Bug#421879: cpufreq_ondemand: cpufreq_ondemand responds too slowly

[Mattia Dongili <malattia@linux.it>]

On Wed, May 02, 2007 at 03:44:30PM +0100, Greg Kochanski wrote:
> Mattia Dongili wrote:
> >On Wed, May 02, 2007 at 09:36:27AM +0100, Greg Kochanski wrote:
> >...
> >>Suggestions:
> >>1)   allow sampling_rate_min to be set to smaller values, like 0.1 second.
> >>     The default sampling_rate_min should probably be 0.25 seconds.
> >>     If that were the case, the CPU would power up before
> >>      a window drag (or similar motion) was finished, and the response 
> >>      would
> >>      probably seem acceptably snappy.
> >
> >actually the sampling rate is dependent on the transition latency for
> >the processor.
> 
> Can you explain further?

assume your processor takes 100ms to switch from one frequency to
another. Ondemand takes this value as a base to calculate the polling
frequency (min, max et al.) and to avoid the possibility to clog the
system with to many transitions it sets a lower value that is a multiple
of the transition latency.

> >>2) Make the default scaling_min_freq be somewhat larger, perhaps 670 MHz 
> >>or
> >>   20% of the max clock speed.    This will (of course) reduce laptop 
> >>   life,
> >>   but I suspect that it won't make a noticeable change.
> >
> >you can already do that by setting /etc/default/cpufrequtils from the
> >cpufrequtils package.
> >
> >cheers
> 
> 
> Yes, you can.   However, I was arguing for a change in the defaults,
> so that the average user would get a better performance with the
> default settings.

this bug then belongs to the package that sets ondemand as default
governor, which isn't the kernel.

cheers
-- 
mattia
:wq!