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.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Tested-by: Petr Vorel <pvorel@suse.cz>
Link: https://lore.kernel.org/r/20230802151906.25258-3-chrubis@suse.cz

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 185d3d7..0597ba0 100644 (file)
--- 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);