[PATCH 10/10] drm/i915/scheduler: Boost priorities for flips

[Chris Wilson]

Boost the priority of any rendering required to show the next pageflip
as we want to avoid missing the vblank by being delayed by invisible
workload. We prioritise avoiding jank and jitter in the GUI over
starving background tasks.

v2: Descend dma_fence_array when boosting priorities.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h      |  5 +++
 drivers/gpu/drm/i915/i915_gem.c      | 65 ++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_display.c |  2 ++
 3 files changed, 72 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index fa8ee8738e7c..4e7148a3ee8b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3093,6 +3093,11 @@ int i915_gem_object_wait(struct drm_i915_gem_object *obj,
 			 unsigned int flags,
 			 long timeout,
 			 struct intel_rps_client *rps);
+int i915_gem_object_wait_priority(struct drm_i915_gem_object *obj,
+				  unsigned int flags,
+				  int priority);
+#define I915_PRIORITY_DISPLAY I915_PRIORITY_MAX
+
 int __must_check
 i915_gem_object_set_to_gtt_domain(struct drm_i915_gem_object *obj,
 				  bool write);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 7a43f2a73552..3fb5e66e4d65 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -34,6 +34,7 @@
 #include "intel_drv.h"
 #include "intel_frontbuffer.h"
 #include "intel_mocs.h"
+#include <linux/dma-fence-array.h>
 #include <linux/reservation.h>
 #include <linux/shmem_fs.h>
 #include <linux/slab.h>
@@ -434,6 +435,70 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 	return timeout;
 }
 
+static void __fence_set_priority(struct dma_fence *fence, int prio)
+{
+	struct drm_i915_gem_request *rq;
+	struct intel_engine_cs *engine;
+
+	if (!dma_fence_is_i915(fence))
+		return;
+
+	rq = to_request(fence);
+	engine = rq->engine;
+	if (!engine->schedule)
+		return;
+
+	engine->schedule(rq, prio);
+}
+
+static void fence_set_priority(struct dma_fence *fence, int prio)
+{
+	/* Recurse once into a fence-array */
+	if (dma_fence_is_array(fence)) {
+		struct dma_fence_array *array = to_dma_fence_array(fence);
+		int i;
+
+		for (i = 0; i < array->num_fences; i++)
+			__fence_set_priority(array->fences[i], prio);
+	} else {
+		__fence_set_priority(fence, prio);
+	}
+}
+
+int
+i915_gem_object_wait_priority(struct drm_i915_gem_object *obj,
+			      unsigned int flags,
+			      int prio)
+{
+	struct dma_fence *excl;
+
+	if (flags & I915_WAIT_ALL) {
+		struct dma_fence **shared;
+		unsigned int count, i;
+		int ret;
+
+		ret = reservation_object_get_fences_rcu(obj->resv,
+							&excl, &count, &shared);
+		if (ret)
+			return ret;
+
+		for (i = 0; i < count; i++) {
+			fence_set_priority(shared[i], prio);
+			dma_fence_put(shared[i]);
+		}
+
+		kfree(shared);
+	} else {
+		excl = reservation_object_get_excl_rcu(obj->resv);
+	}
+
+	if (excl) {
+		fence_set_priority(excl, prio);
+		dma_fence_put(excl);
+	}
+	return 0;
+}
+
 /**
  * Waits for rendering to the object to be completed
  * @obj: i915 gem object
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 072a0b1bc9da..33dceb2a2ec8 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -14783,6 +14783,8 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 						      GFP_KERNEL);
 		if (ret < 0)
 			return ret;
+
+		i915_gem_object_wait_priority(obj, 0, I915_PRIORITY_DISPLAY);
 	}
 
 	if (plane->type == DRM_PLANE_TYPE_CURSOR &&
-- 
2.10.2