cpu frequencies

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rossmoore
Posts: 1
Joined: Tue 26. May 2009, 11:55

cpu frequencies

Post by rossmoore » Thu 28. May 2009, 04:53

Hi,

I've just starting trying to use PHC. I've installed a patched kernel (I'm on Jaunty), and have a script which sets the CPU frequencies then tries different voltages while stressing the CPU to ensure stability.

There's a problem though. While burnMMX is running to stress the CPU, the temperature rises. As the temperature approaches 98C, the CPU frequency is scaled down to stop damage to the CPU even though the governor is in userspace. Very sensible of some part of linux / the bios to protect my CPU. But now I'm not running the right frequency, so my test of stability for a particular voltage is out the window... And even worse, the script is continuing to try different voltages.

Do you have any advice for me? I can think of a couple of things I could do now:
1. Find whatever it is that's trying to protect my CPU and kill it - but that could get expensive if my CPU does blow.
2. Alter the script so that after each 20 second burnMMX test it pauses for 1 minute to let everything cool down.

Anything else? Do others not run in to this problem?

Yours,
Ross

the-fallen
Administrator
Posts: 346
Joined: Wed 9. Jul 2008, 19:57

Re: cpu frequencies

Post by the-fallen » Thu 28. May 2009, 16:31

Heya rossmoore,

first: welcome on board.

This emergency throttling of clock frequency you described is build-in to modern CPUs so CPU vendors do not need to trust any third-party software.

Everything you described then I did not really understand.
What script do you run? What CPU do you have? What you mean with "I'm not running the right frequency"?

For your two questions:
1:
You can not (end even if, you should not) disengage the protection of your CPU (else you would get some magical smoke from your CPU :) )

2:
I do not know what script you use but since I never created one to stress-test CPUs. I can only give you the hint to do the stress test manually (there were some reasons I never wrote a stress-test script).
To do this you simply set a fixed frequency, run cpuburn or mprime or whatever-you-wish to fire up the CPU load and then lower VIDs step-by-step until the stress-test crashes. Give your system enough time for each VID you try (one minute is a good value) to be sure the CPU is working stable with the VID.

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