AMD Athlon64 cool'n quiet - questions

[Jonathan Berry]

On Mon, 21 Mar 2005 15:40:02 +0100, Alexander Volovics <awol at home.nl> wrote:
> On Mon, Mar 21, 2005 at 01:19:43PM +0000, James Wilkinson wrote:
> > Alexander Volovics wrote:
> > > However I have only ever seen 2 freqencies in use: 1000 and 2200.
> > > This could because 1800/2000 are excluded from use somewhere or
> > > because they are 'transient states', only used when switching from
> > > 1000 to 2200.
[snip]
> 
> Yes, this does demonstrate it nicely. In my case I saw both intermediate
> speeds reported a few times before it settled down to a stable 1000 again.
> 
> But this indeed seems to indicate that these are only 'stepping stones'
> between 1000 and 2200. Can they be exploited in some useful way, and how?
> (that is except for setting a max/min cpuspeed smaller/larger
>  than the actual max/min, which I suppose you can do).

Whether and how these intermediate frequencies are used depends upon
the algorithm used by cpuspeed and the CPU usage.  I use powernowd to
do my frequency scaling, and it supports several different algorithms.
 There is also some good info on these sites about the frequency
scaling concept:
http://www.deater.net/john/powernowd.html
http://n-dimensional.de/projects/cpufreq/algorithms.txt
I will occasionally see my processor hang around on the intermediate
frequency (it can do 0.8 1.6 and 2.0 GHz), but most of the time it is
either not busy or really busy and so tend to use the lowest and
highest most.

> > I don't know about you, but most of my computer usage tends to be things
> > like surfing the web, writing e-mails, or listening to music. That's
> > stuff you can do perfectly well on a 500 MHz computer. You don't need
> > more than 1 GHz of Athlon 64 power, so the system keeps clock speed down
> > to 1 GHz.
> 
> In my case mostly too. But I still have some activities where I can
> exploit the full power.

Right, that is what the scaler is for. It should crank up the
frequency when you do something that uses a lot of CPU.  Most of the
time, the CPU isn't doing much useful work because it is waiting for
you to do something.  It really doesn't matter how fast it can execute
NOP commands : ) so it scales back.  This keeps the CPU cooler and
(for a laptop) uses less energy.  Then when you want to do something,
like compile a program, it increases the frequency get the speed and
performance you paid for.

> Thanks for the 'demonstration'.

The cpufreq applet is really cool to be able to see what speed your
CPU is running at.

> Alexander

Jonathan