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Message-ID: <20200417121945.GM9767@localhost.localdomain>
Date: Fri, 17 Apr 2020 14:19:45 +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 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?
> struct cpumask *cpus = this_cpu_cpumask_var_ptr(dl_bw_mask);
> ...
> cpumask_and(cpus, rd->span, cpu_active_mask);
>
> return cpumask_weight(cpus);
> }
>
> and
>
> dl_bw_capacity(int i) {
>
> struct cpumask *cpus = this_cpu_cpumask_var_ptr(dl_bw_mask);
> ...
> cpumask_and(cpus, rd->span, cpu_active_mask);
> if (cpumask_equal(cpus, rd->span))
> return rd->sum_cpu_capacity;
What if capacities change between invocations (with the same span)?
Can that happen?
>
> for_each_cpu(i, cpus)
> cap += capacity_orig_of(i);
>
> return cap;
> }
>
> So only in cases in which rd->span and cpu_active_mask differ we would
> have to sum up again.
Thanks,
Juri
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