linux-kernel - Re: [patch v6 13/21] sched: using avg

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Date:	Wed, 03 Apr 2013 16:10:30 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v6 13/21] sched: using avg_idle to detect bursty wakeup

On 04/03/2013 01:08 PM, Namhyung Kim wrote:
>> > -	for_each_cpu(i, sched_group_cpus(group))
>> > -		sgs->group_util += max_rq_util(i);
>> > +	for_each_cpu(i, sched_group_cpus(group)) {
>> > +		struct rq *rq = cpu_rq(i);
>> > +
>> > +		if (burst && rq->nr_running > 1)
>> > +			/* use nr_running as instant utilization */
>> > +			sgs->group_util += rq->nr_running;
> I guess multiplying FULL_UTIL to rq->nr_running here will remove
> special-casing the burst in is_sd_full().  Also moving this logic to
> max_rq_util() looks better IMHO.
> 
> 

Thanks Namhyung! patch updated.

>From b6384f4e3294e19103f706195a95265faf1ea7ef Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@...el.com>
Date: Mon, 25 Mar 2013 16:07:39 +0800
Subject: [PATCH 12/21] sched: using avg_idle to detect bursty wakeup

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@...el.com>
---
 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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