From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@suse.de>, Len Brown <lenb@kernel.org>,
x86@kernel.org, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Mel Gorman <mgorman@techsingularity.net>,
Matt Fleming <matt@codeblueprint.co.uk>,
Viresh Kumar <viresh.kumar@linaro.org>,
Juri Lelli <juri.lelli@redhat.com>, Paul Turner <pjt@google.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Quentin Perret <qperret@qperret.net>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Doug Smythies <dsmythies@telus.net>
Subject: Re: [PATCH v2 2/2] cpufreq: intel_pstate: Conditional frequency invariant accounting
Date: Thu, 03 Oct 2019 20:31:30 -0700 [thread overview]
Message-ID: <5d6d601d2647644238fc51621407061e1c29320d.camel@linux.intel.com> (raw)
In-Reply-To: <13106850.QMtCbivBLn@kreacher>
On Thu, 2019-10-03 at 20:05 +0200, Rafael J. Wysocki wrote:
> On Wednesday, October 2, 2019 2:29:26 PM CEST Giovanni Gherdovich
> wrote:
> > From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> >
> > intel_pstate has two operating modes: active and passive. In
> > "active"
> > mode, the in-built scaling governor is used and in "passive" mode,
> > the driver can be used with any governor like "schedutil". In
> > "active"
> > mode the utilization values from schedutil is not used and there is
> > a requirement from high performance computing use cases, not to
> > readas well
> > any APERF/MPERF MSRs.
>
> Well, this isn't quite convincing.
>
> In particular, I don't see why the "don't read APERF/MPERF MSRs"
> argument
> applies *only* to intel_pstate in the "active" mode. What about
> intel_pstate
> in the "passive" mode combined with the "performance" governor? Or
> any other
> governor different from "schedutil" for that matter?
>
> And what about acpi_cpufreq combined with any governor different from
> "schedutil"?
>
> Scale invariance is not really needed in all of those cases right now
> AFAICS,
> or is it?
Correct. This is just part of the patch to disable in active mode
(particularly in HWP and performance mode).
But this patch is 2 years old. The folks who wanted this, disable
intel-pstate and use userspace governor with acpi-cpufreq. So may be
better to address those cases too.
>
> So is the real concern that intel_pstate in the "active" mode reads
> the MPERF
> and APERF MSRs by itself and that kind of duplicates what the scale
> invariance
> code does and is redundant etc?
It is redundant in non-HWP mode. In HWP and performance (active mode)
we don't use atleast at this time.
Thanks
Srinivas
next prev parent reply other threads:[~2019-10-04 3:31 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-02 12:29 [PATCH v2 0/2] Add support for frequency invariance for (some) x86 Giovanni Gherdovich
2019-10-02 12:29 ` [PATCH v2 1/2] x86,sched: Add support for frequency invariance Giovanni Gherdovich
2019-10-02 15:23 ` kbuild test robot
2019-10-02 15:49 ` Giovanni Gherdovich
2019-10-02 16:43 ` kbuild test robot
2019-10-02 18:27 ` Peter Zijlstra
2019-10-03 10:27 ` Rafael J. Wysocki
2019-10-03 12:15 ` Peter Zijlstra
2019-10-03 17:36 ` Srinivas Pandruvada
2019-10-03 17:53 ` Rafael J. Wysocki
2019-10-04 11:48 ` Peter Zijlstra
2019-10-08 7:48 ` Giovanni Gherdovich
2019-10-08 9:32 ` Rafael J. Wysocki
2019-10-02 12:29 ` [PATCH v2 2/2] cpufreq: intel_pstate: Conditional frequency invariant accounting Giovanni Gherdovich
2019-10-03 18:05 ` Rafael J. Wysocki
2019-10-04 3:31 ` Srinivas Pandruvada [this message]
2019-10-04 8:08 ` Rafael J. Wysocki
2019-10-04 8:29 ` Giovanni Gherdovich
2019-10-04 8:28 ` Vincent Guittot
2019-10-04 8:33 ` Rafael J. Wysocki
2019-10-04 8:29 ` Rafael J. Wysocki
2019-10-04 8:57 ` Giovanni Gherdovich
2019-10-04 9:17 ` Rafael J. Wysocki
2019-10-04 15:17 ` Srinivas Pandruvada
2019-10-07 8:33 ` Giovanni Gherdovich
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