linux-kernel - Re: [PATCH 04/14] sched: pack the idle load balance

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Date:	Fri, 26 Apr 2013 14:49:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, mingo@...nel.org,
	linux@....linux.org.uk, pjt@...gle.com, santosh.shilimkar@...com,
	Morten.Rasmussen@....com, chander.kashyap@...aro.org,
	cmetcalf@...era.com, tony.luck@...el.com, alex.shi@...el.com,
	preeti@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	tglx@...utronix.de, len.brown@...el.com, arjan@...ux.intel.com,
	amit.kucheria@...aro.org, corbet@....net, l.majewski@...sung.com
Subject: Re: [PATCH 04/14] sched: pack the idle load balance

On Thu, Apr 25, 2013 at 07:23:20PM +0200, Vincent Guittot wrote:
> Look for an idle CPU close to the pack buddy CPU whenever possible.
> The goal is to prevent the wake up of a CPU which doesn't share the power
> domain of the pack buddy CPU.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> Reviewed-by: Morten Rasmussen <morten.rasmussen@....com>
> ---
>  kernel/sched/fair.c |   19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6adc57c..a985c98 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5469,7 +5469,26 @@ static struct {
>  
>  static inline int find_new_ilb(int call_cpu)
>  {
> +	struct sched_domain *sd;
>  	int ilb = cpumask_first(nohz.idle_cpus_mask);
> +	int buddy = per_cpu(sd_pack_buddy, call_cpu);
> +
> +	/*
> +	 * If we have a pack buddy CPU, we try to run load balance on a CPU
> +	 * that is close to the buddy.
> +	 */
> +	if (buddy != -1) {
> +		for_each_domain(buddy, sd) {
> +			if (sd->flags & SD_SHARE_CPUPOWER)
> +				continue;
> +
> +			ilb = cpumask_first_and(sched_domain_span(sd),
> +					nohz.idle_cpus_mask);
> +
> +			if (ilb < nr_cpu_ids)
> +				break;
> +		}
> +	}
>  
>  	if (ilb < nr_cpu_ids && idle_cpu(ilb))
>  		return ilb;

Ha! and here you hope people won't put multiple big-little clusters in a single
machine? :-)



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