Re: [PATCH v2] sched/cpuset: distribute tasks within affinity masks

[Josh Don]

On Wed, Mar 11, 2020 at 7:05 AM Qais Yousef <qais.yousef@xxxxxxx> wrote:
>
> This actually helps me fix a similar problem I faced in RT [1]. If multiple RT
> tasks wakeup at the same time we get a 'thundering herd' issue where they all
> end up going to the same CPU, just to be pushed out again.
>
> Beside this will help fix another problem for RT tasks fitness, which is
> a manifestation of the problem above. If two tasks wake up at the same time and
> they happen to run on a little cpu (but request to run on a big one), one of
> them will end up being migrated because find_lowest_rq() will return the first
> cpu in the mask for both tasks.
>
> I tested the API (not the change in sched/core.c) and it looks good to me.

Nice, glad that the API already has another use case. Thanks for taking a look.

> nit: cpumask_first_and() is better here?

Yea, I would also prefer to use it, but the definition of
cpumask_first_and() follows this section, as it itself uses
cpumask_next_and().

> It might be a good idea to split the API from the user too.

Not sure what you mean by this, could you clarify?

On Tue, Mar 17, 2020 at 12:24 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> > Anyway, for the API.
> >
> > Reviewed-by: Qais Yousef <qais.yousef@xxxxxxx>
> > Tested-by: Qais Yousef <qais.yousef@xxxxxxx>
>
> Thanks guys!

Thanks Peter, any other comments or are you happy with merging this patch as-is?