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

Dominik Brodowski
2007-04-27T12:24:47Z

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@redhat.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