sched: tweak the sched_runtime_limit tunable

Michael Gerdau reported reniced task CPU usage weirdnesses.
Such symptoms can be caused by limit underruns so double the
sched_runtime_limit.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c
index a4b22d9..96e9b82 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4923,7 +4923,7 @@
 	if (sysctl_sched_granularity > gran_limit)
 		sysctl_sched_granularity = gran_limit;
 
-	sysctl_sched_runtime_limit = sysctl_sched_granularity * 4;
+	sysctl_sched_runtime_limit = sysctl_sched_granularity * 8;
 	sysctl_sched_wakeup_granularity = sysctl_sched_granularity / 2;
 }