drm/i915: Start of GPU scheduler

Initial creation of scheduler source files. Note that this patch
implements most of the scheduler functionality but does not hook it in
to the driver yet. It also leaves the scheduler code in 'pass through'
mode so that even when it is hooked in, it will not actually do very
much. This allows the hooks to be added one at a time in bite size
chunks and only when the scheduler is finally enabled at the end does
anything start happening.

The general theory of operation is that when batch buffers are
submitted to the driver, the execbuffer() code packages up all the
information required to execute the batch buffer at a later time. This
package is given over to the scheduler which adds it to an internal
node list. The scheduler also scans the list of objects associated
with the batch buffer and compares them against the objects already in
use by other buffers in the node list. If matches are found then the
new batch buffer node is marked as being dependent upon the matching
node. The same is done for the context object. The scheduler also
bumps up the priority of such matching nodes on the grounds that the
more dependencies a given batch buffer has the more important it is
likely to be.

The scheduler aims to have a given (tuneable) number of batch buffers
in flight on the hardware at any given time. If fewer than this are
currently executing when a new node is queued, then the node is passed
straight through to the submit function. Otherwise it is simply added
to the queue and the driver returns back to user land.

The scheduler is notified when each batch buffer completes and updates
its internal tracking accordingly. At the end of the completion
interrupt processing, if any scheduler tracked batches were processed,
the scheduler's deferred worker thread is woken up. This can do more
involved processing such as actually removing completed nodes from the
queue and freeing up the resources associated with them (internal
memory allocations, DRM object references, context reference, etc.).
The work handler also checks the in flight count and calls the
submission code if a new slot has appeared.

When the scheduler's submit code is called, it scans the queued node
list for the highest priority node that has no unmet dependencies.
Note that the dependency calculation is complex as it must take
inter-ring dependencies and potential preemptions into account. Note
also that in the future this will be extended to include external
dependencies such as the Android Native Sync file descriptors and/or
the linux dma-buff synchronisation scheme.

If a suitable node is found then it is sent to execbuff_final() for
submission to the hardware. The in flight count is then re-checked and
a new node popped from the list if appropriate. All nodes that are not
submitted have their priority bumped. This ensures that low priority
tasks do not get starved out by busy higher priority ones - everything
will eventually get its turn to run.

Note that this patch does not implement pre-emptive scheduling. Only
basic scheduling by re-ordering batch buffer submission is currently
implemented. Pre-emption of actively executing batch buffers comes in
the next patch series.

v2: Changed priority levels to +/-1023 due to feedback from Chris
Wilson.

Removed redundant index from scheduler node.

Changed time stamps to use jiffies instead of raw monotonic. This
provides lower resolution but improved compatibility with other i915
code.

Major re-write of completion tracking code due to struct fence
conversion. The scheduler no longer has it's own private IRQ handler
but just lets the existing request code handle completion events.
Instead, the scheduler now hooks into the request notify code to be
told when a request has completed.

Reduced driver mutex locking scope. Removal of scheduler nodes no
longer grabs the mutex lock.

v3: Refactor of dependency generation to make the code more readable.
Also added in read-read optimisation support - i.e., don't treat a
shared read-only buffer as being a dependency.

Allowed the killing of queued nodes rather than only flying ones.

v4: Updated the commit message to better reflect the current state of
the code. Downgraded some BUG_ONs to WARN_ONs. Used the correct array
memory allocator function (kmalloc_array instead of kmalloc).
Corrected the format of some comments. Wrapped some lines differently
to keep the style checker happy.

Fixed a WARN_ON when killing nodes. The dependency removal code checks
that nodes being destroyed do not have any oustanding dependencies
(which would imply they should not have been executed yet). In the
case of nodes being destroyed, e.g. due to context banning, then this
might well be the case - they have not been executed and do indeed
have outstanding dependencies.

Re-instated the code to disble interrupts when not in use. The
underlying problem causing broken IRQ reference counts seems to have
been fixed now.

v5: Shuffled various functions around to remove forward declarations
as apparently these are frowned upon. Removed lots of white space as
apparently having easy to read code is also frowned upon. Split the
direct submission scheduler bypass code out into a separate function.
Squashed down the i915_scheduler.c sections of various patches into
this patch. Thus the later patches simply hook in existing code into
various parts of the driver rather than adding the code as well. Added
documentation to various functions. Re-worked the submit function in
terms of mutex locking, error handling and exit paths. Split the
delayed work handler function in half. Made use of the kernel 'clamp'
macro. [Joonas Lahtinen]

Added runtime PM calls as these must be done at the top level before
acquiring the driver mutex lock. [Chris Wilson]

Removed some obsolete debug code that had been forgotten about.

Moved more clean up code into the 'i915_gem_scheduler_clean_node()'
function rather than replicating it in mutliple places.

Used lighter weight spinlocks.

For: VIZ-1587
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

6 files changed, 991 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 95ad56b6aab3..d6d5afbcf8d1 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -10,6 +10,7 @@
 i915-y := i915_drv.o \
 	  i915_irq.o \
 	  i915_params.o \
+	  i915_scheduler.o \
           i915_suspend.o \
 	  i915_sysfs.o \
 	  intel_csr.o \
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index fc8ac98c12d7..63b32763b438 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -37,6 +37,7 @@
 #include "i915_drv.h"
 #include "i915_vgpu.h"
 #include "i915_trace.h"
+#include "i915_scheduler.h"
 #include <linux/pci.h>
 #include <linux/console.h>
 #include <linux/vt.h>
@@ -1445,6 +1446,8 @@ int i915_driver_unload(struct drm_device *dev)
 
 	intel_csr_ucode_fini(dev_priv);
 
+	i915_scheduler_destroy(dev_priv);
+
 	/* Free error state after interrupts are fully disabled. */
 	cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
 	i915_destroy_error_state(dev);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 8d7d796a73be..29dbed927a37 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1701,6 +1701,8 @@ struct i915_execbuffer_params {
 	struct drm_i915_gem_request     *request;
 };
 
+struct i915_scheduler;
+
 /* used in computing the new watermarks state */
 struct intel_wm_config {
 	unsigned int num_pipes_active;
@@ -1969,6 +1971,8 @@ struct drm_i915_private {
 
 	struct i915_runtime_pm pm;
 
+	struct i915_scheduler *scheduler;
+
 	/* Abstract the submission mechanism (legacy ringbuffer or execlists) away */
 	struct {
 		int (*execbuf_submit)(struct i915_execbuffer_params *params,
@@ -2301,6 +2305,8 @@ struct drm_i915_gem_request {
 	/** process identifier submitting this request */
 	struct pid *pid;
 
+	struct i915_scheduler_queue_entry *scheduler_qe;
+
 	/**
 	 * The ELSP only accepts two elements at a time, so we queue
 	 * context/tail pairs on a given queue (ring->execlist_queue) until the
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f8c69ec6de63..66d9c8d9a81c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -32,6 +32,7 @@
 #include "i915_vgpu.h"
 #include "i915_trace.h"
 #include "intel_drv.h"
+#include "i915_scheduler.h"
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
@@ -5334,6 +5335,10 @@ int i915_gem_init(struct drm_device *dev)
 	 */
 	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
 
+	ret = i915_scheduler_init(dev);
+	if (ret)
+		goto out_unlock;
+
 	ret = i915_gem_init_userptr(dev);
 	if (ret)
 		goto out_unlock;
diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
new file mode 100644
index 000000000000..af2bd1691378
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -0,0 +1,863 @@
+/*
+ * Copyright (c) 2014 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "i915_drv.h"
+#include "intel_drv.h"
+#include "i915_scheduler.h"
+
+#define for_each_scheduler_node(node, id)				\
+	list_for_each_entry((node), &scheduler->node_queue[(id)], link)
+
+#define assert_scheduler_lock_held(scheduler)				\
+	do {								\
+		WARN_ONCE(!spin_is_locked(&(scheduler)->lock), "Spinlock not locked!");	\
+	} while(0)
+
+/**
+ * i915_scheduler_is_enabled - Returns true if the scheduler is enabled.
+ * @dev: DRM device
+ */
+bool i915_scheduler_is_enabled(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = to_i915(dev);
+
+	return dev_priv->scheduler != NULL;
+}
+
+/**
+ * i915_scheduler_init - Initialise the scheduler.
+ * @dev: DRM device
+ * Returns zero on success or -ENOMEM if memory allocations fail.
+ */
+int i915_scheduler_init(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	int e;
+
+	if (scheduler)
+		return 0;
+
+	scheduler = kzalloc(sizeof(*scheduler), GFP_KERNEL);
+	if (!scheduler)
+		return -ENOMEM;
+
+	spin_lock_init(&scheduler->lock);
+
+	for (e = 0; e < I915_NUM_ENGINES; e++) {
+		INIT_LIST_HEAD(&scheduler->node_queue[e]);
+		scheduler->counts[e].flying = 0;
+		scheduler->counts[e].queued = 0;
+	}
+
+	/* Default tuning values: */
+	scheduler->priority_level_min     = -1023;
+	scheduler->priority_level_max     = 1023;
+	scheduler->priority_level_bump    = 50;
+	scheduler->priority_level_preempt = 900;
+	scheduler->min_flying             = 2;
+
+	dev_priv->scheduler = scheduler;
+
+	return 0;
+}
+
+/**
+ * i915_scheduler_destroy - Get rid of the scheduler.
+ * @dev: DRM device
+ */
+void i915_scheduler_destroy(struct drm_i915_private *dev_priv)
+{
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	int e;
+
+	if (!scheduler)
+		return;
+
+	for (e = 0; e < I915_NUM_ENGINES; e++)
+		WARN(!list_empty(&scheduler->node_queue[e]), "Destroying with list entries on engine %d!", e);
+
+	kfree(scheduler);
+	dev_priv->scheduler = NULL;
+}
+
+/*
+ * Add a popped node back in to the queue. For example, because the engine
+ * was hung when execfinal() was called and thus the engine submission needs
+ * to be retried later.
+ */
+static void i915_scheduler_node_requeue(struct i915_scheduler *scheduler,
+					struct i915_scheduler_queue_entry *node)
+{
+	WARN_ON(!I915_SQS_IS_FLYING(node));
+
+	/* Seqno will be reassigned on relaunch */
+	node->params.request->seqno = 0;
+	node->status = I915_SQS_QUEUED;
+	scheduler->counts[node->params.engine->id].flying--;
+	scheduler->counts[node->params.engine->id].queued++;
+}
+
+/*
+ * Give up on a node completely. For example, because it is causing the
+ * engine to hang or is using some resource that no longer exists.
+ */
+static void i915_scheduler_node_kill(struct i915_scheduler *scheduler,
+				     struct i915_scheduler_queue_entry *node)
+{
+	WARN_ON(I915_SQS_IS_COMPLETE(node));
+
+	if (I915_SQS_IS_FLYING(node))
+		scheduler->counts[node->params.engine->id].flying--;
+	else
+		scheduler->counts[node->params.engine->id].queued--;
+
+	node->status = I915_SQS_DEAD;
+}
+
+/* Mark a node as in flight on the hardware. */
+static void i915_scheduler_node_fly(struct i915_scheduler_queue_entry *node)
+{
+	struct drm_i915_private *dev_priv = to_i915(node->params.dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	struct intel_engine_cs *engine = node->params.engine;
+
+	assert_scheduler_lock_held(scheduler);
+
+	WARN_ON(node->status != I915_SQS_POPPED);
+
+	/*
+	 * Add the node (which should currently be in state popped) to the
+	 * front of the queue. This ensure that flying nodes are always held
+	 * in hardware submission order.
+	 */
+	list_add(&node->link, &scheduler->node_queue[engine->id]);
+
+	node->status = I915_SQS_FLYING;
+
+	scheduler->counts[engine->id].flying++;
+
+	if (!(scheduler->flags[engine->id] & I915_SF_INTERRUPTS_ENABLED)) {
+		bool success = true;
+
+		success = engine->irq_get(engine);
+		if (success)
+			scheduler->flags[engine->id] |= I915_SF_INTERRUPTS_ENABLED;
+	}
+}
+
+static inline uint32_t i915_scheduler_count_flying(struct i915_scheduler *scheduler,
+					    struct intel_engine_cs *engine)
+{
+	return scheduler->counts[engine->id].flying;
+}
+
+static void i915_scheduler_priority_bump_clear(struct i915_scheduler *scheduler)
+{
+	struct i915_scheduler_queue_entry *node;
+	int i;
+
+	assert_scheduler_lock_held(scheduler);
+
+	/*
+	 * Ensure circular dependencies don't cause problems and that a bump
+	 * by object usage only bumps each using buffer once:
+	 */
+	for (i = 0; i < I915_NUM_ENGINES; i++) {
+		for_each_scheduler_node(node, i)
+			node->bumped = false;
+	}
+}
+
+static int i915_scheduler_priority_bump(struct i915_scheduler *scheduler,
+				struct i915_scheduler_queue_entry *target,
+				uint32_t bump)
+{
+	uint32_t new_priority;
+	int i, count;
+
+	if (target->priority >= scheduler->priority_level_max)
+		return 1;
+
+	if (target->bumped)
+		return 0;
+
+	new_priority = target->priority + bump;
+	if ((new_priority <= target->priority) ||
+	    (new_priority > scheduler->priority_level_max))
+		target->priority = scheduler->priority_level_max;
+	else
+		target->priority = new_priority;
+
+	count = 1;
+	target->bumped = true;
+
+	for (i = 0; i < target->num_deps; i++) {
+		if (!target->dep_list[i])
+			continue;
+
+		if (target->dep_list[i]->bumped)
+			continue;
+
+		count += i915_scheduler_priority_bump(scheduler,
+						      target->dep_list[i],
+						      bump);
+	}
+
+	return count;
+}
+
+/*
+ * Nodes are considered valid dependencies if they are queued on any engine
+ * or if they are in flight on a different engine. In flight on the same
+ * engine is no longer interesting for non-premptive nodes as the engine
+ * serialises execution. For pre-empting nodes, all in flight dependencies
+ * are valid as they must not be jumped by the act of pre-empting.
+ *
+ * Anything that is neither queued nor flying is uninteresting.
+ */
+static inline bool i915_scheduler_is_dependency_valid(
+			struct i915_scheduler_queue_entry *node, uint32_t idx)
+{
+	struct i915_scheduler_queue_entry *dep;
+
+	dep = node->dep_list[idx];
+	if (!dep)
+		return false;
+
+	if (I915_SQS_IS_QUEUED(dep))
+		return true;
+
+	if (I915_SQS_IS_FLYING(dep)) {
+		if (node->params.engine != dep->params.engine)
+			return true;
+	}
+
+	return false;
+}
+
+static int i915_scheduler_pop_from_queue_locked(struct intel_engine_cs *engine,
+				struct i915_scheduler_queue_entry **pop_node)
+{
+	struct drm_i915_private *dev_priv = to_i915(engine->dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	struct i915_scheduler_queue_entry *best = NULL;
+	struct i915_scheduler_queue_entry *node;
+	int ret;
+	int i;
+	bool any_queued = false;
+	bool has_local, has_remote, only_remote = false;
+
+	assert_scheduler_lock_held(scheduler);
+
+	*pop_node = NULL;
+	ret = -ENODATA;
+
+	for_each_scheduler_node(node, engine->id) {
+		if (!I915_SQS_IS_QUEUED(node))
+			continue;
+		any_queued = true;
+
+		has_local  = false;
+		has_remote = false;
+		for (i = 0; i < node->num_deps; i++) {
+			if (!i915_scheduler_is_dependency_valid(node, i))
+				continue;
+
+			if (node->dep_list[i]->params.engine == node->params.engine)
+				has_local = true;
+			else
+				has_remote = true;
+		}
+
+		if (has_remote && !has_local)
+			only_remote = true;
+
+		if (!has_local && !has_remote) {
+			if (!best ||
+			    (node->priority > best->priority))
+				best = node;
+		}
+	}
+
+	if (best) {
+		list_del(&best->link);
+
+		INIT_LIST_HEAD(&best->link);
+		best->status = I915_SQS_POPPED;
+
+		scheduler->counts[engine->id].queued--;
+
+		ret = 0;
+	} else {
+		/* Can only get here if:
+		 * (a) there are no buffers in the queue
+		 * (b) all queued buffers are dependent on other buffers
+		 *     e.g. on a buffer that is in flight on a different engine
+		 */
+		if (only_remote) {
+			/* The only dependent buffers are on another engine. */
+			ret = -EAGAIN;
+		} else if (any_queued) {
+			/* It seems that something has gone horribly wrong! */
+			WARN_ONCE(true, "Broken dependency tracking on engine %d!\n",
+				  (int) engine->id);
+		}
+	}
+
+	*pop_node = best;
+	return ret;
+}
+
+/*
+ * NB: The driver mutex lock must be held before calling this function. It is
+ * only really required during the actual back end submission call. However,
+ * attempting to acquire a mutex while holding a spin lock is a Bad Idea.
+ * And releasing the one before acquiring the other leads to other code
+ * being run and interfering.
+ */
+static int i915_scheduler_submit(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = to_i915(engine->dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	struct i915_scheduler_queue_entry *node;
+	int ret, count = 0, flying;
+
+	WARN_ON(!mutex_is_locked(&engine->dev->struct_mutex));
+
+	spin_lock_irq(&scheduler->lock);
+
+	WARN_ON(scheduler->flags[engine->id] & I915_SF_SUBMITTING);
+	scheduler->flags[engine->id] |= I915_SF_SUBMITTING;
+
+	/* First time around, complain if anything unexpected occurs: */
+	ret = i915_scheduler_pop_from_queue_locked(engine, &node);
+	if (ret)
+		goto error;
+
+	do {
+		WARN_ON(node->params.engine != engine);
+		WARN_ON(node->status != I915_SQS_POPPED);
+		count++;
+
+		/*
+		 * The call to pop above will have removed the node from the
+		 * list. So add it back in and mark it as in flight.
+		 */
+		i915_scheduler_node_fly(node);
+
+		spin_unlock_irq(&scheduler->lock);
+		ret = dev_priv->gt.execbuf_final(&node->params);
+		spin_lock_irq(&scheduler->lock);
+
+		/*
+		 * Handle failed submission but first check that the
+		 * watchdog/reset code has not nuked the node while we
+		 * weren't looking:
+		 */
+		if (ret && (node->status != I915_SQS_DEAD)) {
+			bool requeue = true;
+
+			/*
+			 * Oh dear! Either the node is broken or the engine is
+			 * busy. So need to kill the node or requeue it and try
+			 * again later as appropriate.
+			 */
+
+			switch (-ret) {
+			case ENODEV:
+			case ENOENT:
+				/* Fatal errors. Kill the node. */
+				requeue = false;
+				i915_scheduler_node_kill(scheduler, node);
+				break;
+
+			case EAGAIN:
+			case EBUSY:
+			case EIO:
+			case ENOMEM:
+			case ERESTARTSYS:
+			case EINTR:
+				/* Supposedly recoverable errors. */
+				break;
+
+			default:
+				/*
+				 * Assume the error is recoverable and hope
+				 * for the best.
+				 */
+				MISSING_CASE(-ret);
+				break;
+			}
+
+			if (requeue) {
+				i915_scheduler_node_requeue(scheduler, node);
+				/*
+				 * No point spinning if the engine is currently
+				 * unavailable so just give up and come back
+				 * later.
+				 */
+				break;
+			}
+		}
+
+		/* Keep launching until the sky is sufficiently full. */
+		flying = i915_scheduler_count_flying(scheduler, engine);
+		if (flying >= scheduler->min_flying)
+			break;
+
+		/* Grab another node and go round again... */
+		ret = i915_scheduler_pop_from_queue_locked(engine, &node);
+	} while (ret == 0);
+
+	/* Don't complain about not being able to submit extra entries */
+	if (ret == -ENODATA)
+		ret = 0;
+
+	/*
+	 * Bump the priority of everything that was not submitted to prevent
+	 * starvation of low priority tasks by a spamming high priority task.
+	 */
+	i915_scheduler_priority_bump_clear(scheduler);
+	for_each_scheduler_node(node, engine->id) {
+		if (!I915_SQS_IS_QUEUED(node))
+			continue;
+
+		i915_scheduler_priority_bump(scheduler, node,
+					     scheduler->priority_level_bump);
+	}
+
+	/* On success, return the number of buffers submitted. */
+	if (ret == 0)
+		ret = count;
+
+error:
+	scheduler->flags[engine->id] &= ~I915_SF_SUBMITTING;
+	spin_unlock_irq(&scheduler->lock);
+	return ret;
+}
+
+static void i915_generate_dependencies(struct i915_scheduler *scheduler,
+				       struct i915_scheduler_queue_entry *node,
+				       uint32_t engine)
+{
+	struct i915_scheduler_obj_entry *this, *that;
+	struct i915_scheduler_queue_entry *test;
+	int i, j;
+	bool found;
+
+	for_each_scheduler_node(test, engine) {
+		if (I915_SQS_IS_COMPLETE(test))
+			continue;
+
+		/*
+		 * Batches on the same engine for the same
+		 * context must be kept in order.
+		 */
+		found = (node->params.ctx == test->params.ctx) &&
+			(node->params.engine == test->params.engine);
+
+		/*
+		 * Batches working on the same objects must
+		 * be kept in order.
+		 */
+		for (i = 0; (i < node->num_objs) && !found; i++) {
+			this = node->objs + i;
+
+			for (j = 0; j < test->num_objs; j++) {
+				that = test->objs + j;
+
+				if (this->obj != that->obj)
+					continue;
+
+				/* Only need to worry about writes */
+				if (this->read_only && that->read_only)
+					continue;
+
+				found = true;
+				break;
+			}
+		}
+
+		if (found) {
+			node->dep_list[node->num_deps] = test;
+			node->num_deps++;
+		}
+	}
+}
+
+static int i915_scheduler_queue_execbuffer_bypass(struct i915_scheduler_queue_entry *qe)
+{
+	struct drm_i915_private *dev_priv = to_i915(qe->params.dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	int ret;
+
+	scheduler->flags[qe->params.engine->id] |= I915_SF_SUBMITTING;
+	ret = dev_priv->gt.execbuf_final(&qe->params);
+	scheduler->flags[qe->params.engine->id] &= ~I915_SF_SUBMITTING;
+
+	/*
+	 * Don't do any clean up on failure because the caller will
+	 * do it all anyway.
+	 */
+	if (ret)
+		return ret;
+
+	/* Need to release any resources held by the node: */
+	qe->status = I915_SQS_COMPLETE;
+	i915_scheduler_clean_node(qe);
+
+	return 0;
+}
+
+static inline uint32_t i915_scheduler_count_incomplete(struct i915_scheduler *scheduler)
+{
+	int e, incomplete = 0;
+
+	for (e = 0; e < I915_NUM_ENGINES; e++)
+		incomplete += scheduler->counts[e].queued + scheduler->counts[e].flying;
+
+	return incomplete;
+}
+
+/**
+ * i915_scheduler_queue_execbuffer - Submit a batch buffer request to the
+ * scheduler.
+ * @qe: The batch buffer request to be queued.
+ * The expectation is the qe passed in is a local stack variable. This
+ * function will copy its contents into a freshly allocated list node. The
+ * new node takes ownership of said contents so the original qe should simply
+ * be discarded and not cleaned up (i.e. don't free memory it points to or
+ * dereference objects it holds). The node is added to the scheduler's queue
+ * and the batch buffer will be submitted to the hardware at some future
+ * point in time (which may be immediately, before returning or may be quite
+ * a lot later).
+ */
+int i915_scheduler_queue_execbuffer(struct i915_scheduler_queue_entry *qe)
+{
+	struct drm_i915_private *dev_priv = to_i915(qe->params.dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	struct intel_engine_cs *engine = qe->params.engine;
+	struct i915_scheduler_queue_entry *node;
+	bool not_flying;
+	int i, e;
+	int incomplete;
+
+	/* Bypass the scheduler and send the buffer immediately? */
+	if (1/*!i915.enable_scheduler*/)
+		return i915_scheduler_queue_execbuffer_bypass(qe);
+
+	node = kmalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return -ENOMEM;
+
+	*node = *qe;
+	INIT_LIST_HEAD(&node->link);
+	node->status = I915_SQS_QUEUED;
+	node->stamp  = jiffies;
+	i915_gem_request_reference(node->params.request);
+
+	WARN_ON(node->params.request->scheduler_qe);
+	node->params.request->scheduler_qe = node;
+
+	/*
+	 * Need to determine the number of incomplete entries in the list as
+	 * that will be the maximum size of the dependency list.
+	 *
+	 * Note that the allocation must not be made with the spinlock acquired
+	 * as kmalloc can sleep. However, the unlock/relock is safe because no
+	 * new entries can be queued up during the unlock as the i915 driver
+	 * mutex is still held. Entries could be removed from the list but that
+	 * just means the dep_list will be over-allocated which is fine.
+	 */
+	spin_lock_irq(&scheduler->lock);
+	incomplete = i915_scheduler_count_incomplete(scheduler);
+
+	/* Temporarily unlock to allocate memory: */
+	spin_unlock_irq(&scheduler->lock);
+	if (incomplete) {
+		node->dep_list = kmalloc_array(incomplete,
+					       sizeof(*node->dep_list),
+					       GFP_KERNEL);
+		if (!node->dep_list) {
+			kfree(node);
+			return -ENOMEM;
+		}
+	} else
+		node->dep_list = NULL;
+
+	spin_lock_irq(&scheduler->lock);
+	node->num_deps = 0;
+
+	if (node->dep_list) {
+		for (e = 0; e < I915_NUM_ENGINES; e++)
+			i915_generate_dependencies(scheduler, node, e);
+
+		WARN_ON(node->num_deps > incomplete);
+	}
+
+	node->priority = clamp(node->priority,
+			       scheduler->priority_level_min,
+			       scheduler->priority_level_max);
+
+	if ((node->priority > 0) && node->num_deps) {
+		i915_scheduler_priority_bump_clear(scheduler);
+
+		for (i = 0; i < node->num_deps; i++)
+			i915_scheduler_priority_bump(scheduler,
+					node->dep_list[i], node->priority);
+	}
+
+	list_add_tail(&node->link, &scheduler->node_queue[engine->id]);
+
+	not_flying = i915_scheduler_count_flying(scheduler, engine) <
+						 scheduler->min_flying;
+
+	scheduler->counts[engine->id].queued++;
+
+	spin_unlock_irq(&scheduler->lock);
+
+	if (not_flying)
+		i915_scheduler_submit(engine);
+
+	return 0;
+}
+
+/**
+ * i915_scheduler_notify_request - Notify the scheduler that the given
+ * request has completed on the hardware.
+ * @req: Request structure which has completed
+ * @preempt: Did it complete pre-emptively?
+ * A sequence number has popped out of the hardware and the request handling
+ * code has mapped it back to a request and will mark that request complete.
+ * It also calls this function to notify the scheduler about the completion
+ * so the scheduler's node can be updated appropriately.
+ * Returns true if the request is scheduler managed, false if not. The return
+ * value is combined for all freshly completed requests and if any were true
+ * then i915_scheduler_wakeup() is called so the scheduler can do further
+ * processing (submit more work) at the end.
+ */
+bool i915_scheduler_notify_request(struct drm_i915_gem_request *req)
+{
+	struct drm_i915_private *dev_priv = to_i915(req->engine->dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	struct i915_scheduler_queue_entry *node = req->scheduler_qe;
+	unsigned long flags;
+
+	if (!node)
+		return false;
+
+	spin_lock_irqsave(&scheduler->lock, flags);
+
+	WARN_ON(!I915_SQS_IS_FLYING(node));
+
+	/* Node was in flight so mark it as complete. */
+	if (req->cancelled)
+		node->status = I915_SQS_DEAD;
+	else
+		node->status = I915_SQS_COMPLETE;
+
+	scheduler->counts[req->engine->id].flying--;
+
+	spin_unlock_irqrestore(&scheduler->lock, flags);
+
+	return true;
+}
+
+static int i915_scheduler_remove_dependent(struct i915_scheduler *scheduler,
+				struct i915_scheduler_queue_entry *remove)
+{
+	struct i915_scheduler_queue_entry *node;
+	int i, r;
+	int count = 0;
+
+	/*
+	 * Ensure that a node is not being removed which is still dependent
+	 * upon other (not completed) work. If that happens, it implies
+	 * something has gone very wrong with the dependency tracking! Note
+	 * that there is no need to worry if this node has been explicitly
+	 * killed for some reason - it might be being killed before it got
+	 * sent to the hardware.
+	 */
+	if (remove->status != I915_SQS_DEAD) {
+		for (i = 0; i < remove->num_deps; i++)
+			if ((remove->dep_list[i]) &&
+			    (!I915_SQS_IS_COMPLETE(remove->dep_list[i])))
+				count++;
+		WARN_ON(count);
+	}
+
+	/*
+	 * Remove this node from the dependency lists of any other node which
+	 * might be waiting on it.
+	 */
+	for (r = 0; r < I915_NUM_ENGINES; r++) {
+		for_each_scheduler_node(node, r) {
+			for (i = 0; i < node->num_deps; i++) {
+				if (node->dep_list[i] != remove)
+					continue;
+
+				node->dep_list[i] = NULL;
+			}
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * i915_scheduler_wakeup - wake the scheduler's worker thread
+ * @dev: DRM device
+ * Called at the end of seqno interrupt processing if any request has
+ * completed that corresponds to a scheduler node.
+ */
+void i915_scheduler_wakeup(struct drm_device *dev)
+{
+	/* XXX: Need to call i915_scheduler_remove() via work handler. */
+}
+
+/**
+ * i915_scheduler_clean_node - free up any allocations/references
+ * associated with the given scheduler queue entry.
+ * @node: Queue entry structure which is complete
+ * After a give batch buffer completes on the hardware, all the information
+ * required to resubmit it is no longer required. However, the node entry
+ * itself might still be required for tracking purposes for a while longer.
+ * This function should be called as soon as the node is known to be complete
+ * so that these resources may be freed even though the node itself might
+ * hang around.
+ */
+void i915_scheduler_clean_node(struct i915_scheduler_queue_entry *node)
+{
+	if (!I915_SQS_IS_COMPLETE(node)) {
+		WARN(!node->params.request->cancelled,
+		     "Cleaning active node: %d!\n", node->status);
+		return;
+	}
+
+	if (node->params.batch_obj) {
+		/*
+		 * The batch buffer must be unpinned before it is unreferenced
+		 * otherwise the unpin fails with a missing vma!?
+		 */
+		if (node->params.dispatch_flags & I915_DISPATCH_SECURE)
+			i915_gem_execbuf_release_batch_obj(node->params.batch_obj);
+
+		node->params.batch_obj = NULL;
+	}
+
+	/* And anything else owned by the node: */
+	if (node->params.cliprects) {
+		kfree(node->params.cliprects);
+		node->params.cliprects = NULL;
+	}
+}
+
+static bool i915_scheduler_remove(struct i915_scheduler *scheduler,
+				  struct intel_engine_cs *engine,
+				  struct list_head *remove)
+{
+	struct i915_scheduler_queue_entry *node, *node_next;
+	bool do_submit;
+
+	spin_lock_irq(&scheduler->lock);
+
+	INIT_LIST_HEAD(remove);
+	list_for_each_entry_safe(node, node_next, &scheduler->node_queue[engine->id], link) {
+		if (!I915_SQS_IS_COMPLETE(node))
+			break;
+
+		list_del(&node->link);
+		list_add(&node->link, remove);
+
+		/* Strip the dependency info while the mutex is still locked */
+		i915_scheduler_remove_dependent(scheduler, node);
+
+		continue;
+	}
+
+	/*
+	 * Release the interrupt reference count if there are no longer any
+	 * nodes to worry about.
+	 */
+	if (list_empty(&scheduler->node_queue[engine->id]) &&
+	    (scheduler->flags[engine->id] & I915_SF_INTERRUPTS_ENABLED)) {
+		engine->irq_put(engine);
+		scheduler->flags[engine->id] &= ~I915_SF_INTERRUPTS_ENABLED;
+	}
+
+	/* Launch more packets now? */
+	do_submit = (scheduler->counts[engine->id].queued > 0) &&
+		    (scheduler->counts[engine->id].flying < scheduler->min_flying);
+
+	spin_unlock_irq(&scheduler->lock);
+
+	return do_submit;
+}
+
+void i915_scheduler_process_work(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = to_i915(engine->dev);
+	struct i915_scheduler *scheduler = dev_priv->scheduler;
+	struct i915_scheduler_queue_entry *node;
+	bool do_submit;
+	struct list_head remove;
+
+	if (list_empty(&scheduler->node_queue[engine->id]))
+		return;
+
+	/* Remove completed nodes. */
+	do_submit = i915_scheduler_remove(scheduler, engine, &remove);
+
+	if (!do_submit && list_empty(&remove))
+		return;
+
+	/* Need to grab the pm lock outside of the mutex lock */
+	if (do_submit)
+		intel_runtime_pm_get(dev_priv);
+
+	mutex_lock(&engine->dev->struct_mutex);
+
+	if (do_submit)
+		i915_scheduler_submit(engine);
+
+	while (!list_empty(&remove)) {
+		node = list_first_entry(&remove, typeof(*node), link);
+		list_del(&node->link);
+
+		/* Free up all the DRM references */
+		i915_scheduler_clean_node(node);
+
+		/* And anything else owned by the node: */
+		node->params.request->scheduler_qe = NULL;
+		i915_gem_request_unreference(node->params.request);
+		kfree(node->dep_list);
+		kfree(node);
+	}
+
+	mutex_unlock(&engine->dev->struct_mutex);
+
+	if (do_submit)
+		intel_runtime_pm_put(dev_priv);
+}
diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h
new file mode 100644
index 000000000000..c895c4cbc68e
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_scheduler.h
@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 2014 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#ifndef _I915_SCHEDULER_H_
+#define _I915_SCHEDULER_H_
+
+enum i915_scheduler_queue_status {
+	/* Limbo: */
+	I915_SQS_NONE = 0,
+	/* Not yet submitted to hardware: */
+	I915_SQS_QUEUED,
+	/* Popped from queue, ready to fly: */
+	I915_SQS_POPPED,
+	/* Sent to hardware for processing: */
+	I915_SQS_FLYING,
+	/* Finished processing on the hardware: */
+	I915_SQS_COMPLETE,
+	/* Killed by watchdog or catastrophic submission failure: */
+	I915_SQS_DEAD,
+	/* Limit value for use with arrays/loops */
+	I915_SQS_MAX
+};
+
+#define I915_SQS_IS_QUEUED(node)	(((node)->status == I915_SQS_QUEUED))
+#define I915_SQS_IS_FLYING(node)	(((node)->status == I915_SQS_FLYING))
+#define I915_SQS_IS_COMPLETE(node)	(((node)->status == I915_SQS_COMPLETE) || \
+					 ((node)->status == I915_SQS_DEAD))
+
+struct i915_scheduler_obj_entry {
+	struct drm_i915_gem_object *obj;
+	bool read_only;
+};
+
+struct i915_scheduler_queue_entry {
+	/* Any information required to submit this batch buffer to the hardware */
+	struct i915_execbuffer_params params;
+
+	/* -1023 = lowest priority, 0 = default, 1023 = highest */
+	int32_t priority;
+	bool bumped;
+
+	/* Objects referenced by this batch buffer */
+	struct i915_scheduler_obj_entry *objs;
+	int num_objs;
+
+	/* Batch buffers this one is dependent upon */
+	struct i915_scheduler_queue_entry **dep_list;
+	int num_deps;
+
+	enum i915_scheduler_queue_status status;
+	unsigned long stamp;
+
+	/* List of all scheduler queue entry nodes */
+	struct list_head link;
+};
+
+struct i915_scheduler_node_states {
+	uint32_t flying;
+	uint32_t queued;
+};
+
+struct i915_scheduler {
+	struct list_head node_queue[I915_NUM_ENGINES];
+	uint32_t flags[I915_NUM_ENGINES];
+	spinlock_t lock;
+
+	/* Node counts: */
+	struct i915_scheduler_node_states counts[I915_NUM_ENGINES];
+
+	/* Tuning parameters: */
+	int32_t priority_level_min;
+	int32_t priority_level_max;
+	int32_t priority_level_bump;
+	int32_t priority_level_preempt;
+	uint32_t min_flying;
+};
+
+/* Flag bits for i915_scheduler::flags */
+enum {
+	I915_SF_INTERRUPTS_ENABLED  = (1 << 0),
+	I915_SF_SUBMITTING          = (1 << 1),
+};
+
+bool i915_scheduler_is_enabled(struct drm_device *dev);
+int i915_scheduler_init(struct drm_device *dev);
+void i915_scheduler_destroy(struct drm_i915_private *dev_priv);
+void i915_scheduler_clean_node(struct i915_scheduler_queue_entry *node);
+int i915_scheduler_queue_execbuffer(struct i915_scheduler_queue_entry *qe);
+bool i915_scheduler_notify_request(struct drm_i915_gem_request *req);
+void i915_scheduler_wakeup(struct drm_device *dev);
+
+#endif  /* _I915_SCHEDULER_H_ */