Re: 2.6.17-rc3: cpufreq-set -g ondemand does not work
On Tue, 2006-05-16 at 14:54 +0200, Michael Schmitz wrote:
> > > Maybe this helps:
> > > http://forums.gentoo.org/viewtopic-t-462417.html
> > Yes, it does.
> > "JoseJX" write there that ondemand and conservative cannot be used
> > on 7xx/74xx processors because of the time required to switch speeds.
> The reason seems to be a rather conservative assumption on the latency
> ('probably takes forever') - does it really take more than 10 ms to switch
> speeds? The code path on the 7447A models appears to have a settle delay
> of 1 ms after the feature call (which boils down to an OUTB, basically),
> another 0.1 ms after the low_choose_7447a_dfs call which shouldn't take
> very long either. Am I missing something, Ben?
I'm being over conservative bcs of the voltage change
> I'd not be surprised if the latency was as low as 2 ms total - can we
> profile this reliably in some way? I guess I'll just set the latency to 5
> ms and see what happens ...
Last time I looked the on-demand governor was using a workqueue...
anything that has a latency of more than a few dozen usec in a workqueue
shall be shot...