linux-kernel - Re: [patch v3 0/8] sched: use runnable avg in load balance

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Date:	Wed, 03 Apr 2013 14:22:12 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Alex Shi <alex.shi@...el.com>
CC:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, namhyung@...nel.org, efault@....de,
	morten.rasmussen@....com, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
	len.brown@...el.com, rafael.j.wysocki@...el.com, jkosina@...e.cz,
	clark.williams@...il.com, tony.luck@...el.com,
	keescook@...omium.org, mgorman@...e.de, riel@...hat.com
Subject: Re: [patch v3 0/8] sched: use runnable avg in load balance

On 04/03/2013 12:28 PM, Alex Shi wrote:
> On 04/03/2013 11:23 AM, Michael Wang wrote:
>> On 04/03/2013 10:56 AM, Alex Shi wrote:
>>> On 04/03/2013 10:46 AM, Michael Wang wrote:
[snip]
> 
> 
> From 4722a7567dccfb19aa5afbb49982ffb6d65e6ae5 Mon Sep 17 00:00:00 2001
> From: Alex Shi <alex.shi@...el.com>
> Date: Tue, 2 Apr 2013 10:27:45 +0800
> Subject: [PATCH] sched: use instant load for burst wake up
> 
> If many tasks sleep long time, their runnable load are zero. And if they
> are waked up bursty, too light runnable load causes big imbalance among
> CPU. So such benchmark, like aim9 drop 5~7%.
> 
> With this patch the losing is covered, and even is slight better.

A fast test show the improvement disappear and the regression back
again...after applied this one as the 8th patch, it doesn't works.

Regards,
Michael Wang

> 
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  kernel/sched/fair.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index dbaa8ca..25ac437 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3103,12 +3103,24 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
>  	unsigned long weight;
>  	int balanced;
>  	int runnable_avg;
> +	int burst = 0;
> 
>  	idx	  = sd->wake_idx;
>  	this_cpu  = smp_processor_id();
>  	prev_cpu  = task_cpu(p);
> -	load	  = source_load(prev_cpu, idx);
> -	this_load = target_load(this_cpu, idx);
> +
> +	if (cpu_rq(this_cpu)->avg_idle < sysctl_sched_migration_cost ||
> +		cpu_rq(prev_cpu)->avg_idle < sysctl_sched_migration_cost)
> +		burst= 1;
> +
> +	/* use instant load for bursty waking up */
> +	if (!burst) {
> +		load = source_load(prev_cpu, idx);
> +		this_load = target_load(this_cpu, idx);
> +	} else {
> +		load = cpu_rq(prev_cpu)->load.weight;
> +		this_load = cpu_rq(this_cpu)->load.weight;
> +	}
> 
>  	/*
>  	 * If sync wakeup then subtract the (maximum possible)
> 

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