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

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Message-ID: <20070427122444.GA3714@isilmar.linta.de>
Date:	Fri, 27 Apr 2007 08:24:44 -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 Fri, Apr 27, 2007 at 02:09:57AM -0400, Dave Jones wrote:
> On Thu, Apr 26, 2007 at 09:54:10PM -0400, Dominik Brodowski wrote:
>  > 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.
> 
> It would have to take something fairly spectacular though for performance or
> powersave to fail registration. Can you remember why we chose not to allow those?

performance _is_ allowed; powersave would be possible -- but then those who
accidentally enable it on elanfreq might wait 100 times as long for the
system to boot, with gx-suspmod it might even be 255 times as long -- okay,
by default it's just 20 times as long, but still...

	Dominik
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