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

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Date:   Fri, 31 Jan 2020 14:48:55 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
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 1/31/20 2:47 PM, Bartlomiej Zolnierkiewicz wrote:
> 
> On 1/31/20 2:31 PM, Krzysztof Kozlowski wrote:
>> 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...
> 
> IIUC EAS is enabled by default if you use SchedUtil
> governor and Energy Model is available on you platform.
> 
> [ SchedUtil governor is enabled in exynos_defconfig
>   although not enabled by default currently. ]

s/enabled/used/

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics