Re: [PATCH 04/16] sched/fair: Optimize find_idlest_cpu() when there is no choice

Peter Zijlstra
2016-06-01T19:59:27Z

On Mon, May 23, 2016 at 11:58:46AM +0100, Morten Rasmussen wrote:
> In the current find_idlest_group()/find_idlest_cpu() search we end up
> calling find_idlest_cpu() in a sched_group containing only one cpu in
> the end. Checking idle-states becomes pointless when there is no
> alternative, so bail out instead.
>
> cc: Ingo Molnar <mingo@redhat.com>
> cc: Peter Zijlstra <peterz@infradead.org>
>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
> ---
> kernel/sched/fair.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0fe3020..564215d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5155,6 +5155,11 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
> int shallowest_idle_cpu = -1;
> int i;
>
> + /* Check if we have any choice */
> + if (group->group_weight == 1) {
> + return cpumask_first(sched_group_cpus(group));
> + }

superfluous brackets, also isn't @this_cpu supposed to be part of the
sched_group_cpu(group) mask?