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Subject: Re: [RFC PATCH 0/7] Introduce thermal pressure
To:     Thara Gopinath <thara.gopinath@linaro.org>,
        linux-kernel@vger.kernel.org
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        gregkh@linuxfoundation.org, rafael@kernel.org,
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        javi.merino@kernel.org, edubezval@gmail.com,
        daniel.lezcano@linaro.org, linux-pm@vger.kernel.org,
        quentin.perret@arm.com, ionela.voinescu@arm.com,
        vincent.guittot@linaro.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
From:   Lukasz Luba <l.luba@partner.samsung.com>
Date:   Thu, 11 Oct 2018 13:10:23 +0200
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On 10/10/2018 07:30 PM, Thara Gopinath wrote:
> Hello Lukasz,
> 
> On 10/10/2018 11:35 AM, Lukasz Luba wrote:
>> Hi Thara,
>>
>> I have run it on Exynos5433 mainline.
>> When it is enabled with step_wise thermal governor,
>> some of my tests are showing ~30-50% regression (i.e. hackbench),
>> dhrystone ~10%.
> 
> That is interesting. If I understand correctly, dhrystone spawns 16
> threads or so and floods the system. In "theory", such a test should not
> see any performance improvement and degradation. What is the thermal
> activity like in your system? I will try running one of these tests on
> hikey960.
I use this dhrystone implementation:
https://github.com/Keith-S-Thompson/dhrystone/blob/master/v2.2/dry.c
It does not span new threads/processes and I pinned it to a single cpu.

My thermal setup is probably different than yours.
You have (on hikey960) probably 1 sensor for whole SoC and one thermal
zone (if it is this mainline file:
arch/arm64/boot/dts/hisilicon/hi3660.dtsi).
This thermal zone has two cooling devices - two clusters with dvfs.
Your temperature signal read out from that sensor is probably much
smoother. When you have sensor inside cluster, the rising factor
can be even 20deg/s (for big cores).
In my case, there are 4 thermal zones, each cluster has it's private
sensor and thermal zone. There is no 'SoC sensor' or 'PCB sensor',
which is recommended for IPA.
>>
>> Could you tell me which thermal governor was used in your case?
>> Please also share the name of that benchmark, i will give it a try.
>> Is it single threaded compute-intensive?
> 
> Step-wise governor.
> I use aobench which is part of phoronix-test-suite.
> 
> Regards
> Thara
> 
I have built this aobench and run it pinned to single big cpu:
time taskset -c 4 ./aobench
The results:
3min-5:30min [mainline]
5:15min-5:50min [+patchset]

The idea is definitely worth to investigate further.

Regards,
Lukasz