linux-kernel - [PATCH] sched/deadline: Do not start hrtick if its disabled for DL

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Message-ID: <20241112012240.1887813-1-joel@joelfernandes.org>
Date: Tue, 12 Nov 2024 01:22:39 +0000
From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
To: linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
	Aashish Sharma <shraash@...gle.com>,
	Vineeth Pillai <vineeth@...byteword.org>
Subject: [PATCH] sched/deadline: Do not start hrtick if its disabled for DL

Fix an issue where high-resolution timers causes aggressive preemptions,
leading to increased idle times in CFS tasks (which are inside the DL
server). The problem was traced to improper usage of hrtick_enabled(),
which could start high-resolution ticks unexpectedly causing repeated
preemptions.

The fix replaces this call with hrtick_enabled_dl(), aligning it with
scheduler feature checks.

Reported-by: Aashish Sharma <shraash@...gle.com>
Reported-by: Vineeth Pillai <vineeth@...byteword.org>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/sched/deadline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index b216e6deeac4..d46502b9ce58 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2121,7 +2121,7 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
 	if (!p->dl_server)
 		set_next_task_dl(rq, p, true);
 
-	if (hrtick_enabled(rq))
+	if (hrtick_enabled_dl(rq))
 		start_hrtick_dl(rq, &p->dl);
 
 	return p;
-- 
2.47.0.277.g8800431eea-goog