# P4-clockmod vs. Intel Speedstep

## rmh3093

Has anyone with a P4 based cpu tried out the P4-clockmod cpufreq driver???

I just tried it today on my 2.0GHz P4M, with the standard Intel Speedstep driver I have only 2 available frequencies

1200000 2000000

with the P4-Clockmod I have 8

250000 500000 750000 1000000 1250000 1500000 1750000 2000000

With a slower clockspeed, less power is consumed by the processor so battery life should increase.

However at a lower clockspeed, a task may take longer time to complete, decreasing battery life.

I am going to set up a factorial experiment this week to find an optimum frequency to operate while on

battery power or even better, a range of frequencies for the ondemand governor.

Idling at 250MHz would definately be better than 1.2 or 2.0 GHz, i cant wait to see what the results will be.

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## Hibbelharry

i always used the speedstep-ich driver for my intel mobile p4 driven notebook and just stumbled over the p4-clockmod driver, too. will also set up a experiment on my notebook this week. what are your results so far ?

greetz

hibbelharry

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## sunder

I ran into this as well but I'm not ambitious enough to run experiments.  The p4-clockmod driver warns me to switch to speedstep-ich because it has voltage scaling supprt.  But will this offset the 600% increase in minimum clockspeed?  I have my laptop down to 200 Mhz with p4-clockmod and the best it can do with speedstep-ich is 1200Mhz.  The processor is a 1600Mhz  P4-M.

Could someone please tell me how to get speedstep-ich or acpi p-states to drop to a reasonable minimum clock rate?

Thanks

EDIT:

I forgot to say that I'm using the ondemand CPU frequency governer.  It's very good about scaling things back without the need for a userspace daemon, but the problem lies in the available frequencies for the 3 drivers (p4-clockmod, acpi pstates, speedstep-ich).  p4-clockmod offers the lowest scaleable frequency, but the other two offer voltage scaling.  I'm trying to get the best of both worlds.

EDIT2:

This link helped me out.  Now switching to speedstep-ich

http://www.ussg.iu.edu/hypermail/linux/kernel/0407.3/0154.html

Here's the info:

 *Quote:*   

> p4-clockmod is not really a cpufreq driver: it does not change the
> 
> frequency. The only function is to have 'idle-cycles' to cool down the
> 
> processor during intensive CPU programs: this is what the processor
> ...

 

I wish the kernel configuration help option said something along these lines.  Oh well, hope this helps someone outLast edited by sunder on Sun May 29, 2005 3:48 pm; edited 2 times in total

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## Corpse2

I'm not completely sure, but I don't think those 2 things do the same.

Speedstep is scaling your frequency and voltage down to reduce power consumption. Cpufreq only puts idle cycles between the instructions to scale down the effective frequency but in reality remains at full speed, without any changes in voltages. This way your processor does not work as hard and does not consume as much power because he's not doing anything.

I think if you put it on 1200MHz with speedstep, it will consume less compared to 1250MHz with cpufreq, but lower values with cpufreq might be better than the speedstep configuration, although your speed will be worse so performance as well.

I used cpufreq on my P4 northwood notebook and this is very usefull, I wish someone created something like this for windows...

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## brodo

 *sunder wrote:*   

> I ran into this as well but I'm not ambitious enough to run experiments.  The p4-clockmod driver warns me to switch to speedstep-ich because it has voltage scaling supprt.  But will this offset the 600% increase in minimum clockspeed?

 

Yes. p4-clockmod won't save you anything under normal usage, as the idle mode the CPU enters is equivalent to the state the CPU is put into during clock modulation. frequency and voltage scaling is what you (normally) want, so please please use speedstep-ich.

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## lamekain

Just switched to p4-clockmod from speedstep, but because of this thread I think I'll switch back.. Can anyone tell me why speedstep will only use two steps on my centrino pentium? The processor supports more...

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## brodo

 *lamekain wrote:*   

> Just switched to p4-clockmod from speedstep, but because of this thread I think I'll switch back.. Can anyone tell me why speedstep will only use two steps on my centrino pentium? The processor supports more...

 

Probably because your notebook's BIOS is broken...

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## lamekain

 *brodo wrote:*   

>  *lamekain wrote:*   Just switched to p4-clockmod from speedstep, but because of this thread I think I'll switch back.. Can anyone tell me why speedstep will only use two steps on my centrino pentium? The processor supports more... 
> 
> Probably because your notebook's BIOS is broken...

 

No, I don't think so. I have a friend that has the same processor on a thinkpad and his getting only 600 and 1500 too. But it's not really a problem. Two is already enough   :Cool: 

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