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

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Date:   Fri, 31 Jan 2020 14:31:26 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     lukasz.luba@....com, 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, dietmar.eggemann@....com
Subject: Re: [PATCH 3/3] ARM: exynos_defconfig: Enable Energy Model framework

On Fri, 31 Jan 2020 at 14:30, Bartlomiej Zolnierkiewicz
<b.zolnierkie@...sung.com> wrote:
>
>
> Hi,
>
> On 1/27/20 10:54 PM, 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. 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.
> >
> > Some test results, which stress the scheduler on Odroid-XU3:
> > hackbench -l 500 -s 4096
> > With mainline code and with this patch set.
> >
> > 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
> >               |-----------------------------------------------|---------------
> >               | 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
>
> Would you happen to have measurements of how much power is
> saved by running hackbench using "SchedUtil governor w/ EAS"
> instead of "SchedUtil governor w/o EAS"?

That's a good point and quite important reason behind enabling (or not) EAS...

Best regards,
Krzysztof