[Intel-gfx] [PATCH] drm/i915/gt: Flush submission tasklet before waiting/retiring

[Chris Wilson]

A common bane of ours is arbitrary delays in ksoftirqd processing our
submission tasklet. Give the submission tasklet a kick before we wait to
avoid those delays eating into a tight timeout.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_engine.h      |  3 +-
 drivers/gpu/drm/i915/gt/intel_engine_cs.c   | 33 +++++++++++++--------
 drivers/gpu/drm/i915/gt/intel_gt_requests.c | 12 ++++++++
 3 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
index c9e8c8ccbd47..d624752f2a92 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine.h
@@ -407,8 +407,9 @@ static inline void __intel_engine_reset(struct intel_engine_cs *engine,
 	engine->serial++; /* contexts lost */
 }
 
-bool intel_engine_is_idle(struct intel_engine_cs *engine);
 bool intel_engines_are_idle(struct intel_gt *gt);
+bool intel_engine_is_idle(struct intel_engine_cs *engine);
+void intel_engine_flush_submission(struct intel_engine_cs *engine);
 
 void intel_engines_reset_default_submission(struct intel_gt *gt);
 
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 6220b7151bb9..7e2aa7a6bef0 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -1040,6 +1040,25 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
 	return idle;
 }
 
+void intel_engine_flush_submission(struct intel_engine_cs *engine)
+{
+	struct tasklet_struct *t = &engine->execlists.tasklet;
+
+	if (__tasklet_is_scheduled(t)) {
+		local_bh_disable();
+		if (tasklet_trylock(t)) {
+			/* Must wait for any GPU reset in progress. */
+			if (__tasklet_is_enabled(t))
+				t->func(t->data);
+			tasklet_unlock(t);
+		}
+		local_bh_enable();
+	}
+
+	/* Otherwise flush the tasklet if it was running on another cpu */
+	tasklet_unlock_wait(t);
+}
+
 /**
  * intel_engine_is_idle() - Report if the engine has finished process all work
  * @engine: the intel_engine_cs
@@ -1058,21 +1077,9 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
 
 	/* Waiting to drain ELSP? */
 	if (execlists_active(&engine->execlists)) {
-		struct tasklet_struct *t = &engine->execlists.tasklet;
-
 		synchronize_hardirq(engine->i915->drm.pdev->irq);
 
-		local_bh_disable();
-		if (tasklet_trylock(t)) {
-			/* Must wait for any GPU reset in progress. */
-			if (__tasklet_is_enabled(t))
-				t->func(t->data);
-			tasklet_unlock(t);
-		}
-		local_bh_enable();
-
-		/* Otherwise flush the tasklet if it was on another cpu */
-		tasklet_unlock_wait(t);
+		intel_engine_flush_submission(engine);
 
 		if (execlists_active(&engine->execlists))
 			return false;
diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
index ca606b79fd5e..cbb4069b11e1 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
@@ -4,6 +4,7 @@
  * Copyright © 2019 Intel Corporation
  */
 
+#include "i915_drv.h" /* for_each_engine() */
 #include "i915_request.h"
 #include "intel_gt.h"
 #include "intel_gt_pm.h"
@@ -19,6 +20,15 @@ static void retire_requests(struct intel_timeline *tl)
 			break;
 }
 
+static void flush_submission(struct intel_gt *gt)
+{
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+
+	for_each_engine(engine, gt->i915, id)
+		intel_engine_flush_submission(engine);
+}
+
 long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
 {
 	struct intel_gt_timelines *timelines = &gt->timelines;
@@ -32,6 +42,8 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
 	if (unlikely(timeout < 0))
 		timeout = -timeout, interruptible = false;
 
+	flush_submission(gt); /* kick the ksoftirqd tasklets */
+
 	spin_lock_irqsave(&timelines->lock, flags);
 	list_for_each_entry_safe(tl, tn, &timelines->active_list, link) {
 		if (!mutex_trylock(&tl->mutex)) {
-- 
2.23.0