Re: Overall picture of cpufreq..

[Thomas Renninger <trenn@suse.de>]

On Mon, 2008-01-14 at 08:08 +0100, Tomasz Chmielewski wrote:
> Saru Addep schrieb:
> > Hi Thomas,
> > 
> > So that means if we have an ondemand governor properly instrumented, there
> > is no need to have userspace governor. In the case of ondemand governor, the
> > only work that will be left to userspace would be to set the min, and max
> > freq. The complete intelligence of DVFS algoritm is present inside the
> > ondemand governor. Is my understanding correct.

Yes, this is correct.

> It looks to me that ondemand governor doesn't have "the complete 
> intelligence".
> 
> For example, it doesn't detect CPU load coming from some kernel tasks, 
> like kcryptd: reads/writes from a device crypted with dm-crypt will be 
> very slow if one uses the ondemand governor, as CPU speed will always be 
> set to the lowest possible (so there is not enough power to 
> crypt/decrypt data).
> 
> Ironically, this is the only case when starting bzip2 will speed up your 
> disk access... Or, use a userspace governor.
> 
> 
> See also http://bugzilla.kernel.org/show_bug.cgi?id=9729

I don't know about this one.
AFAIK there has been some work done there, I expect the bug in the
crypto area, not in cpufreq/ondemand layer.

A Xeon processor stepped down from 2800 to 350 looks bogus (maybe the
new ones even can, not sure), could it be that you are using
p4-clockmode driver which is doing throttling, not frequency scaling,
better try with acpi-cpufreq then.


   Thomas