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

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Message-ID: <20191224110834.rgibtqm6dr6kmu5y@e107158-lin.cambridge.arm.com>
Date:   Tue, 24 Dec 2019 11:08:35 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     'Giovanni Gherdovich' <ggherdovich@...e.cz>, 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>,
        'Peter Zijlstra' <peterz@...radead.org>,
        'Vincent Guittot' <vincent.guittot@...aro.org>,
        'Quentin Perret' <qperret@...rret.net>,
        'Dietmar Eggemann' <dietmar.eggemann@....com>,
        'Srinivas Pandruvada' <srinivas.pandruvada@...ux.intel.com>,
        'Thomas Gleixner' <tglx@...utronix.de>,
        'Ingo Molnar' <mingo@...hat.com>,
        'Borislav Petkov' <bp@...e.de>, 'Len Brown' <lenb@...nel.org>,
        "'Rafael J . Wysocki'" <rjw@...ysocki.net>
Subject: Re: [PATCH v4 1/6] x86,sched: Add support for frequency invariance

On 12/23/19 17:16, Doug Smythies wrote:
> Yes, it fixes the schedutil governor behaving like the performance governor
> problem on my i7-2600K test system.
> 
> I re-ran the tests several times, and re-booted back to the stock (problem)
> kernel to verify incorrect schedutil governor performance (i.e. I toggled
> back and forth, 2 times for each of 2 kernels, tests 1 and 2, total 8 tests).
> Kernel 5.5-rc2: 4 tests FAILED (as expected).
> Kernel 5.5-rc2 + this patch: 4 tests PASSED.

Great! Thanks for testing it, I'll send a proper patch shortly.

> 
> Accidentally tested:
> Kernel 5.5-rc2 + this patch + command line "cgroup_no_v1=all": 1 test PASS.

I think this cgroup_no_v1 is a happy accident. It has nothing to do with the
fault, but for your case maybe helped observing things in a better way. FWIW,
I reproduced the issue on Juno Arm64 using Debian and Buildroot rootfs.

What is actually required to trigger the bug is to create a cpu controller and
add all system tasks to it to create some noise - which Ubuntu and Debian do by
default at boot time. In Buildroot when I did that manually I could see the
frequency going to max most of the time.

I'll add away to test this scenario.

Thanks for your detailed report.

Happy holidays!

--
Qais Yousef