[PATCH 12/21] sched: using avg_idle to detect bursty wakeup

[Alex Shi]

Sleeping task has no utiliation, when they were bursty waked up, the
zero utilization make scheduler out of balance, like aim7 benchmark.

rq->avg_idle is 'to used to accommodate bursty loads in a dirt simple
dirt cheap manner' -- Mike Galbraith.

With this cheap and smart bursty indicator, we can find the wake up
burst, and use nr_running as instant utilization in this scenario.

For other scenarios, we still use the precise CPU utilization to
judage if a domain is eligible for power scheduling.

Thanks for Mike Galbraith's idea!
Thanks for Namhyung's suggestion to compact the burst into
max_rq_util()!

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f610313..a729939 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3363,6 +3363,10 @@ static unsigned int max_rq_util(int cpu)
 	unsigned int cfs_util;
 	unsigned int nr_running;
 
+	/* use nr_running as instant utilization for burst cpu */
+	if (cpu_rq(cpu)->avg_idle < sysctl_sched_burst_threshold)
+		return rq->nr_running * FULL_UTIL;
+
 	/* yield cfs utilization to rt's, if total utilization > 100% */
 	cfs_util = min(rq->util, (unsigned int)(FULL_UTIL - rt_util));
 
-- 
1.7.12


-- 
Thanks Alex
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