linux-kernel - Re: [Patch v8 1/7] sched/pelt: Add support to track thermal pressure

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Message-ID: <26e7d02f-3ecf-5769-424f-62fb98fe3ec2@arm.com>
Date:   Tue, 28 Jan 2020 17:15:12 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Thara Gopinath <thara.gopinath@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, ionela.voinescu@....com,
        vincent.guittot@...aro.org, rui.zhang@...el.com,
        qperret@...gle.com, daniel.lezcano@...aro.org,
        viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
        amit.kachhap@...il.com, javi.merino@...nel.org,
        amit.kucheria@...durent.com
Subject: Re: [Patch v8 1/7] sched/pelt: Add support to track thermal pressure

On 28/01/2020 14:32, Thara Gopinath wrote:
> On 01/27/2020 04:28 AM, Dietmar Eggemann wrote:
>> On 24/01/2020 20:07, Thara Gopinath wrote:
>>> On 01/23/2020 02:15 PM, Dietmar Eggemann wrote:
>>>> On 16/01/2020 16:17, Peter Zijlstra wrote:
>>>>> On Tue, Jan 14, 2020 at 02:57:33PM -0500, Thara Gopinath wrote:
>>
>> [...]
>>
>>>>>> +#ifdef CONFIG_HAVE_SCHED_THERMAL_PRESSURE
>>>>
>>>> I assume your plan is to enable this for Arm and Arm64? Otherwise the
>>>> code in 3/7 should also be guarded by this.
>>>
>>> Yes. I think it should be enabled for arm and arm64. I can submit a
>>> patch after this series is accepted to enable it.
>>> Nevertheless , I don't understand why is patch 3/7 tied with this.
>>> This portion is the averaging of thermal pressure. Patch 3/7 is to store
>>> and retrieve the instantaneous value.
>>
>> 3/7 is the code which overwrites the scheduler default
>> arch_cpu_thermal_pressure() [include/linux/sched/topology.h]. I see it
>> more of the engine to drive  thermal pressure tracking in the scheduler.
>>
>> So all the code in 3/7 only makes sense if HAVE_SCHED_THERMAL_PRESSURE
>> is selected by the arch. IMHO, 3/7 and enabling it for Arm/Arm64 should
>> go in together.
> Hi Dietmar,
> I will have to respectfully disagree here. We explicitly separated out
> this stuff (updating and reading of instantaneous thermal pressure)from
> scheduler. To me putting all this under HAVE_SCHED_THERMAL_PRESSURE is
> equivalent to keeping this stuff in scheduler specific code. But I will
> provide a patch enabling the option HAVE_SCHED_THERMAL_PRESSURE in
> arm64/defconfig. arm is trickier though as it has a bunch of SoC
> defconfigs. I will leave it out for now .

If you enable HAVE_SCHED_THERMAL_PRESSURE for Arm64 w/ this patch-set
then I don't see any disagreement here.