Linux users of Sony Z1 series

[Mark Taylor <>]

On Sun, 2004-07-18 at 08:34, Nils Spengler wrote:
> > cpufreqd?
> 
> I think it was speedfreq but i dont quite remember.
> 
> > BTW: talking of CPU frequencies: What is the lowest cpu speed you can
> > get out of your Z1 with Linux? I don't get it below 600MHz (which is 
> > according to the docs in the speedstep-centrino kernel-driver where a
> > Intel Datasheet is referenced the official lower limit for the
> > processor if I've read it correctly) But when running WinXP on the
> > laptop and having there the speedstepping activated and look at the
> > System properties, Windows tells me that the processor is running at
> > something about 280MHz... duh?!?... Perhaps the MHz counter is buggy
> > which I doubt -- also because Windows tells me a remaining battery
> > runtime of 5-6h (which is then really possible). 
> >
> > Perhaps there are some other things involved to throttle the CPU even
> > slower than the 600MHz. If anyone has similar experience or know where
> > to look for...
> 
> I think i can explain that but i'm not quite sure.
> Theoretically you can Step lower than 600mhz. But the interesting things are
> the speed Steps. They differ in power consumption. To use a lower frequency
> does not automatically save power if it is in the same range of one speed
> Step. What i mean is, it doesnt make sense to go lower than 600mhz cause it
> takes the same power if you are on 300 or on 600 mhz. So windows uses every
> possible frequency, linux only uses the speed Steps.
> 

This sounds like ACPI's throttling?  which we can set it & read the
current value via /proc/acpi/processor/CPU0/throttling.  

I spend some time trying to find information on how throttling works
with cpu frequency, and if there was any advantage to using both.  I
never found anything, but I did run this test:

idle system, screen off, 600MHz
with no throttling: power consumption reported by ACPI:  9851 mw
with 87% throttling:  power consumption reported by ACPI:  9825 mw

So my conclusion was that throttling was not worth the trouble if you
have already steped down to 600MHz - you cant save any more power.  This
seems to agree with what Nils is saying.  

Someone did tell me that on a loaded system, throttling would save
power, but on a loaded system I would want throttling turned off and the
frequency increased.

Mark