linux-kernel - Re: [PATCH] arm64: defconfig: Select schedutil as default cpufreq governor

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Message-ID: <edbb7a2b-7f84-c32f-1b03-daafcfaca67d@arm.com>
Date:   Tue, 19 Dec 2017 18:30:11 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>, arm@...nel.org,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: defconfig: Select schedutil as default cpufreq
 governor

On 18/12/17 04:29, Viresh Kumar wrote:
> On 15-12-17, 15:50, Catalin Marinas wrote:
>> On Thu, Nov 16, 2017 at 11:51:36AM +0530, Viresh Kumar wrote:
>>> Currently performance governor is getting selected by default, which is
>>> surely not a very good choice as its pretty much power hungry.
>>>
>>> Select schedutil instead.
>>
>> And why do we care about this in defconfig? People deploying their own
>> kernels in mobile may opt for this config, others may prefer the default
>> governor.
>>
>> Also it seems it would be the only architecture make this governor the
>> default, so NAK.
> 
> This is a bit dangerous configuration IMHO.
> 
> Other architectures have some *real* governor selected by default, like Ondemand
> or Conservative. Running your CPUs at max (because of the default performance
> governor in arm64 config) may end up burning some SoCs accidentally just because
> their thermal stuff doesn't kick in to cool SoC down properly.

Honestly, this feels like widening a road because someone wants to drive
a car with no steering wheel. If an SoC is broken enough not to to into
thermal throttling on its own, I'm tempted to say "let it burn".

And on-demand is just as bad as performance in that respect, as it will
to the same thing as soon as you run (for example) Firefox. Or Emacs.

> So, we should have one of ondemand, conservative and schedutil selected by
> default for arm64 as well IMO and schedutil is the one which every one is
> falling back to now a days, even android.

I'll have my bike shed painted pink, thank you very much! :-)

	M.
-- 
Jazz is not dead. It just smells funny...