linux-kernel - RE: [PATCH v4 1/6] x86,sched: Add support for frequency invariance

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Date:   Mon, 25 Nov 2019 21:59:19 -0800
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Giovanni Gherdovich'" <ggherdovich@...e.cz>,
        "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>,
        "'Thomas Gleixner'" <tglx@...utronix.de>,
        "'Ingo Molnar'" <mingo@...hat.com>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "'Borislav Petkov'" <bp@...e.de>, "'Len Brown'" <lenb@...nel.org>,
        "'Rafael J . Wysocki'" <rjw@...ysocki.net>
Cc:     <x86@...nel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "'Mel Gorman'" <mgorman@...hsingularity.net>,
        "'Matt Fleming'" <matt@...eblueprint.co.uk>,
        "'Viresh Kumar'" <viresh.kumar@...aro.org>,
        "'Juri Lelli'" <juri.lelli@...hat.com>,
        "'Paul Turner'" <pjt@...gle.com>,
        "'Vincent Guittot'" <vincent.guittot@...aro.org>,
        "'Quentin Perret'" <qperret@...rret.net>,
        "'Dietmar Eggemann'" <dietmar.eggemann@....com>
Subject: RE: [PATCH v4 1/6] x86,sched: Add support for frequency invariance

On 2019.11.25 08:06 Giovanni Gherdovich wrote:
> On Sat, 2019-11-23 at 23:49 -0800, Doug Smythies wrote:
>> ...
>> Kernel 5.4-rc8 + revert, intel_cpufreq/schedutil: 3899 seconds
>> Kernel 5.4-rc8 + gg 6 + revert, intel_cpufreq/schedutil: 2740.7 seconds
>> Ratio: 0.70 (as expected)
>> Kernel 5.4-rc8, intel_cpufreq/schedutil: 2334.7 seconds (faster than expected)
>> Kernel 5.4-rc8 + gg 6 patch set, intel_cpufreq/schedutil: 2275.0 seconds (faster than expected)
>> Ratio: 0.97 (not as expected)
>> Kernel 5.4-rc8, intel_cpufreq/performance: 2215.3 seconds
>> Kernel 5.4-rc8, intel_cpufreq/ondemand: 3286.3 seconds
>> Re-stated from previous e-mail:
>> Kernel 5.3-rc8, intel_cpufreq/schedutil: ratio: 0.69 (I don't have the original times)
>
> Hello Doug,
>
> schedutil in 5.4 going a lot faster than in 5.3 would be a surprise. I'm
> running that same test too to check if I can see it as well.

Great, thanks. But see below.

>
> Besides, as it's already been said this patchset adds frequency
> scale-invariance to scheduler metrics such as load and utilization and that's
> useful also in areas other than frequency scaling (most notably the scheduler
> load balancer).

The issue with the schedutil governor not working properly in the 5.4 RC series
appears to be hardware dependant.

My test computer is Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz., Sandy Bridge.
On a temporary basis, I acquired a computer with an
Intel(R) Core(TM) i5-4460 CPU @ 3.20GHz, Haswell,
and schedutil governor behaviour with the exact same kernels is fine:

That "gitsource" test, "make test" 6 times, first run thrown out:

Kernel 5.4 intel_cpufreq/schedutil: 3411.8 seconds
Kernel 5.4 + gg 6 intel_cpufreq/schedutil: 1696.7 seconds
Ratio: 0.49
Recall you got a ratio of 0.49 with 5th generation, Broadwell.

... Doug