From 193065024072c0d6f2972142d5df5a00b33324c6 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue, 15 Oct 2019 14:26:06 +0100
Subject: drm/i915: Flush tasklet submission before sleeping on
 i915_request_wait
Git-commit: 193065024072c0d6f2972142d5df5a00b33324c6
Patch-mainline: v5.5-rc1
References: bsc#1152489

If the system is being slow and userspace is racing ahead of the GPU and
finds itself waiting for the GPU to catch up, before the process sleeps
give the tasklet a kick, bypassing ksoftirqd. If the system is
overloaded, then ksoftirqd may be delayed incurring additional latency
to our user.

This should not be a frequent problem, but in the past we have observed
several hundred millisecond delays before ksoftirqd services an
interrupt, so burn a few cycles to lend a helping hand.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191015132606.14349-1-chris@chris-wilson.co.uk
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/i915/i915_request.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index b8a54572a4f8..f1cadad4e81c 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -1496,6 +1496,7 @@ long i915_request_wait(struct i915_request *rq,
 			break;
 		}
 
+		intel_engine_flush_submission(rq->engine);
 		timeout = io_schedule_timeout(timeout);
 	}
 	__set_current_state(TASK_RUNNING);
-- 
2.28.0