Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 17 Apr 2020 14:19:45 +0200
From:   Juri Lelli <juri.lelli@redhat.com>
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Valentin Schneider <valentin.schneider@arm.com>,
        luca abeni <luca.abeni@santannapisa.it>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Wei Wang <wvw@google.com>, Quentin Perret <qperret@google.com>,
        Alessio Balsini <balsini@google.com>,
        Pavan Kondeti <pkondeti@codeaurora.org>,
        Patrick Bellasi <patrick.bellasi@matbug.net>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Qais Yousef <qais.yousef@arm.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] sched/deadline: Improve admission control for
 asymmetric CPU capacities
Message-ID: <20200417121945.GM9767@localhost.localdomain>
References: <20200408095012.3819-1-dietmar.eggemann@arm.com>
 <20200408095012.3819-3-dietmar.eggemann@arm.com>
 <jhjeesyw96u.mognet@arm.com>
 <20200408153032.447e098d@nowhere>
 <jhjblo2vx60.mognet@arm.com>
 <31620965-e1e7-6854-ad46-8192ee4b41af@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <31620965-e1e7-6854-ad46-8192ee4b41af@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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