linux-kernel - Re: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting

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Message-ID: <20180517161649.GX12217@hirez.programming.kicks-ass.net>
Date:   Thu, 17 May 2018 18:16:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     Juri Lelli <juri.lelli@...hat.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...e.de, lenb@...nel.org, rjw@...ysocki.net,
        mgorman@...hsingularity.net, x86@...nel.org,
        linux-pm@...r.kernel.org, viresh.kumar@...aro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional
 frequency invariant accounting

On Thu, May 17, 2018 at 08:41:32AM -0700, Srinivas Pandruvada wrote:
> One more point to note. Even if we calculate some utilization based on
> the freq-invariant and arrive at a P-state, we will not be able to
> control any P-state in turbo region (not even as a cap) on several
> Intel processors using PERF_CTL MSRs.

Right, but don't we need to set the PERF_CTL to max P in order to access
the turbo bins? So we still need to compute a P state, but as soon as we
reach max P, we're done.

And its not as if setting anything below max P is a firm setting either
anyway, its hints all the way down.