linux-kernel - Re: [PATCH 1/2] x86,sched: Add support for frequency invariance

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Date:   Wed, 02 Oct 2019 14:26:44 +0200
From:   Giovanni Gherdovich <ggherdovich@...e.cz>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     srinivas.pandruvada@...ux.intel.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...e.de, lenb@...nel.org, rjw@...ysocki.net,
        x86@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mgorman@...hsingularity.net,
        matt@...eblueprint.co.uk, viresh.kumar@...aro.org,
        juri.lelli@...hat.com, pjt@...gle.com, vincent.guittot@...aro.org,
        qperret@...rret.net, dietmar.eggemann@....com
Subject: Re: [PATCH 1/2] x86,sched: Add support for frequency invariance

On Tue, 2019-09-24 at 18:04 +0200, Peter Zijlstra wrote:
> On Mon, Sep 09, 2019 at 04:42:15AM +0200, Giovanni Gherdovich wrote:
> 
> > +static void intel_set_cpu_max_freq(void)
> > +{
> > +	/*
> > +	 * TODO: add support for:
> > +	 *
> > +	 * - Xeon Phi (KNM, KNL)
> > +	 * - Xeon Gold/Platinum, Atom Goldmont/Goldmont Plus
> > +	 * - Atom Silvermont
> 
> ISTR I had code for Atom.. what happened with that?

I'm being overly zealous and I wanted to get a Silvermont machine to test that
code before sending.

The reason is that your code uses MSR_ATOM_CORE_RATIOS and
MSR_ATOM_CORE_TURBO_RATIOS which are not documented in the SDM. I wanted to
make sure those have the expected content on at least one machine before using
them in my code. I have no doubt you, Srinivas and Len (who uses them in
turbostat) have already checked but you know, more eyeballs.

I've talked to Len and Srinivas at LPC, they agreed that those two MSR may not
have made it to the SDM but said the turbostat source code is the reference in
this case.

Giovanni