Re: [PATCH] sched/fair: consider sched-idle CPU when selecting idle core

[Jiang Biao]

On Fri, 24 Jul 2020 at 15:24, Vincent Guittot
<vincent.guittot@xxxxxxxxxx> wrote:
>
> On Fri, 24 Jul 2020 at 01:39, Jiang Biao <humjb_1983@xxxxxxx> wrote:
> >
> > From: Jiang Biao <benbjiang@xxxxxxxxxxx>
> >
> > Sched-idle CPU has been considered in select_idle_cpu and
> > select_idle_smt, it also needs to be considered in select_idle_core to
> > be consistent and keep the same *idle* policy.
>
> In the case of select_idle_core, we are looking for a core that is
> fully idle but if one CPU of the core is running a sched_idle task,
> the core will not be idle and we might end up having  the wakeup task
> on a CPU and a sched_idle task on another CPU of the core which is not
> what we want
Got it. sched_idle task may interfere its sibling, which brings me
another question,
If there's a core with smt1 running sched_idle task and smt2 idle,
selecting smt1
rather than smt2 should be more helpful for wakee task, because wakee task
could suppress the sched_idle task without neighbour interfering.
And there seems to be no consideration about that currently.
Is it worth improving that?

Thanks a lot.

Regards,
Jiang