linux-kernel - Re: [PATCH] thermal: of: Allow selection of thermal governor in DT

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Date:   Thu, 8 Mar 2018 11:05:55 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Ram Chandrasekar <rkumbako@...eaurora.org>,
        DTML <devicetree@...r.kernel.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal: of: Allow selection of thermal governor in DT

On Thu, Mar 8, 2018 at 10:19 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On Wed, Mar 7, 2018 at 4:29 PM, Amit Kucheria <amit.kucheria@...aro.org> wrote:
>> Cpufreq/cpuidle are designed to control a single parameter while
>> thermal framework is trying to mitigate heat from several disparate
>> sources that are throttled in different ways. Besides, cpufreq/cpuidle
>> have somewhat mature governors. Cpuidle has only one governor (for
>> tickless) - menu governor, cpufreq has ondemand in mainline, replaced
>> by interactive in android and hopefully soon both will be replaced by
>
> Interactive and schedfreq are already removed from Android 4.4 and 4.9.
> It used schedutil now.

Good to hear.

>> schedutil.
>>
>> Badly configured cpufreq/cpuidle/devfreq only leads to wasted power,
>> while badly configured thermal zone leads to the loss of operation
>> e.g. reboots, too hot to touch, etc.
>
> I don't think such heat-ups will happen right during boot, where some
> init.rc should
> come up and change the governor.

Interestingly enough, there are some patches that make the thermal
framework start earlier to deal with boot-time thermal issues. I
expect to post them soon. :-) These are required, for example, if the
device goes into a reboot loop - the device might not even make it to
the point in userspace where the governors are setup. In such a loop,
the temperature constantly keeps increasing.

> Over that if we are worried about production images only, then what prevents us
> to select the right default governor in the defconfig ? We shouldn't
> be worried about
> multi-platform kernels for production images.

I was refering to the 'make defconfig' out-of-box experience that
makes the majority of developer boards/devices out there stable to
work on. I can't do that today.

Regards,
Amit