[PATCH v5 1/3] sched: Reduce overestimating rq->avg_idle

[Jason Low <jason.low2@hp.com>]

When updating avg_idle, if the delta exceeds some max value, then avg_idle
gets set to the max, regardless of what the previous avg was. This can cause
avg_idle to often be overestimated.

This patch modifies the way we update avg_idle by always updating it with the
function call to update_avg() first. Then, if avg_idle exceeds the max, we set
it to the max.

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 kernel/sched/core.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 725aa06..25b0f79 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1347,10 +1347,11 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 		u64 delta = rq_clock(rq) - rq->idle_stamp;
 		u64 max = 2*sysctl_sched_migration_cost;
 
-		if (delta > max)
+		update_avg(&rq->avg_idle, delta);
+
+		if (rq->avg_idle > max)
 			rq->avg_idle = max;
-		else
-			update_avg(&rq->avg_idle, delta);
+
 		rq->idle_stamp = 0;
 	}
 #endif
-- 
1.7.1