[PATCH] drm/i915: Look for active requests earlier in the reset path

[Michel Thierry <michel.thierry@intel.com>]

And store the active request so that we only search for it once; this
applies for reset-engine and full reset.

v2: Check for request completion inside _prepare_engine, don't use
ECANCELED, remove unnecessary null checks (Chris).

v3: Capture active requests during reset_prepare and store it the
engine hangcheck obj.

v4: Rename commit, change i915_gem_reset_request to just confirm the
active_request is still incomplete, instead of engine_stalled (Chris).

v5: With style; pass the active request to gem_reset_engine, keep single
return in reset_prepare_engine (Chris).

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c         | 14 ++++++------
 drivers/gpu/drm/i915/i915_drv.h         |  6 ++++--
 drivers/gpu/drm/i915/i915_gem.c         | 38 ++++++++++++++++++++-------------
 drivers/gpu/drm/i915/intel_ringbuffer.h |  1 +
 4 files changed, 36 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index d62793805794..2ba288e9311c 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1895,23 +1895,25 @@ int i915_reset_engine(struct intel_engine_cs *engine)
 	int ret;
 	struct drm_i915_private *dev_priv = engine->i915;
 	struct i915_gpu_error *error = &dev_priv->gpu_error;
+	struct drm_i915_gem_request *active_request;
 
 	GEM_BUG_ON(!test_bit(I915_RESET_ENGINE_IN_PROGRESS, &error->flags));
 
 	DRM_DEBUG_DRIVER("resetting %s\n", engine->name);
 
-	ret = i915_gem_reset_prepare_engine(engine);
-	if (ret) {
-		DRM_ERROR("Previous reset failed - promote to full reset\n");
+	active_request = i915_gem_reset_prepare_engine(engine);
+	if (IS_ERR(active_request)) {
+		DRM_DEBUG_DRIVER("Previous reset failed, promote to full reset\n");
+		ret = PTR_ERR(active_request);
 		goto out;
 	}
 
 	/*
-	 * the request that caused the hang is stuck on elsp, identify the
-	 * active request and drop it, adjust head to skip the offending
+	 * the request that caused the hang is stuck on elsp, we know the
+	 * active request and can drop it, adjust head to skip the offending
 	 * request to resume executing remaining requests in the queue.
 	 */
-	i915_gem_reset_engine(engine);
+	i915_gem_reset_engine(engine, active_request);
 
 	/* forcing engine to idle */
 	ret = intel_reset_engine_start(engine);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a5b9c666b3bf..f8cbd286f904 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3370,14 +3370,16 @@ static inline u32 i915_reset_count(struct i915_gpu_error *error)
 	return READ_ONCE(error->reset_count);
 }
 
-int i915_gem_reset_prepare_engine(struct intel_engine_cs *engine);
+struct drm_i915_gem_request *
+i915_gem_reset_prepare_engine(struct intel_engine_cs *engine);
 int i915_gem_reset_prepare(struct drm_i915_private *dev_priv);
 void i915_gem_reset(struct drm_i915_private *dev_priv);
 void i915_gem_reset_finish_engine(struct intel_engine_cs *engine);
 void i915_gem_reset_finish(struct drm_i915_private *dev_priv);
 void i915_gem_set_wedged(struct drm_i915_private *dev_priv);
 bool i915_gem_unset_wedged(struct drm_i915_private *dev_priv);
-void i915_gem_reset_engine(struct intel_engine_cs *engine);
+void i915_gem_reset_engine(struct intel_engine_cs *engine,
+			   struct drm_i915_gem_request *request);
 
 void i915_gem_init_mmio(struct drm_i915_private *i915);
 int __must_check i915_gem_init(struct drm_i915_private *dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index b5dc073a5ddc..6e14bf039aed 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2793,12 +2793,14 @@ static bool engine_stalled(struct intel_engine_cs *engine)
 	return true;
 }
 
-/* Ensure irq handler finishes, and not run again. */
-int i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
+/*
+ * Ensure irq handler finishes, and not run again.
+ * Also store the active request so that we only search for it once.
+ */
+struct drm_i915_gem_request *
+i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
 {
-	struct drm_i915_gem_request *request;
-	int err = 0;
-
+	struct drm_i915_gem_request *request = NULL;
 
 	/* Prevent the signaler thread from updating the request
 	 * state (by calling dma_fence_signal) as we are processing
@@ -2828,20 +2830,28 @@ int i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
 	if (engine_stalled(engine)) {
 		request = i915_gem_find_active_request(engine);
 		if (request && request->fence.error == -EIO)
-			err = -EIO; /* Previous reset failed! */
+			request = ERR_PTR(-EIO); /* Previous reset failed! */
 	}
 
-	return err;
+	return request;
 }
 
 int i915_gem_reset_prepare(struct drm_i915_private *dev_priv)
 {
 	struct intel_engine_cs *engine;
+	struct drm_i915_gem_request *request;
 	enum intel_engine_id id;
 	int err = 0;
 
-	for_each_engine(engine, dev_priv, id)
-		err = i915_gem_reset_prepare_engine(engine);
+	for_each_engine(engine, dev_priv, id) {
+		request = i915_gem_reset_prepare_engine(engine);
+		if (IS_ERR(request)) {
+			err = PTR_ERR(request);
+			break;
+		}
+
+		engine->hangcheck.active_request = request;
+	}
 
 	i915_gem_revoke_fences(dev_priv);
 
@@ -2894,7 +2904,7 @@ static void engine_skip_context(struct drm_i915_gem_request *request)
 static bool i915_gem_reset_request(struct drm_i915_gem_request *request)
 {
 	/* Read once and return the resolution */
-	const bool guilty = engine_stalled(request->engine);
+	const bool guilty = !i915_gem_request_completed(request);
 
 	/* The guilty request will get skipped on a hung engine.
 	 *
@@ -2928,11 +2938,9 @@ static bool i915_gem_reset_request(struct drm_i915_gem_request *request)
 	return guilty;
 }
 
-void i915_gem_reset_engine(struct intel_engine_cs *engine)
+void i915_gem_reset_engine(struct intel_engine_cs *engine,
+			   struct drm_i915_gem_request *request)
 {
-	struct drm_i915_gem_request *request;
-
-	request = i915_gem_find_active_request(engine);
 	if (request && i915_gem_reset_request(request)) {
 		DRM_DEBUG_DRIVER("resetting %s to restart from tail of request 0x%x\n",
 				 engine->name, request->global_seqno);
@@ -2958,7 +2966,7 @@ void i915_gem_reset(struct drm_i915_private *dev_priv)
 	for_each_engine(engine, dev_priv, id) {
 		struct i915_gem_context *ctx;
 
-		i915_gem_reset_engine(engine);
+		i915_gem_reset_engine(engine, engine->hangcheck.active_request);
 		ctx = fetch_and_zero(&engine->last_retired_context);
 		if (ctx)
 			engine->context_unpin(engine, ctx);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index ec16fb6fde62..f850c4b12337 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -121,6 +121,7 @@ struct intel_engine_hangcheck {
 	unsigned long action_timestamp;
 	int deadlock;
 	struct intel_instdone instdone;
+	struct drm_i915_gem_request *active_request;
 	bool stalled;
 };
 
-- 
2.11.0

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