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

[Peter Zijlstra <peterz@infradead.org>]

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@linaro.org>
> Reviewed-by: Morten Rasmussen <morten.rasmussen@arm.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? :-)