linux-kernel - [PATCH 2/2 RESEND] sched/rt: sysctl_sched_rr_timeslice show default timeslice after reset

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Date:   Wed,  2 Aug 2023 17:19:06 +0200
From:   Cyril Hrubis <chrubis@...e.cz>
To:     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>,
        linux-kernel@...r.kernel.org
Cc:     ltp@...ts.linux.it, Cyril Hrubis <chrubis@...e.cz>,
        Jiri Bohac <jbohac@...e.cz>, Petr Vorel <pvorel@...e.cz>
Subject: [PATCH 2/2 RESEND] sched/rt: sysctl_sched_rr_timeslice show default timeslice after reset

The sched_rr_timeslice can be reset to default by writing value that is
<= 0. However after reading from this file we always got the last value
written, which is not useful at all.

$ echo -1 > /proc/sys/kernel/sched_rr_timeslice_ms
$ cat /proc/sys/kernel/sched_rr_timeslice_ms
-1

Fix this by setting the variable that holds the sysctl file value to the
jiffies_to_msecs(RR_TIMESLICE) in case that <= 0 value was written.

CC: Jiri Bohac <jbohac@...e.cz>
Signed-off-by: Cyril Hrubis <chrubis@...e.cz>
Acked-by: Mel Gorman <mgorman@...e.de>
Reviewed-by: Petr Vorel <pvorel@...e.cz>
Tested-by: Petr Vorel <pvorel@...e.cz>
---
 kernel/sched/rt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 185d3d749f6b..0597ba0f85ff 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -3062,6 +3062,9 @@ static int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
 		sched_rr_timeslice =
 			sysctl_sched_rr_timeslice <= 0 ? RR_TIMESLICE :
 			msecs_to_jiffies(sysctl_sched_rr_timeslice);
+
+		if (sysctl_sched_rr_timeslice <= 0)
+			sysctl_sched_rr_timeslice = jiffies_to_msecs(RR_TIMESLICE);
 	}
 	mutex_unlock(&mutex);
 
-- 
2.41.0