linux-kernel - Re: [PATCH 2/4] sched/deadline: Improve admission control for asymmetric CPU capacities

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Date:   Tue, 14 Apr 2020 15:29:00 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        luca abeni <luca.abeni@...tannapisa.it>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Wei Wang <wvw@...gle.com>, Quentin Perret <qperret@...gle.com>,
        Alessio Balsini <balsini@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Morten Rasmussen <morten.rasmussen@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] sched/deadline: Improve admission control for asymmetric CPU capacities


On 14/04/20 12:40, Qais Yousef wrote:
>
> I haven't followed this discussion closely, so I could be missing something
> here.
>
> In sched_cpu_dying() we call set_rq_offline() which clears the cpu in
> rq->rd->online.
>
> So the way I read the code
>
>       rd->online = cpumask_and(rd->span, cpu_active_mask)
>
> But I could have easily missed some detail.
>

sched_cpu_dying() is wayyyy below sched_cpu_deactivate(). This doesn't help
at all for the dl_cpu_busy() check in sched_cpu_deactivate().

> Regardless, it seems to me that DL is working around something not right in the
> definition of rd->span or using the wrong variable.
>

What DL is doing now is fine, it only needs to be aligned with the active
mask (which it is). We're making things a bit trickier by adding capacity
values into the mix.

> My 2p :-). I have to go back and read the discussion in more detail.
>
> Thanks