From: Srinivas Pandruvada <firstname.lastname@example.org>
To: Giovanni Gherdovich <email@example.com>,
firstname.lastname@example.org, email@example.com, firstname.lastname@example.org,
email@example.com, firstname.lastname@example.org, email@example.com
Cc: firstname.lastname@example.org, email@example.com,
Subject: Re: [PATCH 1/2] x86,sched: Add support for frequency invariance
Date: Thu, 19 Sep 2019 16:55:22 -0700 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On Tue, 2019-09-17 at 16:27 +0200, Giovanni Gherdovich wrote:
> Hello Srinivas,
> On Fri, 2019-09-13 at 15:52 -0700, Srinivas Pandruvada wrote:
> > On Mon, 2019-09-09 at 04:42 +0200, Giovanni Gherdovich wrote:
> > ...
> > > +
> > > +/*
> > > + * APERF/MPERF frequency ratio computation.
> > > + *
> > > + * The scheduler wants to do frequency invariant accounting and
> > > needs a <1
> > > + * ratio to account for the 'current' frequency, corresponding
> > > to
> > > + * freq_curr / freq_max.
> > I thought this is no longer the restriction and Vincent did some
> > work
> > to remove this restriction.
> If you're referring to the patch
> 23127296889f "sched/fair: Update scale invariance of PELT"
> merged in v5.2, I'm familiar with that and from my understanding you
> want a <1 scaling factor. This is my recalling of the patch:
> Vincent was studying some synthetic traces and realized that util_avg
> by PELT didn't quite match the result you'd get computing the formula
> with pen
> and paper (theoretical value). To address this he changed where the
> factor is applied in the PELT formula.
> At some point when accumulating the PELT sums, you'll have to measure
> the time
> 'delta' since you last updated PELT. What we have after Vincent's
> change is
> that this time length 'delta' gets itself scaled by the
> delta = time since last PELT update
> delta *= freq_percent
> In this way time goes at "wall clock speed" only when you're running
> at max
> capacitiy, and goes "slower" (from the PELT point of view) if we're
> running at
> a lower frequency. I don't think Vincent had in mind a faster-than-
> PELT time (which you'd get w/ freq_percent>1).
> Speaking of which, Srinivas, do you have any opinion and/or
> requirement about
> this? I confusely remember Peter Zijlstra saying (more than a year
> ago, now)
> that you would like an unclipped freq_curr/freq_max ratio, and may
> not be
> happy with this patch clipping it to 1 when freq_curr >
> 4_cores_turbo. If
> that's the case, could you elaborate on this?
> Ignore that if it doesn't make sense, I may be mis-remembering.
I was thinking of power efficiency use case particularly for Atom like
platforms, 1C max as you observed is more efficient.
But now sched deadline code is using arch_scale_freq_capacity(() to
calculate dl_se->runtime, where closer to deterministic value with all
cores, may be better, which will be scaled with base_freq.
next prev parent reply other threads:[~2019-09-19 23:55 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 2:42 [PATCH 0/2] Add support for frequency invariance for (some) x86 Giovanni Gherdovich
2019-09-09 2:42 ` [PATCH 1/2] x86,sched: Add support for frequency invariance Giovanni Gherdovich
2019-09-11 15:28 ` Doug Smythies
2019-09-13 20:58 ` Doug Smythies
2019-09-17 14:25 ` Giovanni Gherdovich
2019-09-19 14:42 ` Doug Smythies
2019-09-24 8:06 ` Mel Gorman
2019-09-24 17:52 ` Doug Smythies
2019-09-13 22:52 ` Srinivas Pandruvada
2019-09-17 14:27 ` Giovanni Gherdovich
2019-09-17 15:55 ` Vincent Guittot
2019-09-19 23:55 ` Srinivas Pandruvada [this message]
2019-09-14 10:57 ` Quentin Perret
2019-09-17 14:27 ` Giovanni Gherdovich
2019-09-17 14:39 ` Quentin Perret
2019-09-24 14:03 ` Peter Zijlstra
2019-09-24 16:00 ` Peter Zijlstra
2019-10-02 12:27 ` Giovanni Gherdovich
2019-10-02 18:45 ` Peter Zijlstra
2019-09-24 16:04 ` Peter Zijlstra
2019-10-02 12:26 ` Giovanni Gherdovich
2019-10-02 18:35 ` Peter Zijlstra
2019-09-24 16:30 ` Peter Zijlstra
2019-10-02 12:25 ` Giovanni Gherdovich
2019-10-02 18:47 ` Peter Zijlstra
2019-09-09 2:42 ` [PATCH 2/2] cpufreq: intel_pstate: Conditional frequency invariant accounting Giovanni Gherdovich
2019-09-24 16:01 ` [PATCH 0/2] Add support for frequency invariance for (some) x86 Peter Zijlstra
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