sched: Add sysctl_sched_shares_window

Introduce a new sysctl for the shares window and disambiguate it from
sched_time_avg.

A 10ms window appears to be a good compromise between accuracy and performance.
Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234938.112173964@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/sched.h

@@ -1900,6 +1900,7 @@ extern unsigned int sysctl_sched_migration_cost;
 extern unsigned int sysctl_sched_nr_migrate;
 extern unsigned int sysctl_sched_time_avg;
 extern unsigned int sysctl_timer_migration;
+extern unsigned int sysctl_sched_shares_window;
 
 int sched_proc_update_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *length,

kernel/sched_fair.c

@@ -89,6 +89,13 @@ unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;
 
 const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
 
+/*
+ * The exponential sliding  window over which load is averaged for shares
+ * distribution.
+ * (default: 10msec)
+ */
+unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;
+
 static const struct sched_class fair_sched_class;
 
 /**************************************************************
@@ -688,7 +695,7 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 #if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
 static void update_cfs_load(struct cfs_rq *cfs_rq)
 {
-	u64 period = sched_avg_period();
+	u64 period = sysctl_sched_shares_window;
 	u64 now, delta;
 	unsigned long load = cfs_rq->load.weight;
 

kernel/sysctl.c

@@ -332,6 +332,13 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "sched_shares_window",
+		.data		= &sysctl_sched_shares_window,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{
 		.procname	= "timer_migration",
 		.data		= &sysctl_timer_migration,