[RFC PATCH v3 5/6] sched: pack the idle load balance

[Peter Zijlstra]

On Fri, 2013-03-22 at 13:25 +0100, 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 at linaro.org>
> Reviewed-by: Morten Rasmussen <morten.rasmussen at arm.com>
> ---
>  kernel/sched/fair.c |   18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b636199..52a7736 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5455,7 +5455,25 @@ 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;
> +               }

/me hands you a fresh bucket of curlies, no reason to skimp on them.

But ha! here's your NO_HZ link.. but does the above DTRT and ensure
that the ILB is a little core when possible?