->signalers_list);

 	/* Remove ourselves from everyone who depends upon us */
 	list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
 		GEM_BUG_ON(dep->signaler != node);
 		GEM_BUG_ON(!list_empty(&dep->dfs_link));

 		list_del_rcu(&dep->signal_link);
 		if (dep->flags & I915_DEPENDENCY_ALLOC)
 			i915_dependency_free(dep);
 	}
 	INIT_LIST_HEAD(&node->waiters_list);

 	spin_unlock_irq(&schedule_lock);
 }

 void i915_request_show_with_schedule(struct drm_printer *m,
 				     const struct i915_request *rq,
 				     const char *prefix,
 				     int indent)
 {
 	struct i915_dependency *dep;

 	i915_request_show(m, rq, prefix, indent);
 	if (i915_request_completed(rq))
 		return;

 	rcu_read_lock();
 	for_each_signaler(dep, rq) {
 		const struct i915_request *signaler =
 			node_to_request(dep->signaler);

 		/* Dependencies along the same timeline are expected. */
 		if (signaler->timeline == rq->timeline)
 			continue;

 		if (__i915_request_is_complete(signaler))
 			continue;

 		i915_request_show(m, signaler, prefix, indent + 2);
 	}
 	rcu_read_unlock();
 }

 static void default_destroy(struct kref *kref)
 {
 	struct i915_sched_engine *sched_engine =
 		container_of(kref, typeof(*sched_engine), ref);

 	tasklet_kill(&sched_engine->tasklet); /* flush the callback */
 	kfree(sched_engine);
 }

 static bool default_disabled(struct i915_sched_engine *sched_engine)
 {
 	return false;
 }

 struct i915_sched_engine *
 i915_sched_engine_create(unsigned int subclass)
 {
 	struct i915_sched_engine *sched_engine;

 	sched_engine = kzalloc(sizeof(*sched_engine), GFP_KERNEL);
 	if (!sched_engine)
 		return NULL;

 	kref_init(&sched_engine->ref);

 	sched_engine->queue = RB_ROOT_CACHED;
 	sched_engine->queue_priority_hint = INT_MIN;
 	sched_engine->destroy = default_destroy;
 	sched_engine->disabled = default_disabled;

 	INIT_LIST_HEAD(&sched_engine->requests);
 	INIT_LIST_HEAD(&sched_engine->hold);

 	spin_lock_init(&sched_engine->lock);
 	lockdep_set_subclass(&sched_engine->lock, subclass);

 	/*
 	 * Due to an interesting quirk in lockdep's internal debug tracking,
 	 * after setting a subclass we must ensure the lock is used. Otherwise,
 	 * nr_unused_locks is incremented once too often.
 	 */
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	local_irq_disable();
 	lock_map_acquire(&sched_engine->lock.dep_map);
 	lock_map_release(&sched_engine->lock.dep_map);
 	local_irq_enable();
 #endif

 	return sched_engine;
 }

 void i915_scheduler_module_exit(void)
 {
 	kmem_cache_destroy(slab_dependencies);
 	kmem_cache_destroy(slab_priorities);
 }

 int __init i915_scheduler_module_init(void)
 {
 	slab_dependencies = KMEM_CACHE(i915_dependency,
 					      SLAB_HWCACHE_ALIGN |
 					      SLAB_TYPESAFE_BY_RCU);
 	if (!slab_dependencies)
 		return -ENOMEM;

 	slab_priorities = KMEM_CACHE(i915_priolist, 0);
 	if (!slab_priorities)
 		goto err_priorities;

 	return 0;

 err_priorities:
 	kmem_cache_destroy(slab_priorities);
 	return -ENOMEM;
 }
	/*
	* SPDX-License-Identifier: MIT
	*
	* Copyright © 2018 Intel Corporation
	*/

	#include <linux/mutex.h>

	#include "i915_drv.h"
	#include "i915_request.h"
	#include "i915_scheduler.h"

	static struct kmem_cache *slab_dependencies;
	static struct kmem_cache *slab_priorities;

	static DEFINE_SPINLOCK(schedule_lock);

	static const struct i915_request *
	node_to_request(const struct i915_sched_node *node)
	{
	return container_of(node, const struct i915_request, sched);
	}

	static inline bool node_started(const struct i915_sched_node *node)
	{
	return i915_request_started(node_to_request(node));
	}

	static inline bool node_signaled(const struct i915_sched_node *node)
	{
	return i915_request_completed(node_to_request(node));
	}

	static inline struct i915_priolist to_priolist(struct rb_node rb)
	{
	return rb_entry(rb, struct i915_priolist, node);
	}

	static void assert_priolists(struct i915_sched_engine * const sched_engine)
	{
	struct rb_node *rb;
	long last_prio;

	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
	return;

	GEM_BUG_ON(rb_first_cached(&sched_engine->queue) !=
	rb_first(&sched_engine->queue.rb_root));

	last_prio = INT_MAX;
	for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
	const struct i915_priolist *p = to_priolist(rb);

	GEM_BUG_ON(p->priority > last_prio);
	last_prio = p->priority;
	}
	}

	struct list_head *
	i915_sched_lookup_priolist(struct i915_sched_engine *sched_engine, int prio)
	{
	struct i915_priolist *p;
	struct rb_node *parent, rb;
	bool first = true;

	lockdep_assert_held(&sched_engine->lock);
	assert_priolists(sched_engine);

	if (unlikely(sched_engine->no_priolist))
	prio = I915_PRIORITY_NORMAL;

	find_priolist:
	/* most positive priority is scheduled first, equal priorities fifo */
	rb = NULL;
	parent = &sched_engine->queue.rb_root.rb_node;
	while (*parent) {
	rb = *parent;
	p = to_priolist(rb);
	if (prio > p->priority) {
	parent = &rb->rb_left;
	} else if (prio < p->priority) {
	parent = &rb->rb_right;
	first = false;
	} else {
	return &p->requests;
	}
	}

	if (prio == I915_PRIORITY_NORMAL) {
	p = &sched_engine->default_priolist;
	} else {
	p = kmem_cache_alloc(slab_priorities, GFP_ATOMIC);
	/* Convert an allocation failure to a priority bump */
	if (unlikely(!p)) {
	prio = I915_PRIORITY_NORMAL; /* recurses just once */

	/* To maintain ordering with all rendering, after an
	* allocation failure we have to disable all scheduling.
	* Requests will then be executed in fifo, and schedule
	* will ensure that dependencies are emitted in fifo.
	* There will be still some reordering with existing
	* requests, so if userspace lied about their
	* dependencies that reordering may be visible.
	*/
	sched_engine->no_priolist = true;
	goto find_priolist;
	}
	}

	p->priority = prio;
	INIT_LIST_HEAD(&p->requests);

	rb_link_node(&p->node, rb, parent);
	rb_insert_color_cached(&p->node, &sched_engine->queue, first);

	return &p->requests;
	}

	void __i915_priolist_free(struct i915_priolist *p)
	{
	kmem_cache_free(slab_priorities, p);
	}

	struct sched_cache {
	struct list_head *priolist;
	};

	static struct i915_sched_engine *
	lock_sched_engine(struct i915_sched_node *node,
	struct i915_sched_engine *locked,
	struct sched_cache *cache)
	{
	const struct i915_request *rq = node_to_request(node);
	struct i915_sched_engine *sched_engine;

	GEM_BUG_ON(!locked);

	/*
	* Virtual engines complicate acquiring the engine timeline lock,
	* as their rq->engine pointer is not stable until under that
	* engine lock. The simple ploy we use is to take the lock then
	* check that the rq still belongs to the newly locked engine.
	*/
	while (locked != (sched_engine = READ_ONCE(rq->engine)->sched_engine)) {
	spin_unlock(&locked->lock);
	memset(cache, 0, sizeof(*cache));
	spin_lock(&sched_engine->lock);
	locked = sched_engine;
	}

	GEM_BUG_ON(locked != sched_engine);
	return locked;
	}

	static void __i915_schedule(struct i915_sched_node *node,
	const struct i915_sched_attr *attr)
	{
	const int prio = max(attr->priority, node->attr.priority);
	struct i915_sched_engine *sched_engine;
	struct i915_dependency dep, p;
	struct i915_dependency stack;
	struct sched_cache cache;
	LIST_HEAD(dfs);

	/* Needed in order to use the temporary link inside i915_dependency */
	lockdep_assert_held(&schedule_lock);
	GEM_BUG_ON(prio == I915_PRIORITY_INVALID);

	if (node_signaled(node))
	return;

	stack.signaler = node;
	list_add(&stack.dfs_link, &dfs);

	/*
	* Recursively bump all dependent priorities to match the new request.
	*
	* A naive approach would be to use recursion:
	* static void update_priorities(struct i915_sched_node *node, prio) {
	* list_for_each_entry(dep, &node->signalers_list, signal_link)
	* update_priorities(dep->signal, prio)
	* queue_request(node);
	* }
	* but that may have unlimited recursion depth and so runs a very
	* real risk of overunning the kernel stack. Instead, we build
	* a flat list of all dependencies starting with the current request.
	* As we walk the list of dependencies, we add all of its dependencies
	* to the end of the list (this may include an already visited
	* request) and continue to walk onwards onto the new dependencies. The
	* end result is a topological list of requests in reverse order, the
	* last element in the list is the request we must execute first.
	*/
	list_for_each_entry(dep, &dfs, dfs_link) {
	struct i915_sched_node *node = dep->signaler;

	/* If we are already flying, we know we have no signalers */
	if (node_started(node))
	continue;

	/*
	* Within an engine, there can be no cycle, but we may
	* refer to the same dependency chain multiple times
	* (redundant dependencies are not eliminated) and across
	* engines.
	*/
	list_for_each_entry(p, &node->signalers_list, signal_link) {
	GEM_BUG_ON(p == dep); /* no cycles! */

	if (node_signaled(p->signaler))
	continue;

	if (prio > READ_ONCE(p->signaler->attr.priority))
	list_move_tail(&p->dfs_link, &dfs);
	}
	}

	/*
	* If we didn't need to bump any existing priorities, and we haven't
	* yet submitted this request (i.e. there is no potential race with
	* execlists_submit_request()), we can set our own priority and skip
	* acquiring the engine locks.
	*/
	if (node->attr.priority == I915_PRIORITY_INVALID) {
	GEM_BUG_ON(!list_empty(&node->link));
	node->attr = *attr;

	if (stack.dfs_link.next == stack.dfs_link.prev)
	return;

	__list_del_entry(&stack.dfs_link);
	}

	memset(&cache, 0, sizeof(cache));
	sched_engine = node_to_request(node)->engine->sched_engine;
	spin_lock(&sched_engine->lock);

	/* Fifo and depth-first replacement ensure our deps execute before us */
	sched_engine = lock_sched_engine(node, sched_engine, &cache);
	list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
	struct i915_request *from = container_of(dep->signaler,
	struct i915_request,
	sched);
	INIT_LIST_HEAD(&dep->dfs_link);

	node = dep->signaler;
	sched_engine = lock_sched_engine(node, sched_engine, &cache);
	lockdep_assert_held(&sched_engine->lock);

	/* Recheck after acquiring the engine->timeline.lock */
	if (prio <= node->attr.priority \|\| node_signaled(node))
	continue;

	GEM_BUG_ON(node_to_request(node)->engine->sched_engine !=
	sched_engine);

	/* Must be called before changing the nodes priority */
	if (sched_engine->bump_inflight_request_prio)
	sched_engine->bump_inflight_request_prio(from, prio);

	WRITE_ONCE(node->attr.priority, prio);

	/*
	* Once the request is ready, it will be placed into the
	* priority lists and then onto the HW runlist. Before the
	* request is ready, it does not contribute to our preemption
	* decisions and we can safely ignore it, as it will, and
	* any preemption required, be dealt with upon submission.
	* See engine->submit_request()
	*/
	if (list_empty(&node->link))
	continue;

	if (i915_request_in_priority_queue(node_to_request(node))) {
	if (!cache.priolist)
	cache.priolist =
	i915_sched_lookup_priolist(sched_engine,
	prio);
	list_move_tail(&node->link, cache.priolist);
	}

	/* Defer (tasklet) submission until after all of our updates. */
	if (sched_engine->kick_backend)
	sched_engine->kick_backend(node_to_request(node), prio);
	}

	spin_unlock(&sched_engine->lock);
	}

	void i915_schedule(struct i915_request rq, const struct i915_sched_attr attr)
	{
	spin_lock_irq(&schedule_lock);
	__i915_schedule(&rq->sched, attr);
	spin_unlock_irq(&schedule_lock);
	}

	void i915_sched_node_init(struct i915_sched_node *node)
	{
	INIT_LIST_HEAD(&node->signalers_list);
	INIT_LIST_HEAD(&node->waiters_list);
	INIT_LIST_HEAD(&node->link);

	i915_sched_node_reinit(node);
	}

	void i915_sched_node_reinit(struct i915_sched_node *node)
	{
	node->attr.priority = I915_PRIORITY_INVALID;
	node->semaphores = 0;
	node->flags = 0;

	GEM_BUG_ON(!list_empty(&node->signalers_list));
	GEM_BUG_ON(!list_empty(&node->waiters_list));
	GEM_BUG_ON(!list_empty(&node->link));
	}

	static struct i915_dependency *
	i915_dependency_alloc(void)
	{
	return kmem_cache_alloc(slab_dependencies, GFP_KERNEL);
	}

	static void
	i915_dependency_free(struct i915_dependency *dep)
	{
	kmem_cache_free(slab_dependencies, dep);
	}

	bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
	struct i915_sched_node *signal,
	struct i915_dependency *dep,
	unsigned long flags)
	{
	bool ret = false;

	spin_lock_irq(&schedule_lock);

	if (!node_signaled(signal)) {
	INIT_LIST_HEAD(&dep->dfs_link);
	dep->signaler = signal;
	dep->waiter = node;
	dep->flags = flags;

	/* All set, now publish. Beware the lockless walkers. */
	list_add_rcu(&dep->signal_link, &node->signalers_list);
	list_add_rcu(&dep->wait_link, &signal->waiters_list);

	/* Propagate the chains */
	node->flags \|= signal->flags;
	ret = true;
	}

	spin_unlock_irq(&schedule_lock);

	return ret;
	}

	int i915_sched_node_add_dependency(struct i915_sched_node *node,
	struct i915_sched_node *signal,
	unsigned long flags)
	{
	struct i915_dependency *dep;

	dep = i915_dependency_alloc();
	if (!dep)
	return -ENOMEM;

	if (!__i915_sched_node_add_dependency(node, signal, dep,
	flags \| I915_DEPENDENCY_ALLOC))
	i915_dependency_free(dep);

	return 0;
	}

	void i915_sched_node_fini(struct i915_sched_node *node)
	{
	struct i915_dependency dep, tmp;

	spin_lock_irq(&schedule_lock);

	/*
	* Everyone we depended upon (the fences we wait to be signaled)
	* should retire before us and remove themselves from our list.
	* However, retirement is run independently on each timeline and
	* so we may be called out-of-order.
	*/
	list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
	GEM_BUG_ON(!list_empty(&dep->dfs_link));

	list_del_rcu(&dep->wait_link);
	if (dep->flags & I915_DEPENDENCY_ALLOC)
	i915_dependency_free(dep);
	}
	INIT_LIST_HEAD(&node->signalers_list);

	/* Remove ourselves from everyone who depends upon us */
	list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
	GEM_BUG_ON(dep->signaler != node);
	GEM_BUG_ON(!list_empty(&dep->dfs_link));

	list_del_rcu(&dep->signal_link);
	if (dep->flags & I915_DEPENDENCY_ALLOC)
	i915_dependency_free(dep);
	}
	INIT_LIST_HEAD(&node->waiters_list);

	spin_unlock_irq(&schedule_lock);
	}

	void i915_request_show_with_schedule(struct drm_printer *m,
	const struct i915_request *rq,
	const char *prefix,
	int indent)
	{
	struct i915_dependency *dep;

	i915_request_show(m, rq, prefix, indent);
	if (i915_request_completed(rq))
	return;

	rcu_read_lock();
	for_each_signaler(dep, rq) {
	const struct i915_request *signaler =
	node_to_request(dep->signaler);

	/* Dependencies along the same timeline are expected. */
	if (signaler->timeline == rq->timeline)
	continue;

	if (__i915_request_is_complete(signaler))
	continue;

	i915_request_show(m, signaler, prefix, indent + 2);
	}
	rcu_read_unlock();
	}

	static void default_destroy(struct kref *kref)
	{
	struct i915_sched_engine *sched_engine =
	container_of(kref, typeof(*sched_engine), ref);

	tasklet_kill(&sched_engine->tasklet); /* flush the callback */
	kfree(sched_engine);
	}

	static bool default_disabled(struct i915_sched_engine *sched_engine)
	{
	return false;
	}

	struct i915_sched_engine *
	i915_sched_engine_create(unsigned int subclass)
	{
	struct i915_sched_engine *sched_engine;

	sched_engine = kzalloc(sizeof(*sched_engine), GFP_KERNEL);
	if (!sched_engine)
	return NULL;

	kref_init(&sched_engine->ref);

	sched_engine->queue = RB_ROOT_CACHED;
	sched_engine->queue_priority_hint = INT_MIN;
	sched_engine->destroy = default_destroy;
	sched_engine->disabled = default_disabled;

	INIT_LIST_HEAD(&sched_engine->requests);
	INIT_LIST_HEAD(&sched_engine->hold);

	spin_lock_init(&sched_engine->lock);
	lockdep_set_subclass(&sched_engine->lock, subclass);

	/*
	* Due to an interesting quirk in lockdep's internal debug tracking,
	* after setting a subclass we must ensure the lock is used. Otherwise,
	* nr_unused_locks is incremented once too often.
	*/
	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	local_irq_disable();
	lock_map_acquire(&sched_engine->lock.dep_map);
	lock_map_release(&sched_engine->lock.dep_map);
	local_irq_enable();
	#endif

	return sched_engine;
	}

	void i915_scheduler_module_exit(void)
	{
	kmem_cache_destroy(slab_dependencies);
	kmem_cache_destroy(slab_priorities);
	}

	int __init i915_scheduler_module_init(void)
	{
	slab_dependencies = KMEM_CACHE(i915_dependency,
	SLAB_HWCACHE_ALIGN \|
	SLAB_TYPESAFE_BY_RCU);
	if (!slab_dependencies)
	return -ENOMEM;

	slab_priorities = KMEM_CACHE(i915_priolist, 0);
	if (!slab_priorities)
	goto err_priorities;

	return 0;

	err_priorities:
	kmem_cache_destroy(slab_priorities);
	return -ENOMEM;
	}