Re: 2.6.25.x: Wrong CPU frequency (cpufreq table) with p4-clockmod

Arjan van de Ven wrote:
On Sun, 1 Jun 2008 23:57:14 +0200
Guntsche Michael <mike@xxxxxxxxxxxx> wrote:

On May 30, 2008, at 16:07, Guntsche Michael wrote:

I am most interested in keeping the temperature of my CPU down, which means slower fans, which means less noise.
The main "problem" I have is that I do not know if this is a
simple display issue or if I am having a more fundamental problem
here.
Just FYI I found out the cause of my problem.

Reverting
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=ed9cbcd40004904dbe61ccc16d6106a7de38c998
this patch resultsin the correct numbers for me.

<cpuinfo snip>
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 1
model name : Intel(R) Pentium(R) 4 CPU 1.70GHz
stepping : 2
cpu MHz : 637.500
<snip>

This patch was reverted because other people seem to have problems with it, reverting the revert does not look like a good idea either.
But since I know now, that this is just a "display" problem and everything is working otherwise, I'll just patch this locally for my machine here.


just as a side note.. you do realize that with p4-clockmod, your cpu is
still running at 1.7 GHz right? (it's just doing less work '-)

From my testing, I believe the only thing that p4-clockmod does is forces an idle call when it could otherwise do work on an active process, so fullspeed and idle uses *EXACTLY* the same amount of power as p4-clockmod slower speed and idle (and therefore generates exactly the same amount of heat), the only power difference would be that if you were using p4-clockmod to slow down the cpu when it had an active running process (force the cpu to be idle a lot of the time even though it has work). Arjan's point is that if you are using p4-clockmod to slow down an idle cpu in hopes of saving power when the cpu is not being used, then it is not going to make *ANY* difference in the power usage at all.

I tried it on my p4 here, and cannot see any power difference in idle/fullspeed and idle/slowspeed, this is unlike the later power saving stuff that actually does slow down the cpu frequency, and you can measure a different amount of power usage with the different clock speeds and an idle cpu.

Roger
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