sched: fix stale value in average load per task

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 <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>