linux-kernel - Re: [Patch v9 5/8] sched/fair: update cpu

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Date:   Fri, 14 Feb 2020 09:52:46 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Amit Kucheria <amit.kucheria@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, ionela.voinescu@....com,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Zhang Rui <rui.zhang@...el.com>, qperret@...gle.com,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Juri Lelli <juri.lelli@...hat.com>, corbet@....net,
        LKML <linux-kernel@...r.kernel.org>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>
Subject: Re: [Patch v9 5/8] sched/fair: update cpu_capacity to reflect thermal
 pressure

On 02/13/2020 08:39 AM, Amit Kucheria wrote:
> On Wed, Jan 29, 2020 at 4:06 AM Thara Gopinath
> <thara.gopinath@...aro.org> wrote:
>>
>> cpu_capacity initially reflects the maximum possible capacity of a cpu.
>> Thermal pressure on a cpu means this maximum possible capacity is
>> unavailable due to thermal events. This patch subtracts the average thermal
>> pressure for a cpu from its maximum possible capacity so that cpu_capacity
>> reflects the actual maximum currently available capacity.
> 
> "actual maximum currently available capacity" is quite a mouthful. :-)
> 
> "Remaining capacity" or "Effective capacity" anyone?

"Remaining maximum capacity"?

> 
> IIUC, this remaining capacity is NOT the same as the capped/decreased
> capacity referred to in patches 1 and 3. The delta capacity (aka
> thermal pressure) there refers to the difference between HW max
> capacity and thermally throttled capacity.
> Here, we also subtract RT/DL utilisation. Is that accurate?

Yes, here we do subtract RT/DL utilization as well. But from the thermal
pressure point of view, it is immaterial. I am not touching the code
that subtracts RT/DL utilization , I am just adding thermal pressure to
the variables that has to be deducted from the stated max capacity to
reflect the actual capacity. So as far as this patch series is
concerned, capped/decreased capacity is the same across all
patches.(Though there is the instantaneous capped capacity and the
time-averaged capped capacity)


-- 
Warm Regards
Thara