linux-kernel - Re: [PATCH 2/8] cpufreq: move invariance setter calls in cpufreq core

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Message-ID: <20200702030149.stwqpozhrspjz7sp@vireshk-i7>
Date:   Thu, 2 Jul 2020 08:31:49 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Ionela Voinescu <ionela.voinescu@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Will Deacon <will@...nel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/8] cpufreq: move invariance setter calls in cpufreq core

On 01-07-20, 17:51, Rafael J. Wysocki wrote:
> On Wed, Jul 1, 2020 at 5:28 PM Ionela Voinescu <ionela.voinescu@....com> wrote:
> > On Wednesday 01 Jul 2020 at 16:16:19 (+0530), Viresh Kumar wrote:
> > > On 01-07-20, 10:07, Ionela Voinescu wrote:
> > > > setpolicy()
> > > > ===========
> > > > This callback does not have any designated way of informing what was the
> > > > end choice. But there are only two drivers using setpolicy(), and none
> > > > of them have current FIE support:
> > > >
> > > >   drivers/cpufreq/longrun.c:281:    .setpolicy      = longrun_set_policy,
> > > >   drivers/cpufreq/intel_pstate.c:2215:      .setpolicy      = intel_pstate_set_policy,
> > > >
> > > > The intel_pstate is known to use counter-driven frequency invariance.
> > >
> > > Same for acpi-cpufreq driver as well ?
> > >
> >
> > The acpi-cpufreq driver defines target_index() and fast_switch() so it
> > should go through the setting in cpufreq core. But x86 does not actually
> > define arch_set_freq_scale() so when called it won't do anything (won't
> > set any frequency scale factor), but rely on counters to set it through
> > the arch_scale_freq_tick().
> 
> Right.
> 
> So on x86 (Intel flavor of it at least), cpufreq has nothing to do
> with this regardless of what driver is in use.

-- 
viresh