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

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Message-ID: <c03d1bd00704271006h4af83a0p99c37c6416b4c846@mail.gmail.com>
Date:	Fri, 27 Apr 2007 22:36:48 +0530
From:	"Gautham Shenoy" <ego.lkml@...il.com>
To:	"Dominik Brodowski" <linux@...inikbrodowski.net>,
	"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>,
	Dhaval <dhaval.giani@...il.com>
Subject: Re: [RFC] [PATCH] cpufreq: allow full selection of default governors

On 4/27/07, Dominik Brodowski <linux@...inikbrodowski.net> wrote:
> 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...

I agree!

Let a stable governor like performance or userspace be the default to
get the cpufreq up and running during boot up, and later on have some
init script switch
to a preferred governor like powersave/ondemand/conservative.

Changing governor is just a matter of loading the appropriate module
and echoing the appropriate value into
/sys/devices/*/cpufreq/scaling_governor. Hardly takes any time.

William, Is there a specific reason why you would want
powersave/ondemand/conservative to be activate during the system boot
up?

>
>         Dominik
> -
Regards
gautham.
-
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