cpufreq 'choice' Kconfig oddness in 2.6.22-rc6-mm1..

cpufreq 'choice' Kconfig oddness in 2.6.22-rc6-mm1..

[Valdis.Kletnieks]

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So I was looking at drivers/cpufreq/Kconfig, and wondering...

Is there a specific reason why we have a 'choice' clause that allows selecting
'performance' or 'userspace' as the default governor, and no obvious way to
select powersave, ondemand, or conservative as a default? Or was this an
oversight I should cook up a patch for?  Looks like the Kconfig and a bit
of cut-n-paste in include/linux/cpufreq.h is all that's needed?




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Re: cpufreq 'choice' Kconfig oddness in 2.6.22-rc6-mm1..

[Mattia Dongili]

On Sat, Jul 07, 2007 at 12:35:10AM -0400, Valdis.Kletnieks@vt.edu wrote:
> So I was looking at drivers/cpufreq/Kconfig, and wondering...
> 
> Is there a specific reason why we have a 'choice' clause that allows selecting
> 'performance' or 'userspace' as the default governor, and no obvious way to
> select powersave, ondemand, or conservative as a default? Or was this an

Yes, ondemand and conservative may refuse to load/work on systems with
a high transition latency and that is sometimes discovered only at
runtime. This makes them not selectable as default governors.

> oversight I should cook up a patch for?  Looks like the Kconfig and a bit
> of cut-n-paste in include/linux/cpufreq.h is all that's needed?

No, some more work is needed (e.g.: falling back to a different governor
if the selected fails). Thomas Renninger has posted patches on
cpufreq-devel to accomplish that.

cheers
-- 
mattia
:wq!

Re: cpufreq 'choice' Kconfig oddness in 2.6.22-rc6-mm1..

[Valdis.Kletnieks]

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On Sat, 07 Jul 2007 15:50:01 +0900, Mattia Dongili said:
> On Sat, Jul 07, 2007 at 12:35:10AM -0400, Valdis.Kletnieks@vt.edu wrote:
> > So I was looking at drivers/cpufreq/Kconfig, and wondering...
> > 
> > Is there a specific reason why we have a 'choice' clause that allows selecting
> > 'performance' or 'userspace' as the default governor, and no obvious way to
> > select powersave, ondemand, or conservative as a default? Or was this an
> 
> Yes, ondemand and conservative may refuse to load/work on systems with
> a high transition latency and that is sometimes discovered only at
> runtime. This makes them not selectable as default governors.

D'Oh! :)  I was trying to set ondemand as the default, only after verifying
that ondemand works as desired on my laptop.  I forgot that we probably need
to also allow for people who don't test before making things default....

> > oversight I should cook up a patch for?  Looks like the Kconfig and a bit
> > of cut-n-paste in include/linux/cpufreq.h is all that's needed?
> 
> No, some more work is needed (e.g.: falling back to a different governor
> if the selected fails). Thomas Renninger has posted patches on
> cpufreq-devel to accomplish that.

OK - I'll keep an eye open and test them out whenever they hit -mm.
In the meantime, an 'echo ondemand' into the right /sys file is working
for me as a workaround.


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