[PATCH 51/80] drm/i915: Use a preemption timeout to enforce interactivity

Chris Wilson chris at chris-wilson.co.uk
Thu Aug 2 10:28:56 UTC 2018


Use a liberal timeout of 20ms to ensure that the rendering for an
interactive pageflip is started in a timely fashion, and that
user interaction is not blocked by GPU, or CPU, hogs. This is at the cost
of resetting whoever was blocking the preemption, likely leading to that
context/process being banned from submitting future requests.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h      |  4 +++-
 drivers/gpu/drm/i915/i915_gem.c      | 19 +++++++++++--------
 drivers/gpu/drm/i915/intel_display.c | 17 ++++++++++++++++-
 3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 351e4bbce093..491d84b2bab7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3127,8 +3127,10 @@ int i915_gem_object_wait(struct drm_i915_gem_object *obj,
 			 struct intel_rps_client *rps);
 int i915_gem_object_wait_priority(struct drm_i915_gem_object *obj,
 				  unsigned int flags,
-				  const struct i915_sched_attr *attr);
+				  const struct i915_sched_attr *attr,
+				  unsigned int timeout);
 #define I915_PRIORITY_DISPLAY I915_USER_PRIORITY(I915_PRIORITY_MAX)
+#define I915_PREEMPTION_TIMEOUT_DISPLAY (100 * 1000 * 1000) /* 100 ms / 10Hz */
 
 int __must_check
 i915_gem_object_set_to_wc_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 0dd86e7eacab..fbe4518cfbac 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -554,7 +554,8 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 }
 
 static void __fence_set_priority(struct dma_fence *fence,
-				 const struct i915_sched_attr *attr)
+				 const struct i915_sched_attr *attr,
+				 unsigned int timeout)
 {
 	struct i915_request *rq;
 	struct intel_engine_cs *engine;
@@ -568,13 +569,14 @@ static void __fence_set_priority(struct dma_fence *fence,
 	local_bh_disable();
 	rcu_read_lock(); /* RCU serialisation for set-wedged protection */
 	if (engine->schedule)
-		engine->schedule(rq, attr, 0);
+		engine->schedule(rq, attr, timeout);
 	rcu_read_unlock();
 	local_bh_enable(); /* kick the tasklets if queues were reprioritised */
 }
 
 static void fence_set_priority(struct dma_fence *fence,
-			       const struct i915_sched_attr *attr)
+			       const struct i915_sched_attr *attr,
+			       unsigned int timeout)
 {
 	/* Recurse once into a fence-array */
 	if (dma_fence_is_array(fence)) {
@@ -582,16 +584,17 @@ static void fence_set_priority(struct dma_fence *fence,
 		int i;
 
 		for (i = 0; i < array->num_fences; i++)
-			__fence_set_priority(array->fences[i], attr);
+			__fence_set_priority(array->fences[i], attr, timeout);
 	} else {
-		__fence_set_priority(fence, attr);
+		__fence_set_priority(fence, attr, timeout);
 	}
 }
 
 int
 i915_gem_object_wait_priority(struct drm_i915_gem_object *obj,
 			      unsigned int flags,
-			      const struct i915_sched_attr *attr)
+			      const struct i915_sched_attr *attr,
+			      unsigned int timeout)
 {
 	struct dma_fence *excl;
 
@@ -606,7 +609,7 @@ i915_gem_object_wait_priority(struct drm_i915_gem_object *obj,
 			return ret;
 
 		for (i = 0; i < count; i++) {
-			fence_set_priority(shared[i], attr);
+			fence_set_priority(shared[i], attr, timeout);
 			dma_fence_put(shared[i]);
 		}
 
@@ -616,7 +619,7 @@ i915_gem_object_wait_priority(struct drm_i915_gem_object *obj,
 	}
 
 	if (excl) {
-		fence_set_priority(excl, attr);
+		fence_set_priority(excl, attr, timeout);
 		dma_fence_put(excl);
 	}
 	return 0;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 808c37050037..4ed3c2fdbbaa 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13000,7 +13000,8 @@ static void fb_obj_bump_render_priority(struct drm_i915_gem_object *obj)
 		.priority = I915_PRIORITY_DISPLAY,
 	};
 
-	i915_gem_object_wait_priority(obj, 0, &attr);
+	i915_gem_object_wait_priority(obj, 0,
+				      &attr, I915_PREEMPTION_TIMEOUT_DISPLAY);
 }
 
 /**
@@ -13079,6 +13080,20 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 
 	ret = intel_plane_pin_fb(to_intel_plane_state(new_state));
 
+	/*
+	 * Reschedule our dependencies, and ensure we run within a timeout.
+	 *
+	 * Note that if the timeout is exceeded, then whoever was running that
+	 * prevented us from acquiring the GPU is declared rogue and reset. An
+	 * unresponsive process will then be banned in order to preserve
+	 * interactivity. Since this can be seen as a bit heavy-handed, we
+	 * select a timeout for when the dropped frames start to become a
+	 * noticeable nuisance for the user (100 ms, i.e. preemption was
+	 * blocked for more than a few frames). Note, this is only a timeout
+	 * for a delay in preempting the current request in order to run our
+	 * dependency chain, our dependency chain may itself take a long time
+	 * to run to completion before we can present the framebuffer.
+	 */
 	fb_obj_bump_render_priority(obj);
 
 	mutex_unlock(&dev_priv->drm.struct_mutex);
-- 
2.18.0



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