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Subject: Re: [PATCH 1/4] sched/topology: Store root domain CPU capacity sum
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Luca Abeni <luca.abeni@santannapisa.it>,
        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>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Qais Yousef <qais.yousef@arm.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <20200408095012.3819-1-dietmar.eggemann@arm.com>
 <20200408095012.3819-2-dietmar.eggemann@arm.com>
 <CAKfTPtC4_+dTddLdoFMdzUvsXwWyi3bUOXcg9kstC8RzZS_a+A@mail.gmail.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <42cc3878-4c57-96ba-3ebd-1b4d4ef87fae@arm.com>
Date:   Wed, 8 Apr 2020 18:30:54 +0200
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On 08.04.20 14:29, Vincent Guittot wrote:
> On Wed, 8 Apr 2020 at 11:50, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:

[...]

>>  /**
>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
>> index 8344757bba6e..74b0c0fa4b1b 100644
>> --- a/kernel/sched/topology.c
>> +++ b/kernel/sched/topology.c
>> @@ -2052,12 +2052,17 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
>>         /* Attach the domains */
>>         rcu_read_lock();
>>         for_each_cpu(i, cpu_map) {
>> +               unsigned long cap = arch_scale_cpu_capacity(i);
> 
> Why do you replace the use of rq->cpu_capacity_orig by
> arch_scale_cpu_capacity(i) ?
> There is nothing about this change in the commit message

True. And I can change this back.

It seems though that the solution is not sufficient because of the
'rd->span &nsub cpu_active_mask' issue discussed under patch 2/4.

But this remind me of another question I have.

Currently we use arch_scale_cpu_capacity() more often (16 times) than
capacity_orig_of()/rq->cpu_capacity_orig .

What's hindering us to remove rq->cpu_capacity_orig and the code around
it and solely rely on arch_scale_cpu_capacity()? I mean the arch
implementation should be fast.