linux-kernel - Re: [PATCH 4/4] cpufreq: intel_pstate: enable boost for Skylake Xeon

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Message-ID: <41b51613acbdaf59294f436af057753978908470.camel@linux.intel.com>
Date:   Tue, 31 Jul 2018 12:07:08 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Eero Tamminen <eero.t.tamminen@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Francisco Jerez <currojerez@...eup.net>, lenb@...nel.org,
        rjw@...ysocki.net, ggherdovich@...e.cz, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        viresh.kumar@...aro.org, Chris Wilson <chris@...is-wilson.co.uk>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
Subject: Re: [PATCH 4/4] cpufreq: intel_pstate: enable boost for Skylake Xeon

On Tue, 2018-07-31 at 17:04 +0200, Peter Zijlstra wrote:
> 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):
We also have that for using space programs (E.g. KBL-G).

Thanks,
Srinivas

> 
>   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.