Re: [PATCH v4 1/2] sched/fair: Check a task has a fitting cpu when updating misfit

Qais Yousef
2024-02-20T16:07:40Z

On 02/06/24 18:17, Dietmar Eggemann wrote:
> On 06/02/2024 16:06, Qais Yousef wrote:
> > On 02/05/24 20:49, Dietmar Eggemann wrote:
> >> On 26/01/2024 02:46, Qais Yousef wrote:
> >>> On 01/25/24 18:40, Vincent Guittot wrote:
> >>>> On Wed, 24 Jan 2024 at 23:30, Qais Yousef <qyousef@layalina.io> wrote:
> >>>>>
> >>>>> On 01/23/24 09:26, Vincent Guittot wrote:
> >>>>>> On Fri, 5 Jan 2024 at 23:20, Qais Yousef <qyousef@layalina.io> wrote:
> >>>>>>>
> >>>>>>> From: Qais Yousef <qais.yousef@arm.com>
>
> [...]
>
> >>> It seems we flatten topologies but not sched domains. I see all cpus shown as
> >>> core_siblings. The DT for apple silicon sets clusters in the cpu-map - which
> >>> seems the flatten topology stuff detect LLC correctly but still keeps the
> >>> sched-domains not flattened. Is this a bug? I thought we will end up with one
> >>> sched domain still.
> >>
> >> IMHO, if you have a cpu_map entry with > 1 cluster in your dtb, you end
> >> up with MC and PKG (former DIE) Sched Domain (SD) level. And misfit load
> >
> > Hmm, okay. I thought the detection of topology where we know the LLC is shared
> > will cause the sched domains to collapse too.
> >
> >> balance takes potentially longer on PKG than to MC.
> >
> > Why potentially longer? We iterate through the domains the CPU belong to. If
> > the first iteration (at MC) pulled something, then once we go to PKG then we're
> > less likely to pull again?
>
> There are a couple of mechanisms in place to let load-balance on higher
> sd levels happen less frequently, eg:
>
> load_balance() -> should_we_balance() + continue_balancing
>
> interval = get_sd_balance_interval(sd, busy) in rebalance_domains()
>
> rq->avg_idle versus sd->max_newidle_lb_cost

Okay thanks. That last one I missed.

>
> > Anyway. I think I am hitting a bug here. The behavior doesn't look right to me
> > given the delays I'm seeing and the fact we do the ilb but for some reason fail
> > to pull
>
> [...]
>