drivers/gpu/drm/i915/i915_scheduler.c - SHIFTPHONES/mainline/linux - Gitiles

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

 #include <linux/mutex.h>

 #include "i915_drv.h"
 #include "i915_globals.h"
 #include "i915_request.h"
 #include "i915_scheduler.h"

 static struct i915_global_scheduler {
 	struct i915_global base;
 	struct kmem_cache *slab_dependencies;
 	struct kmem_cache *slab_priorities;
 } global;

 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 intel_engine_execlists * const execlists)
 {
 	struct rb_node *rb;
 	long last_prio, i;

 	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
 		return;

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

 	last_prio = (INT_MAX >> I915_USER_PRIORITY_SHIFT) + 1;
 	for (rb = rb_first_cached(&execlists->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;

 		GEM_BUG_ON(!p->used);
 		for (i = 0; i < ARRAY_SIZE(p->requests); i++) {
 			if (list_empty(&p->requests[i]))
 				continue;

 			GEM_BUG_ON(!(p->used & BIT(i)));
 		}
 	}
 }

 struct list_head *
 i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
 	struct i915_priolist *p;
 	struct rb_node **parent, *rb;
 	bool first = true;
 	int idx, i;

 	lockdep_assert_held(&engine->active.lock);
 	assert_priolists(execlists);

 	/* buckets sorted from highest [in slot 0] to lowest priority */
 	idx = I915_PRIORITY_COUNT - (prio & I915_PRIORITY_MASK) - 1;
 	prio >>= I915_USER_PRIORITY_SHIFT;
 	if (unlikely(execlists->no_priolist))
 		prio = I915_PRIORITY_NORMAL;

 find_priolist:
 	/* most positive priority is scheduled first, equal priorities fifo */
 	rb = NULL;
 	parent = &execlists->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 {
 			goto out;
 		}
 	}

 	if (prio == I915_PRIORITY_NORMAL) {
 		p = &execlists->default_priolist;
 	} else {
 		p = kmem_cache_alloc(global.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.
 			 */
 			execlists->no_priolist = true;
 			goto find_priolist;
 		}
 	}

 	p->priority = prio;
 	for (i = 0; i < ARRAY_SIZE(p->requests); i++)
 		INIT_LIST_HEAD(&p->requests[i]);
 	rb_link_node(&p->node, rb, parent);
 	rb_insert_color_cached(&p->node, &execlists->queue, first);
 	p->used = 0;

 out:
 	p->used |= BIT(idx);
 	return &p->requests[idx];
 }

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

 struct sched_cache {
 	struct list_head *priolist;
 };

 static struct intel_engine_cs *
 sched_lock_engine(const struct i915_sched_node *node,
 		  struct intel_engine_cs *locked,
 		  struct sched_cache *cache)
 {
 	const struct i915_request *rq = node_to_request(node);
 	struct intel_engine_cs *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 != (engine = READ_ONCE(rq->engine))) {
 		spin_unlock(&locked->active.lock);
 		memset(cache, 0, sizeof(*cache));
 		spin_lock(&engine->active.lock);
 		locked = engine;
 	}

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

 static inline int rq_prio(const struct i915_request *rq)
 {
 	return rq->sched.attr.priority | __NO_PREEMPTION;
 }

 static inline bool need_preempt(int prio, int active)
 {
 	/*
 	 * Allow preemption of low -> normal -> high, but we do
 	 * not allow low priority tasks to preempt other low priority
 	 * tasks under the impression that latency for low priority
 	 * tasks does not matter (as much as background throughput),
 	 * so kiss.
 	 */
 	return prio >= max(I915_PRIORITY_NORMAL, active);
 }

 static void kick_submission(struct intel_engine_cs *engine,
 			    const struct i915_request *rq,
 			    int prio)
 {
 	const struct i915_request *inflight;

 	/*
 	 * We only need to kick the tasklet once for the high priority
 	 * new context we add into the queue.
 	 */
 	if (prio <= engine->execlists.queue_priority_hint)
 		return;

 	rcu_read_lock();

 	/* Nothing currently active? We're overdue for a submission! */
 	inflight = execlists_active(&engine->execlists);
 	if (!inflight)
 		goto unlock;

 	/*
 	 * If we are already the currently executing context, don't
 	 * bother evaluating if we should preempt ourselves.
 	 */
 	if (inflight->context == rq->context)
 		goto unlock;

 	engine->execlists.queue_priority_hint = prio;
 	if (need_preempt(prio, rq_prio(inflight)))
 		tasklet_hi_schedule(&engine->execlists.tasklet);

 unlock:
 	rcu_read_unlock();
 }

 static void __i915_schedule(struct i915_sched_node *node,
 			    const struct i915_sched_attr *attr)
 {
 	struct intel_engine_cs *engine;
 	struct i915_dependency *dep, *p;
 	struct i915_dependency stack;
 	const int prio = attr->priority;
 	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 (prio <= READ_ONCE(node->attr.priority))
 		return;

 	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));
 	engine = node_to_request(node)->engine;
 	spin_lock(&engine->active.lock);

 	/* Fifo and depth-first replacement ensure our deps execute before us */
 	engine = sched_lock_engine(node, engine, &cache);
 	list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
 		INIT_LIST_HEAD(&dep->dfs_link);

 		node = dep->signaler;
 		engine = sched_lock_engine(node, engine, &cache);
 		lockdep_assert_held(&engine->active.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 != engine);

 		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(engine,
 								   prio);
 			list_move_tail(&node->link, cache.priolist);
 		}

 		/* Defer (tasklet) submission until after all of our updates. */
 		kick_submission(engine, node_to_request(node), prio);
 	}

 	spin_unlock(&engine->active.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);
 }

 static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
 {
 	struct i915_sched_attr attr = node->attr;

 	attr.priority |= bump;
 	__i915_schedule(node, &attr);
 }

 void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
 {
 	unsigned long flags;

 	GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
 	if (READ_ONCE(rq->sched.attr.priority) & bump)
 		return;

 	spin_lock_irqsave(&schedule_lock, flags);
 	__bump_priority(&rq->sched, bump);
 	spin_unlock_irqrestore(&schedule_lock, flags);
 }

 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(global.slab_dependencies, GFP_KERNEL);
 }

 static void
 i915_dependency_free(struct i915_dependency *dep)
 {
 	kmem_cache_free(global.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;

 		/* Keep track of whether anyone on this chain has a semaphore */
 		if (signal->flags & I915_SCHED_HAS_SEMAPHORE_CHAIN &&
 		    !node_started(signal))
 			node->flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;

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

 		/*
 		 * As we do not allow WAIT to preempt inflight requests,
 		 * once we have executed a request, along with triggering
 		 * any execution callbacks, we must preserve its ordering
 		 * within the non-preemptible FIFO.
 		 */
 		BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
 		if (flags & I915_DEPENDENCY_EXTERNAL)
 			__bump_priority(signal, __NO_PREEMPTION);

 		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)
 {
 	struct i915_dependency *dep;

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

 	if (!__i915_sched_node_add_dependency(node, signal, dep,
 					      I915_DEPENDENCY_EXTERNAL |
 					      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(&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(&dep->signal_link);
 		if (dep->flags & I915_DEPENDENCY_ALLOC)
 			i915_dependency_free(dep);
 	}
 	INIT_LIST_HEAD(&node->waiters_list);

 	spin_unlock_irq(&schedule_lock);
 }

 static void i915_global_scheduler_shrink(void)
 {
 	kmem_cache_shrink(global.slab_dependencies);
 	kmem_cache_shrink(global.slab_priorities);
 }

 static void i915_global_scheduler_exit(void)
 {
 	kmem_cache_destroy(global.slab_dependencies);
 	kmem_cache_destroy(global.slab_priorities);
 }

 static struct i915_global_scheduler global = { {
 	.shrink = i915_global_scheduler_shrink,
 	.exit = i915_global_scheduler_exit,
 } };

 int __init i915_global_scheduler_init(void)
 {
 	global.slab_dependencies = KMEM_CACHE(i915_dependency,
 					      SLAB_HWCACHE_ALIGN);
 	if (!global.slab_dependencies)
 		return -ENOMEM;

 	global.slab_priorities = KMEM_CACHE(i915_priolist,
 					    SLAB_HWCACHE_ALIGN);
 	if (!global.slab_priorities)
 		goto err_priorities;

 	i915_global_register(&global.base);
 	return 0;

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

	#include <linux/mutex.h>

	#include "i915_drv.h"
	#include "i915_globals.h"
	#include "i915_request.h"
	#include "i915_scheduler.h"

	static struct i915_global_scheduler {
	struct i915_global base;
	struct kmem_cache *slab_dependencies;
	struct kmem_cache *slab_priorities;
	} global;

	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 intel_engine_execlists * const execlists)
	{
	struct rb_node *rb;
	long last_prio, i;

	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
	return;

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

	last_prio = (INT_MAX >> I915_USER_PRIORITY_SHIFT) + 1;
	for (rb = rb_first_cached(&execlists->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;

	GEM_BUG_ON(!p->used);
	for (i = 0; i < ARRAY_SIZE(p->requests); i++) {
	if (list_empty(&p->requests[i]))
	continue;

	GEM_BUG_ON(!(p->used & BIT(i)));
	}
	}
	}

	struct list_head *
	i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
	{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	struct i915_priolist *p;
	struct rb_node *parent, rb;
	bool first = true;
	int idx, i;

	lockdep_assert_held(&engine->active.lock);
	assert_priolists(execlists);

	/* buckets sorted from highest [in slot 0] to lowest priority */
	idx = I915_PRIORITY_COUNT - (prio & I915_PRIORITY_MASK) - 1;
	prio >>= I915_USER_PRIORITY_SHIFT;
	if (unlikely(execlists->no_priolist))
	prio = I915_PRIORITY_NORMAL;

	find_priolist:
	/* most positive priority is scheduled first, equal priorities fifo */
	rb = NULL;
	parent = &execlists->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 {
	goto out;
	}
	}

	if (prio == I915_PRIORITY_NORMAL) {
	p = &execlists->default_priolist;
	} else {
	p = kmem_cache_alloc(global.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.
	*/
	execlists->no_priolist = true;
	goto find_priolist;
	}
	}

	p->priority = prio;
	for (i = 0; i < ARRAY_SIZE(p->requests); i++)
	INIT_LIST_HEAD(&p->requests[i]);
	rb_link_node(&p->node, rb, parent);
	rb_insert_color_cached(&p->node, &execlists->queue, first);
	p->used = 0;

	out:
	p->used \|= BIT(idx);
	return &p->requests[idx];
	}

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

	struct sched_cache {
	struct list_head *priolist;
	};

	static struct intel_engine_cs *
	sched_lock_engine(const struct i915_sched_node *node,
	struct intel_engine_cs *locked,
	struct sched_cache *cache)
	{
	const struct i915_request *rq = node_to_request(node);
	struct intel_engine_cs *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 != (engine = READ_ONCE(rq->engine))) {
	spin_unlock(&locked->active.lock);
	memset(cache, 0, sizeof(*cache));
	spin_lock(&engine->active.lock);
	locked = engine;
	}

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

	static inline int rq_prio(const struct i915_request *rq)
	{
	return rq->sched.attr.priority \| __NO_PREEMPTION;
	}

	static inline bool need_preempt(int prio, int active)
	{
	/*
	* Allow preemption of low -> normal -> high, but we do
	* not allow low priority tasks to preempt other low priority
	* tasks under the impression that latency for low priority
	* tasks does not matter (as much as background throughput),
	* so kiss.
	*/
	return prio >= max(I915_PRIORITY_NORMAL, active);
	}

	static void kick_submission(struct intel_engine_cs *engine,
	const struct i915_request *rq,
	int prio)
	{
	const struct i915_request *inflight;

	/*
	* We only need to kick the tasklet once for the high priority
	* new context we add into the queue.
	*/
	if (prio <= engine->execlists.queue_priority_hint)
	return;

	rcu_read_lock();

	/* Nothing currently active? We're overdue for a submission! */
	inflight = execlists_active(&engine->execlists);
	if (!inflight)
	goto unlock;

	/*
	* If we are already the currently executing context, don't
	* bother evaluating if we should preempt ourselves.
	*/
	if (inflight->context == rq->context)
	goto unlock;

	engine->execlists.queue_priority_hint = prio;
	if (need_preempt(prio, rq_prio(inflight)))
	tasklet_hi_schedule(&engine->execlists.tasklet);

	unlock:
	rcu_read_unlock();
	}

	static void __i915_schedule(struct i915_sched_node *node,
	const struct i915_sched_attr *attr)
	{
	struct intel_engine_cs *engine;
	struct i915_dependency dep, p;
	struct i915_dependency stack;
	const int prio = attr->priority;
	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 (prio <= READ_ONCE(node->attr.priority))
	return;

	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));
	engine = node_to_request(node)->engine;
	spin_lock(&engine->active.lock);

	/* Fifo and depth-first replacement ensure our deps execute before us */
	engine = sched_lock_engine(node, engine, &cache);
	list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
	INIT_LIST_HEAD(&dep->dfs_link);

	node = dep->signaler;
	engine = sched_lock_engine(node, engine, &cache);
	lockdep_assert_held(&engine->active.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 != engine);

	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(engine,
	prio);
	list_move_tail(&node->link, cache.priolist);
	}

	/* Defer (tasklet) submission until after all of our updates. */
	kick_submission(engine, node_to_request(node), prio);
	}

	spin_unlock(&engine->active.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);
	}

	static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
	{
	struct i915_sched_attr attr = node->attr;

	attr.priority \|= bump;
	__i915_schedule(node, &attr);
	}

	void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
	{
	unsigned long flags;

	GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
	if (READ_ONCE(rq->sched.attr.priority) & bump)
	return;

	spin_lock_irqsave(&schedule_lock, flags);
	__bump_priority(&rq->sched, bump);
	spin_unlock_irqrestore(&schedule_lock, flags);
	}

	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(global.slab_dependencies, GFP_KERNEL);
	}

	static void
	i915_dependency_free(struct i915_dependency *dep)
	{
	kmem_cache_free(global.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;

	/* Keep track of whether anyone on this chain has a semaphore */
	if (signal->flags & I915_SCHED_HAS_SEMAPHORE_CHAIN &&
	!node_started(signal))
	node->flags \|= I915_SCHED_HAS_SEMAPHORE_CHAIN;

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

	/*
	* As we do not allow WAIT to preempt inflight requests,
	* once we have executed a request, along with triggering
	* any execution callbacks, we must preserve its ordering
	* within the non-preemptible FIFO.
	*/
	BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
	if (flags & I915_DEPENDENCY_EXTERNAL)
	__bump_priority(signal, __NO_PREEMPTION);

	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)
	{
	struct i915_dependency *dep;

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

	if (!__i915_sched_node_add_dependency(node, signal, dep,
	I915_DEPENDENCY_EXTERNAL \|
	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(&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(&dep->signal_link);
	if (dep->flags & I915_DEPENDENCY_ALLOC)
	i915_dependency_free(dep);
	}
	INIT_LIST_HEAD(&node->waiters_list);

	spin_unlock_irq(&schedule_lock);
	}

	static void i915_global_scheduler_shrink(void)
	{
	kmem_cache_shrink(global.slab_dependencies);
	kmem_cache_shrink(global.slab_priorities);
	}

	static void i915_global_scheduler_exit(void)
	{
	kmem_cache_destroy(global.slab_dependencies);
	kmem_cache_destroy(global.slab_priorities);
	}

	static struct i915_global_scheduler global = { {
	.shrink = i915_global_scheduler_shrink,
	.exit = i915_global_scheduler_exit,
	} };

	int __init i915_global_scheduler_init(void)
	{
	global.slab_dependencies = KMEM_CACHE(i915_dependency,
	SLAB_HWCACHE_ALIGN);
	if (!global.slab_dependencies)
	return -ENOMEM;

	global.slab_priorities = KMEM_CACHE(i915_priolist,
	SLAB_HWCACHE_ALIGN);
	if (!global.slab_priorities)
	goto err_priorities;

	i915_global_register(&global.base);
	return 0;

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