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SubjectRe: [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
On Thu, Aug 17, 2017 at 09:51:34PM -0700, Joel Fernandes (Google) wrote:
> On Thu, Aug 17, 2017 at 6:25 PM, Byungchul Park <byungchul.park@lge.com> wrote:
> > On Mon, Aug 07, 2017 at 12:50:32PM +0900, Byungchul Park wrote:
> >> When cpudl_find() returns any among free_cpus, the cpu might not be
> >> closer than others, considering sched domain. For example:
> >>
> >> this_cpu: 15
> >> free_cpus: 0, 1,..., 14 (== later_mask)
> >> best_cpu: 0
> >>
> >> topology:
> >>
> >> 0 --+
> >> +--+
> >> 1 --+ |
> >> +-- ... --+
> >> 2 --+ | |
> >> +--+ |
> >> 3 --+ |
> >>
> >> ... ...
> >>
> >> 12 --+ |
> >> +--+ |
> >> 13 --+ | |
> >> +-- ... -+
> >> 14 --+ |
> >> +--+
> >> 15 --+
> >>
> >> In this case, it would be best to select 14 since it's a free cpu and
> >> closest to 15(this_cpu). However, currently the code select 0(best_cpu)
> >> even though that's just any among free_cpus. Fix it.
> >
> > Could you let me know your opinions about this?
>
> Patch looks good to me, I would also add a comment ontop of
> fallback_cpu (I think Steve mentioned similar thing at [1])
>
> /*
> * fallback is the closest CPU in the closest SD incase
> * all domains are PREFER_SIBLING
> */
> if (fallback_cpu == -1)
> fallback_cpu = best_cpu;
>
> And clarify this in the commit message.

Right. I will add it.

Thank you very much,
Byungchul

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