drm/i915: Move object backing storage manipulation to its own locking

Break the allocation of the backing storage away from struct_mutex into
a per-object lock. This allows parallel page allocation, provided we can
do so outside of struct_mutex (i.e. set-domain-ioctl, pwrite, GTT
fault), i.e. before execbuf! The increased cost of the atomic counters
are hidden behind i915_vma_pin() for the typical case of execbuf, i.e.
as the object is typically bound between execbufs, the page_pin_count is
static. The cost will be felt around set-domain and pwrite, but offset
by the improvement from reduced struct_mutex contention.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-14-chris@chris-wilson.co.uk

1 files changed, 34 insertions, 17 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index f95061faeae6..c8a4c40ec2c2 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -48,6 +48,20 @@ static bool mutex_is_locked_by(struct mutex *mutex, struct task_struct *task)
 #endif
 }
 
+static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
+{
+	if (!mutex_trylock(&dev->struct_mutex)) {
+		if (!mutex_is_locked_by(&dev->struct_mutex, current))
+			return false;
+
+		*unlock = false;
+	} else {
+		*unlock = true;
+	}
+
+	return true;
+}
+
 static bool any_vma_pinned(struct drm_i915_gem_object *obj)
 {
 	struct i915_vma *vma;
@@ -66,6 +80,9 @@ static bool swap_available(void)
 
 static bool can_release_pages(struct drm_i915_gem_object *obj)
 {
+	if (!obj->mm.pages)
+		return false;
+
 	/* Only shmemfs objects are backed by swap */
 	if (!obj->base.filp)
 		return false;
@@ -78,7 +95,7 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
 	 * to the GPU, simply unbinding from the GPU is not going to succeed
 	 * in releasing our pin count on the pages themselves.
 	 */
-	if (obj->mm.pages_pin_count > obj->bind_count)
+	if (atomic_read(&obj->mm.pages_pin_count) > obj->bind_count)
 		return false;
 
 	if (any_vma_pinned(obj))
@@ -95,7 +112,7 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj)
 {
 	if (i915_gem_object_unbind(obj) == 0)
 		__i915_gem_object_put_pages(obj);
-	return !obj->mm.pages;
+	return !READ_ONCE(obj->mm.pages);
 }
 
 /**
@@ -135,6 +152,10 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 		{ NULL, 0 },
 	}, *phase;
 	unsigned long count = 0;
+	bool unlock;
+
+	if (!i915_gem_shrinker_lock(&dev_priv->drm, &unlock))
+		return 0;
 
 	trace_i915_gem_shrink(dev_priv, target, flags);
 	i915_gem_retire_requests(dev_priv);
@@ -199,8 +220,14 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 
 			i915_gem_object_get(obj);
 
-			if (unsafe_drop_pages(obj))
-				count += obj->base.size >> PAGE_SHIFT;
+			if (unsafe_drop_pages(obj)) {
+				mutex_lock(&obj->mm.lock);
+				if (!obj->mm.pages) {
+					__i915_gem_object_invalidate(obj);
+					count += obj->base.size >> PAGE_SHIFT;
+				}
+				mutex_unlock(&obj->mm.lock);
+			}
 
 			i915_gem_object_put(obj);
 		}
@@ -211,6 +238,9 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 		intel_runtime_pm_put(dev_priv);
 
 	i915_gem_retire_requests(dev_priv);
+	if (unlock)
+		mutex_unlock(&dev_priv->drm.struct_mutex);
+
 	/* expedite the RCU grace period to free some request slabs */
 	synchronize_rcu_expedited();
 
@@ -244,19 +274,6 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv)
 	return freed;
 }
 
-static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
-{
-	if (!mutex_trylock(&dev->struct_mutex)) {
-		if (!mutex_is_locked_by(&dev->struct_mutex, current))
-			return false;
-
-		*unlock = false;
-	} else
-		*unlock = true;
-
-	return true;
-}
-
 static unsigned long
 i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 {