linux-kernel - Re: [PATCH v2 3/3] cpufreq: intel_pstate: Update max frequency on global turbo changes

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Date:   Tue, 5 Mar 2019 12:55:47 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Chen Yu <yu.c.chen@...el.com>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>
Subject: Re: [PATCH v2 3/3] cpufreq: intel_pstate: Update max frequency on
 global turbo changes

On Tue, Mar 5, 2019 at 12:43 PM Quentin Perret <quentin.perret@....com> wrote:
>
> On Tuesday 05 Mar 2019 at 11:42:06 (+0100), Rafael J. Wysocki wrote:
> > +static void intel_pstate_update_max_freq(unsigned int cpu)
> > +{
> > +     struct cpufreq_policy *policy = cpufreq_cpu_acquire(cpu);
> > +     struct cpufreq_policy new_policy;
> > +     struct cpudata *cpudata;
> > +
> > +     if (!policy)
> > +             return;
> > +
> > +     cpudata = all_cpu_data[cpu];
> > +     policy->cpuinfo.max_freq = global.turbo_disabled_mf ?
> > +                     cpudata->pstate.max_freq : cpudata->pstate.turbo_freq;
>
> I'm not too familiar with how the Intel turbo stuff so bear with me but
> is this 'pstate.turbo_freq' constant ?

Yes, it is.

> Why not just write it unconditionally into cpuinfo.max_freq ? It's not
> guaranteed to always be reachable anyways no ? So maybe that's OK to always
> report that one regardless of the boost availability ?

So the concern is that on some systems turbo is disabled permanently
by the platform FW and it doesn't make sense to even take
pstate.turbo_freq into consideration then.