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SubjectRe: 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@it-loops.com> 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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