linux-kernel - Re: [PATCH 3/3] ARM: exynos_defconfig: Enable Energy Model framework

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Date:   Fri, 31 Jan 2020 14:16:34 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     lukasz.luba@....com
Cc:     kgene@...nel.org, linux-arm-kernel@...ts.infradead.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        Chanwoo Choi <cw00.choi@...sung.com>, robh+dt@...nel.org,
        mark.rutland@....com,
        Bartłomiej Żołnierkiewicz 
        <b.zolnierkie@...sung.com>, dietmar.eggemann@....com
Subject: Re: [PATCH 3/3] ARM: exynos_defconfig: Enable Energy Model framework

On Mon, 27 Jan 2020 at 22:55, <lukasz.luba@....com> wrote:
>
> From: Lukasz Luba <lukasz.luba@....com>
>
> Enable the Energy Model (EM) brings possibility to use Energy Aware
> Scheduler (EAS). This compiles the EM but does not enable to run EAS in
> default. The EAS only works with SchedUtil - a CPUFreq governor which
> handles direct requests from the scheduler for the frequency change. Thus,
> to make EAS working in default, the SchedUtil governor should be
> configured as default CPUFreq governor.

Full stop. That's enough of needed explanation of schedutil.

> Although, the EAS might be enabled
> in runtime, when the EM is present for CPUs, the SchedUtil is compiled and
> then set as CPUFreq governor, i.e.:
>
> echo schedutil > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> echo schedutil > /sys/devices/system/cpu/cpu4/cpufreq/scaling_governor
>
> To check if EAS is ready to work, the read output from the command below
> should show '1':
> cat /proc/sys/kernel/sched_energy_aware
>
> To disable EAS in runtime simply 'echo 0' to the file above.

Not related to this commit. If you were implemeting here
schedutil/EAS, then it makes sense to post all this. However what's
the point to describe it in every defconfig change?

> Some test results, which stress the scheduler on Odroid-XU3:
> hackbench -l 500 -s 4096
> With mainline code and with this patch set.

Skip the last sentence - duplicated information.

>
> The tests have been made with and without CONFIG_PROVE_LOCKING (PL)
> (which is set to =y in default exynos_defconfig)
>
>                 |               this patch set                  | mainline

The commit will be applied on its own branch so the meaning of "this
patch set" will be lost. Maybe just "before/after"?

>                 |-----------------------------------------------|---------------
>                 | performance   | SchedUtil     | SchedUtil     | performance
>                 | governor      | governor      | governor      | governor
>                 |               | w/o EAS       | w/ EAS        |
> ----------------|---------------|---------------|---------------|---------------
> hackbench w/ PL | 12.7s         | 11.7s         | 12.0s         | 13.0s - 12.2s
> hackbench w/o PL| 9.2s          | 8.1s          | 8.2s          | 9.2s - 8.4s

Why does the performance different before and after this patch?

Mention - lower better (?). Space between number and unit... or better
mention [s] in column title.

And last but not least:
Why this patch is separate from 1/3? I don't get the need of splitting them.

Best regards,
Krzysztof