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

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Date:   Fri, 17 Apr 2020 17:47:38 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        luca abeni <luca.abeni@...tannapisa.it>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        Qais Yousef <qais.yousef@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] sched/deadline: Improve admission control for
 asymmetric CPU capacities

On 17/04/20 17:08, Juri Lelli wrote:
> On 17/04/20 16:55, Dietmar Eggemann wrote:
> > On 17.04.20 14:19, Juri Lelli wrote:
> > > On 09/04/20 19:29, Dietmar Eggemann wrote:
> > 
> > [...]
> > 
> > >> Maybe we can do a hybrid. We have rd->span and rd->sum_cpu_capacity and
> > >> with the help of an extra per-cpu cpumask we could just
> > > 
> > > Hummm, I like the idea, but
> > > 
> > >> DEFINE_PER_CPU(cpumask_var_t, dl_bw_mask);
> > >>
> > >> dl_bw_cpus(int i) {
> > > 
> > > This works if calls are always local to the rd we are interested into
> > > (argument 'i' isn't used). Are we always doing that?
> > 
> > I thought so. The existing dl_bw_cpus(int i) implementation already
> > assumes this by using:
> > 
> >     struct root_domain *rd = cpu_rq(i)->rd;
> 
> Hummm, can't dl_task_can_attach() call it with a dest_cpu different from
> this_cpu?
> 
> Current implementation uses 'i' argument to get to the right root_domain
> (e.g., when moving tasks between execlusive set).
> 
> >     ...

Bah, forget that. If everything else stays the same (get rd using 'i')
this should work ok.