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SubjectRe: [PATCH v10 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
On Thu, Aug 24, 2017 at 09:55:14AM -0400, Steven Rostedt wrote:
> On Thu, 24 Aug 2017 10:06:03 +0900
> Byungchul Park <byungchul.park@lge.com> wrote:
>
> > Hello Steven,
> >
> > Can I keep your reviewed-by with comments modified?
>
> Yes, but I have one nit.
>
>
> > @@ -1668,9 +1691,35 @@ static int find_lowest_rq(struct task_struct *task)
> > return this_cpu;
> > }
> >
> > - best_cpu = cpumask_first_and(lowest_mask,
> > - sched_domain_span(sd));
> > + /*
> > + * If a cpu being in lowest_mask & current sd &
> > + * ~prefer sd is valid, that becomes our choice.
>
> I can't parse the above sentence.

I might have simplified the comment too much.

~prefer means we want to exclude the domain span having SD_PREFER_SIBLING,
since they should be considered as fallback candidates.

W/o ~prefer, a cpu in the domain might be chosen when we consider higher
domain than the domain having SD_PREFER_SIBLING, as the best cpu, not
fallback.

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