sched: fix stale value in average load per task

Impact: fix load balancer load average calculation accuracy

cpu_avg_load_per_task() returns a stale value when nr_running is 0.
It returns an older stale (caculated when nr_running was non zero) value.

This patch returns and sets rq->avg_load_per_task to zero when nr_running
is 0.

Compile and boot tested on a x86_64 box.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 50a21f964679ec42eee299cab7f7f86edc26a408..3bafbe350f4f305b545abdbbcba179a22da6ec4f 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1456,6 +1456,8 @@ static unsigned long cpu_avg_load_per_task(int cpu)
 
        if (rq->nr_running)
                rq->avg_load_per_task = rq->load.weight / rq->nr_running;
+       else
+               rq->avg_load_per_task = 0;
 
        return rq->avg_load_per_task;
 }