From: Giovanni Gherdovich <email@example.com>
To: Srinivas Pandruvada <firstname.lastname@example.org>,
"Rafael J. Wysocki" <email@example.com>
Cc: Thomas Gleixner <firstname.lastname@example.org>,
Ingo Molnar <email@example.com>,
Peter Zijlstra <firstname.lastname@example.org>,
Borislav Petkov <email@example.com>, Len Brown <firstname.lastname@example.org>,
Mel Gorman <email@example.com>,
Matt Fleming <firstname.lastname@example.org>,
Viresh Kumar <email@example.com>,
Juri Lelli <firstname.lastname@example.org>, Paul Turner <email@example.com>,
Vincent Guittot <firstname.lastname@example.org>,
Quentin Perret <email@example.com>,
Dietmar Eggemann <firstname.lastname@example.org>,
Doug Smythies <email@example.com>
Subject: Re: [PATCH v2 2/2] cpufreq: intel_pstate: Conditional frequency invariant accounting
Date: Fri, 04 Oct 2019 10:29:46 +0200 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On Thu, 2019-10-03 at 20:31 -0700, Srinivas Pandruvada wrote:
> 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 <email@example.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.
I disagree with "scale invariance is needed only by the schedutil governor";
the two other users are the CPU's estimated utilization in the wakeup path,
via cpu_util_without(), as well as the load-balance path, via cpu_util() which
is used by update_sg_lb_stats().
Also remember that scale invariance is applied to both PELT signals util_avg
and load_avg; schedutil uses the former but not the latter.
I understand Srinivas patch to disable MSR accesses during the tick as a
band-aid solution to address a specific use case he cares about, but I don't
think that extending this approach to any non-schedutil governor is a good
idea -- you'd be killing load balancing in the process.
next prev parent reply other threads:[~2019-10-04 8:24 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
2019-10-04 8:08 ` Rafael J. Wysocki
2019-10-04 8:29 ` Giovanni Gherdovich [this message]
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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