Re: cpufreq: powernow-k8 frequency transitions question

[Nebojsa Trpkovic <trxman@gmail.com>]

The most usefull powersaving is achieved by lowering the voltage and not 
the further lowering of frequency.
Power consumption (and heat dissipation) rise almost exactly with the 
square of core voltage, so one could save a lot of power by lowering 
voltage even just a little bit.
 I've found that almost all Athlon64 CPUs can work at a lot lower 
voltage then in AMD specs.

Newcastle 3000+   p-states: 1.0GHz @1.1V, 1.8GHz @1.4V, 2.0GHz @1.5V
http://www.aaen.edu.yu/~tnt/newcastle.png

Winchester 3000+   p-states: 1.0GHz @1.1V, 1.8GHz @1.4V
http://www.aaen.edu.yu/~tnt/winchester.png

So, I've modified powernow-k8.c to lower the voltages read from BIOS for 
every p-state. Although I've made graphs of stable voltages by running 
prime95 for at least 12 hours in every state,  I've left 0.1V over the 
minimum stable voltage just to be 110% sure it will work stable:
Winchester runs with 1.0GHz @1.0V and 1.8GHz @1.275V

Winchester is turned on 24/7 for last 6 months as it serves one LAN and 
one wifi network (DNS, Proxy, firewall, web, teamspeak2, gentoo rsync, 
ftp, 1TB samba...) and it has NO problems at all!

Newcastle was my desktop CPU and now there's Palermo Sempron 2800+.

Greetings,
Nebojsa Trpkovic



Gunter Ohrner wrote:

>Bruno Ducrot wrote:
>  
>
>>I'm wondering if this would have some more power saving if there are more
>>low p-states.  I should some day look at this more seriously.
>>    
>>
>
>I own a Winchester 3000+ (max. 1,8GHz) which I tried to operate at 800 MHz
>(instead of 1,0GHz) but it locked hard. It can be forced to intermediate
>out-of-spec speeds (1,2GHz, 1,4GHz and 1,6GHz, although 1,4 should not be
>reachable according to AMDs frequency transition spec).
>
>Though I'm not sure if there's any win from these unsupported P-states as
>1,0GHz should suffice for most tasks and for everything else the system can
>quickly toggle to 1,8 GHz. I currently can't think of any task which would
>require more processing power than provided by 1,0GHz but less than
>provided by 1,8GHz over a longer period of time, so that the intermediate
>P-states would actually be used by the ondemand governor for longer than a
>fraction of a second... Though it could be interesting for faster CPUs than
>mine that are decoding HD video or similar.
>
>Greetings,
>
>  Gunter
>
>  
>