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Date:   Tue, 31 Jul 2018 17:04:38 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc:     Eero Tamminen <eero.t.tamminen@intel.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Francisco Jerez <currojerez@riseup.net>, lenb@kernel.org,
        rjw@rjwysocki.net, ggherdovich@suse.cz, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
        viresh.kumar@linaro.org, Chris Wilson <chris@chris-wilson.co.uk>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Subject: Re: [PATCH 4/4] cpufreq: intel_pstate: enable boost for Skylake Xeon
Message-ID: <20180731150438.GE2458@hirez.programming.kicks-ass.net>
References: <20180605214242.62156-1-srinivas.pandruvada@linux.intel.com>
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 <e7388bf4-deb1-34b6-97d7-89ced8e78ef1@intel.com>
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On Mon, Jul 30, 2018 at 07:06:21AM -0700, Srinivas Pandruvada wrote:
> On Mon, 2018-07-30 at 14:16 +0300, Eero Tamminen wrote:
> > Questions:
> > 
> > * Does currently kernel CPU freq management have any idea which IO
> >    devices share TDP with the CPU cores?

> No. The requests we do to hardware is just indication only (HW can
> ignore it). The HW has a bias register to adjust and distribute power
> among users.
> We can have several other active device on servers beside CPU which
> when runs need extra power. So the HW arbitrates power.

That's not entirely accurate AFAIK. "No" is accurate for Intel, but the
ARM people have their IPA thing (not a beer):

  https://developer.arm.com/open-source/intelligent-power-allocation

  drivers/thermal/power_allocator.c

which IIUC interacts with their cpufreq driver to disallow certain OPP
states.

And note that I discourage intel_pstate active mode.