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

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Message-ID: <003d01d5a63d$f6ab3950$e401abf0$@net>
Date:   Thu, 28 Nov 2019 14:48:27 -0800
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Giovanni Gherdovich'" <ggherdovich@...e.cz>
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>,
        "'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

Summary: There never was an issue here.

Sorry for the noise of this thread, and the resulting waste of time.

On 2019.11.26 23:33 Doug Smythies wrote:
> On 2019.11.26 07:20 Giovanni Gherdovich wrote:
>> On Mon, 2019-11-25 at 21:59 -0800, Doug Smythies wrote:
>>> [...]
>>> The issue with the schedutil governor not working properly in the 5.4 RC series
>>> appears to be hardware dependant.

No it 's not.

Issues with my Sandy Bridge, i7-2600K, test computer and kernel 5.4
seem to be because it is running an older Ubuntu server version,
apparently somewhat dependant on cgroup V1 and their cgmanager package.
I am unable to remove the package to test further because I do use VMs
that seem to depend on it.

In the kernel configuration when CONFIG_UCLAMP_TASK_GROUP=y
the computer behaves as though the new parameter "cpu.uclamp.min"
is set to max rather than 0, but I can not prove it.

>>> 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:

I failed to mention that was brand new Ubuntu server 20.04 development version
installation, which turns out to have been an important omission.

>>> 
>>> 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.

I took the disk from the Haswell computer and put it in the Sandy Bridge
computer, and then everything was fine:

Kernel 5.4 intel_cpufreq/schedutil: 3636 seconds
Kernel 5.4 + gg 6 intel_cpufreq/schedutil: 2427.6 seconds
Ratio: 0.67 which is consistent with previous Sandy Bridge results

...

Those above kernels included:

CONFIG_UCLAMP_TASK_GROUP=y

Which cause my older Ubuntu server edition using the 
intel_cpufreq/schedutil to respond much like the performance
governor, as reported the other day and above.

I also booted the Sandy Bridge computer, with its original disk,
with the kernel command line containing:

cgroup_no_v1=all

and, while it complained during boot, it did work as expected
using the intel_cpufreq/schedutil driver/governor.

... Doug