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From: Peter Zijlstra <peterz@infradead.org>
To: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Jon Grimm <Jon.Grimm@amd.com>,
	Nathan Fontenot <Nathan.Fontenot@amd.com>,
	Yazen Ghannam <Yazen.Ghannam@amd.com>,
	Thomas Lendacky <Thomas.Lendacky@amd.com>,
	Suthikulpanit Suravee <Suravee.Suthikulpanit@amd.com>,
	Mel Gorman <mgorman@techsingularity.net>, Pu Wen <puwen@hygon.cn>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Michael Larabel <Michael@phoronix.com>,
	x86@kernel.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: Re: [PATCH v2 1/1] x86,sched: On AMD EPYC set freq_max = max_boost in schedutil invariant formula
Date: Mon, 25 Jan 2021 11:04:08 +0100	[thread overview]
Message-ID: <YA6XmO2nuivdpE8M@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210122204038.3238-2-ggherdovich@suse.cz>

On Fri, Jan 22, 2021 at 09:40:38PM +0100, Giovanni Gherdovich wrote:
> This workload is constant in time, so instead of using the PELT sum we can
> pretend that scale invariance is obtained with
> 
>     util_inv = util_raw * freq_curr / freq_max1        [formula-1]
> 
> where util_raw is the PELT util from v5.10 (which is to say, not invariant),
> and util_inv is the PELT util from v5.11-rc4. freq_max1 comes from
> commit 976df7e5730e ("x86, sched: Use midpoint of max_boost and max_P for
> frequency invariance on AMD EPYC") and is (P0+max_boost)/2 = (2.25+3.4)/2 =
> 2.825 GHz.  Then we have the schedutil formula
> 
>     freq_next = 1.25 * freq_max2 * util_inv            [formula-2]
> 
> Here v5.11-rc4 uses freq_max2 = P0 = 2.25 GHz (and this patch changes it to
> 3.4 GHz).
> 
> Since all cores are busy, there is no boost available. Let's be generous and say
> the tasks initially get P0, i.e. freq_curr = 2.25 GHz. Combining the formulas
> above and taking util_raw = 825/1024 = 0.8, freq_next is:
> 
>     freq_next = 1.25 * 2.25 * 0.8 * 2.25 / 2.825 = 1.79 GHz

Right, so here's a 'problem' between schedutil and cpufreq, they don't
use the same f_max at all times.

And this is also an inconsistency between acpi_cpufreq and intel_pstate
(passive). IIRC the intel_pstate cpufreq drivers uses 4C/1C/P0 resp,
while ACPI seems to stick to P0 f_max.

Rafael; should ACPI change that behaviour rather than adding yet another
magic variable?

  reply	other threads:[~2021-01-25 10:22 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-22 20:40 [PATCH v2 0/1] AMD EPYC: fix schedutil perf regression (freq-invariance) Giovanni Gherdovich
2021-01-22 20:40 ` [PATCH v2 1/1] x86,sched: On AMD EPYC set freq_max = max_boost in schedutil invariant formula Giovanni Gherdovich
2021-01-25 10:04   ` Peter Zijlstra [this message]
2021-01-26  9:28     ` Giovanni Gherdovich
2021-01-26 10:02       ` Peter Zijlstra
2021-02-02 18:45       ` Rafael J. Wysocki
2021-02-02 19:11         ` Rafael J. Wysocki
2021-02-03  9:56           ` Giovanni Gherdovich
2021-02-02 18:40     ` Rafael J. Wysocki
2021-01-25 10:06   ` Peter Zijlstra
2021-01-26  9:09     ` Giovanni Gherdovich
2021-01-26  9:31       ` Mel Gorman
2021-01-26 10:05         ` Peter Zijlstra
     [not found]           ` <1611933781.15858.48.camel@suse.cz>
2021-02-02 14:17             ` Giovanni Gherdovich
2021-02-02 18:21               ` Peter Zijlstra
2021-02-02 18:29                 ` Rafael J. Wysocki
2021-02-02 19:00                   ` Rafael J. Wysocki
2021-02-02 18:59   ` Rafael J. Wysocki
2021-02-02 19:26     ` Rafael J. Wysocki
2021-02-03  8:39       ` Giovanni Gherdovich
2021-02-03 13:40         ` Rafael J. Wysocki
2021-02-03  9:12     ` Giovanni Gherdovich
2021-02-03  6:04   ` Viresh Kumar
2021-01-24 22:30 ` [PATCH v2 0/1] AMD EPYC: fix schedutil perf regression (freq-invariance) Michael Larabel
2021-01-25  8:34   ` Peter Zijlstra
2021-01-26  9:01     ` Giovanni Gherdovich

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