linux-kernel - Re: [PATCH v3 4/7] thermal/drivers/tegra: Add driver for Tegra30 thermal sensor

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Message-ID: <57e044af-072f-cf7e-8f25-dc8b814c78c5@gmail.com>
Date:   Wed, 16 Jun 2021 13:49:18 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amitk@...nel.org>,
        Andreas Westman Dorcsak <hedmoo@...oo.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        Svyatoslav Ryhel <clamor95@...il.com>,
        Ihor Didenko <tailormoon@...bler.ru>,
        Ion Agorria <ion@...rria.com>,
        Matt Merhar <mattmerhar@...tonmail.com>,
        Peter Geis <pgwipeout@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-tegra@...r.kernel.org,
        "open list:THERMAL" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3 4/7] thermal/drivers/tegra: Add driver for Tegra30
 thermal sensor

16.06.2021 11:51, Vincent Guittot пишет:
> On Wed, 16 Jun 2021 at 10:39, Dmitry Osipenko <digetx@...il.com> wrote:
>>
>> 16.06.2021 11:30, Vincent Guittot пишет:
>>> On Wed, 16 Jun 2021 at 10:03, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>>>
>>>> +Vincent.
>>>>
>>>> On 15-06-21, 22:32, Dmitry Osipenko wrote:
>>>>> IIUC, the cpufreq already should be prepared for the case where firmware
>>>>> may override frequency. Viresh, could you please clarify what are the
>>>>> possible implications of the frequency overriding?
>>>>
>>>> The only implication is software would think hardware is running at
>>>> some other frequency, while it is not. Not sure if something may break
>>>> as a result of this.
>>>>
>>>> The scheduler's view of CPUs will not be same though, i.e. scheduler
>>>> will see capacity as X, while in reality it has changed to Y.
>>>
>>> thermal_pressure is used by scheduler to balance the load between CPUs
>>> according to the actual max frequency. If the thermal pressure doesn't
>>> reflect reality, scheduler will end up enqueuing too many  tasks on a
>>> throttle CPU.
>>
>> What if all CPUs are throttled equally and running on the same
>> frequency, will throttling have any effect on the scheduler decisions?
> 
> Yes, the capacity is also used to detect when CPUs have spare capacity
> or are already overloaded. We usually try to fill the spare capacity
> of a CPU (CPU's max capacity - current utilization) but he max
> capacity is reduced when the CPU is throttled, and the spare capacity
> doesn't exist but scheduler could try to it
> 

Thank you.