linux-kernel - Re: [PATCH V2] sched: Improve load balancing in the presence of idle CPUs

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Date:	Thu, 26 Mar 2015 10:03:20 -0700
From:	Jason Low <jason.low2@...com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	peterz@...radead.org, mingo@...nel.org, riel@...hat.com,
	daniel.lezcano@...aro.org, vincent.guittot@...aro.org,
	srikar@...ux.vnet.ibm.com, pjt@...gle.com,
	benh@...nel.crashing.org, efault@....de,
	linux-kernel@...r.kernel.org, iamjoonsoo.kim@....com,
	svaidy@...ux.vnet.ibm.com, tim.c.chen@...ux.intel.com,
	morten.rasmussen@....com, jason.low2@...com
Subject: Re: [PATCH V2] sched: Improve load balancing in the presence of
 idle CPUs

On Thu, 2015-03-26 at 18:32 +0530, Preeti U Murthy wrote:
>  kernel/sched/fair.c |    8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bcfe320..8b6d0d5 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7660,14 +7660,16 @@ static void run_rebalance_domains(struct softirq_action *h)
>  	enum cpu_idle_type idle = this_rq->idle_balance ?
>  						CPU_IDLE : CPU_NOT_IDLE;
>  
> -	rebalance_domains(this_rq, idle);
> -
>  	/*
>  	 * If this cpu has a pending nohz_balance_kick, then do the
>  	 * balancing on behalf of the other idle cpus whose ticks are
> -	 * stopped.
> +	 * stopped. Do nohz_idle_balance *before* rebalance_domains to
> +	 * give the idle cpus a chance to load balance. Else we may
> +	 * load balance only within the local sched_domain hierarchy
> +	 * and abort nohz_idle_balance altogether if we pull some load.
>  	 */
>  	nohz_idle_balance(this_rq, idle);
> +	rebalance_domains(this_rq, idle);

Reviewed-by: Jason Low <jason.low2@...com>

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