sched/rt: Add a tuning knob to allow changing SCHED_RR timeslice

Add a /proc/sys/kernel scheduler knob named
sched_rr_timeslice_ms that allows global changing of the
SCHED_RR timeslice value. User visable value is in milliseconds
but is stored as jiffies.  Setting to 0 (zero) resets to the
default (currently 100ms).

Signed-off-by: Clark Williams <williams@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20130207094704.13751796@riff.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/sysctl.h

@@ -73,6 +73,13 @@ static inline unsigned int get_sysctl_timer_migration(void)
 	return 1;
 }
 #endif
+
+/*
+ *  control realtime throttling:
+ *
+ *  /proc/sys/kernel/sched_rt_period_us
+ *  /proc/sys/kernel/sched_rt_runtime_us
+ */
 extern unsigned int sysctl_sched_rt_period;
 extern int sysctl_sched_rt_runtime;
 
@@ -90,7 +97,13 @@ extern unsigned int sysctl_sched_autogroup_enabled;
  */
 #define RR_TIMESLICE		(100 * HZ / 1000)
 
-int sched_rt_handler(struct ctl_table *table, int write,
+extern int sched_rr_timeslice;
+
+extern int sched_rr_handler(struct ctl_table *table, int write,
+		void __user *buffer, size_t *lenp,
+		loff_t *ppos);
+
+extern int sched_rt_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos);