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

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Message-ID: <08aff2de-85d5-36b2-13bb-bad6eb5d37eb@samsung.com>
Date:   Fri, 31 Jan 2020 14:47:32 +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 2:31 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. ]

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

> Best regards,
> Krzysztof