linux-kernel - Re: [PATCH v2 1/7] cpufreq: move invariance setter calls in cpufreq core

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Message-ID: <CAJZ5v0gOJXtpF4iy2v+Jbv9y9QZsAtEREMQwWv0u7Zks0Fvp1A@mail.gmail.com>
Date:   Mon, 3 Aug 2020 15:46:59 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Will Deacon <will@...nel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH v2 1/7] cpufreq: move invariance setter calls in cpufreq core

On Mon, Aug 3, 2020 at 3:26 PM Ionela Voinescu <ionela.voinescu@....com> wrote:
>
> Hi guys,
>
> On Thursday 30 Jul 2020 at 09:11:28 (+0530), Viresh Kumar wrote:
> > On 27-07-20, 15:48, Rafael J. Wysocki wrote:
> > > On Wed, Jul 22, 2020 at 11:38 AM Ionela Voinescu
> > > <ionela.voinescu@....com> wrote:
> > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > > > index 036f4cc42ede..bac4101546db 100644
> > > > --- a/drivers/cpufreq/cpufreq.c
> > > > +++ b/drivers/cpufreq/cpufreq.c
> > > > @@ -2058,9 +2058,16 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier);
> > > >  unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
> > > >                                         unsigned int target_freq)
> > > >  {
> > > > +       unsigned int freq;
> > > > +
> > > >         target_freq = clamp_val(target_freq, policy->min, policy->max);
> > > > +       freq = cpufreq_driver->fast_switch(policy, target_freq);
> > > > +
> > > > +       if (freq)
> > > > +               arch_set_freq_scale(policy->related_cpus, freq,
> > > > +                                   policy->cpuinfo.max_freq);
> > >
> > > Why can't arch_set_freq_scale() handle freq == 0?
> >
>
> Sorry, I seem to have missed this question the first time around.
>
> arch_set_freq_scale() could handle freq == 0, but given that freq == 0
> is signaling an error here, I do believe this check is well placed, to
> prevent a useless call to arch_set_freq_scale(). Also [1]:

So let me rephrase:

Doesn't this check add overhead in the empty arch_set_freq_scale() case?