linux-kernel - Re: [RFC] [PATCH] cpufreq: allow full selection of default governors

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Message-ID: <20070427015410.GA9650@isilmar.linta.de>
Date:	Thu, 26 Apr 2007 21:54:10 -0400
From:	Dominik Brodowski <linux@...inikbrodowski.net>
To:	Dave Jones <davej@...hat.com>,
	Nish Aravamudan <nish.aravamudan@...il.com>,
	William Heimbigner <icxcnika@....tar.cc>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] [PATCH] cpufreq: allow full selection of default governors

On Tue, Apr 24, 2007 at 08:03:27PM -0400, Dave Jones wrote:
> On Tue, Apr 24, 2007 at 03:05:36PM -0700, Nish Aravamudan wrote:
>  > On 4/24/07, Dave Jones <davej@...hat.com> wrote:
>  > > On Tue, Apr 24, 2007 at 09:03:23PM +0000, William Heimbigner wrote:
>  > >  > The following patches should allow selection of conservative, powersave, and
>  > >  > ondemand in the kernel configuration.
>  > >
>  > > This has been rejected several times already.
>  > > Ondemand and conservative isn't a viable governor for all cpufreq
>  > > implementations (ie, ones with high switching latencies).
>  > 
>  > This piques my curiosity -- some governors don't work with some
>  > cpufreq implementations. Are those implementations in the kernel or in
>  > userspace? If in the kernel, then perhaps there should be some
>  > dependency expressed there in Kconfig between cpufreq implementation
>  > and the available governors
> 
> it can't be solved that easily. powernow-k8 for example is fine to
> use with ondemand on newer systems, where the latency is low.
> On older models however, it isn't.
> 
>  > > Also, see the
>  > > comment in the Kconfig a few lines above where you are adding this.
>  > 
>  > Are these governors unfixable? If
> 
> tbh, I've forgotten the original issues that caused the comment
> to be placed there. Dominik ?

Not unfixable, but: cpufreq is currently[*] built around the assumption that
at least one governor is correctly initialized or can be brought to work
when a CPU is registered with the cpufreq core.

	Dominik


[*] That is, the last time I looked at it ;)
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