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Subject: Re: [RFC PATCH 0/7] Introduce thermal pressure
To:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thara Gopinath <thara.gopinath@linaro.org>,
        linux-kernel@vger.kernel.org
Cc:     mingo@redhat.com, peterz@infradead.org, rui.zhang@intel.com,
        gregkh@linuxfoundation.org, rafael@kernel.org,
        amit.kachhap@gmail.com, viresh.kumar@linaro.org,
        javi.merino@kernel.org, edubezval@gmail.com,
        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 09:35:08 +0200
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Hi Daniel,

On 10/10/2018 06:54 PM, Daniel Lezcano wrote:
> On 10/10/2018 17:35, 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%.
>>
>> 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?
> 
> aobench AFAICT
> 
> It would be interesting if you can share the thermal profile of your board.
> 
Thanks for the benchmark name.
It was tested on Samsung TM2 device with Exynos 5433 with debian.
Thermal stuff you can find in mainline:
arch/arm64/boot/dts/exynos/exynos5433-tmu.dtsi

Regards,
Lukasz

> 
>> On 10/09/2018 06:24 PM, Thara Gopinath wrote:
>>> Thermal governors can respond to an overheat event for a cpu by
>>> capping the cpu's maximum possible frequency. This in turn
>>> means that the maximum available compute capacity of the
>>> cpu is restricted. But today in linux kernel, in event of maximum
>>> frequency capping of a cpu, the maximum available compute
>>> capacity of the cpu is not adjusted at all. In other words, scheduler
>>> is unware maximum cpu capacity restrictions placed due to thermal
>>> activity. This patch series attempts to address this issue.
>>> The benefits identified are better task placement among available
>>> cpus in event of overheating which in turn leads to better
>>> performance numbers.
>>>
>>> The delta between the maximum possible capacity of a cpu and
>>> maximum available capacity of a cpu due to thermal event can
>>> be considered as thermal pressure. Instantaneous thermal pressure
>>> is hard to record and can sometime be erroneous as there can be mismatch
>>> between the actual capping of capacity and scheduler recording it.
>>> Thus solution is to have a weighted average per cpu value for thermal
>>> pressure over time. The weight reflects the amount of time the cpu has
>>> spent at a capped maximum frequency. To accumulate, average and
>>> appropriately decay thermal pressure, this patch series uses pelt
>>> signals and reuses the available framework that does a similar
>>> bookkeeping of rt/dl task utilization.
>>>
>>> Regarding testing, basic build, boot and sanity testing have been
>>> performed on hikey960 mainline kernel with debian file system.
>>> Further aobench (An occlusion renderer for benchmarking realworld
>>> floating point performance) showed the following results on hikey960
>>> with debain.
>>>
>>>                                           Result          Standard        Standard
>>>                                           (Time secs)     Error           Deviation
>>> Hikey 960 - no thermal pressure applied 138.67          6.52            11.52%
>>> Hikey 960 -  thermal pressure applied   122.37          5.78            11.57%
>>>
>>> Thara Gopinath (7):
>>>     sched/pelt: Add option to make load and util calculations frequency
>>>       invariant
>>>     sched/pelt.c: Add support to track thermal pressure
>>>     sched: Add infrastructure to store and update instantaneous thermal
>>>       pressure
>>>     sched: Initialize per cpu thermal pressure structure
>>>     sched/fair: Enable CFS periodic tick to update thermal pressure
>>>     sched/fair: update cpu_capcity to reflect thermal pressure
>>>     thermal/cpu-cooling: Update thermal pressure in case of a maximum
>>>       frequency capping
>>>
>>>    drivers/base/arch_topology.c  |  1 +
>>>    drivers/thermal/cpu_cooling.c | 20 ++++++++++++-
>>>    include/linux/sched.h         | 14 +++++++++
>>>    kernel/sched/Makefile         |  2 +-
>>>    kernel/sched/core.c           |  2 ++
>>>    kernel/sched/fair.c           |  4 +++
>>>    kernel/sched/pelt.c           | 40 ++++++++++++++++++--------
>>>    kernel/sched/pelt.h           |  7 +++++
>>>    kernel/sched/sched.h          |  1 +
>>>    kernel/sched/thermal.c        | 66 +++++++++++++++++++++++++++++++++++++++++++
>>>    kernel/sched/thermal.h        | 13 +++++++++
>>>    11 files changed, 157 insertions(+), 13 deletions(-)
>>>    create mode 100644 kernel/sched/thermal.c
>>>    create mode 100644 kernel/sched/thermal.h
>>>
> 
>