From 13ed13a4dcbf0b664acbf9e6f98ec7851cc59862 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 21 Oct 2019 09:02:11 +0100
Subject: drm/i915: Don't set queue_priority_hint if we don't kick the
 submission
Git-commit: 13ed13a4dcbf0b664acbf9e6f98ec7851cc59862
Patch-mainline: v5.5-rc1
References: bsc#1152489

If we change the priority of the active context, then it has no impact
on the decision of whether to preempt the active context -- we don't
preempt the context with itself. In this situation, we elide the tasklet
rescheduling and should *not* be marking up the queue_priority_hint as
that may mask a later submission where we decide we don't have to kick
the tasklet as a higher priority submission is pending (spoiler alert,
it was not).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021080226.537-1-chris@chris-wilson.co.uk
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/i915/i915_scheduler.c |   24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

--- a/drivers/gpu/drm/i915/i915_scheduler.c
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -193,8 +193,7 @@ static void kick_submission(struct intel
 			    const struct i915_request *rq,
 			    int prio)
 {
-	const struct i915_request *inflight =
-		execlists_active(&engine->execlists);
+	const struct i915_request *inflight;
 
 	/*
 	 * We only need to kick the tasklet once for the high priority
@@ -203,30 +202,21 @@ static void kick_submission(struct intel
 	if (prio <= engine->execlists.queue_priority_hint)
 		return;
 
-	rcu_read_lock();
-
 	/* Nothing currently active? We're overdue for a submission! */
+	inflight = execlists_active(&engine->execlists);
 	if (!inflight)
-		goto unlock;
+		return;
 
 	/*
 	 * If we are already the currently executing context, don't
-	 * bother evaluating if we should preempt ourselves, or if
-	 * we expect nothing to change as a result of running the
-	 * tasklet, i.e. we have not change the priority queue
-	 * sufficiently to oust the running context.
+	 * bother evaluating if we should preempt ourselves.
 	 */
 	if (inflight->hw_context == rq->hw_context)
-		goto unlock;
+		return;
 
 	engine->execlists.queue_priority_hint = prio;
-	if (inflight && need_preempt(prio, rq_prio(inflight)))
-		goto unlock;
-
-	tasklet_hi_schedule(&engine->execlists.tasklet);
-
-unlock:
-	rcu_read_unlock();
+	if (need_preempt(prio, rq_prio(inflight)))
+		tasklet_hi_schedule(&engine->execlists.tasklet);
 }
 
 static void __i915_schedule(struct i915_sched_node *node,