Underclocking and Undervolting a MP 2008 2.8 x 8

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[ildondeigiocchi]

Didnt want to hijack handheldgames' thread - https://forums.macrumors.com/threads/795966/... so thought i'd post this separately.

There's an interesting post on there from lbodnar - https://forums.macrumors.com/threads/795966/... Post 602 - which basically gives the terminal command to both underclock and undervolt the CPU(s) on a MP 2009.

Like many I'm aware of the overclocking app from last year, (German site I think) but wasn't aware how easy it is potentially to go the other way.

lbodnar replied to me later (Post 613), confirming it's possible on a MP 2008 2.8x8 as well as others, but when i try either of the 2 commands he lists (cribbed his post below), I get - 'unknown processor type' back in Terminal.

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For those who have kernel panic on high CPU load - have you tried reducing CPU voltage a little bit?

If you have CHUD Tools installed try running
Code:

reggie_se -r -n IA32_PERF_CTL -i a

this will tell you your current PLL multiplier and core voltage settings. Try dropping voltage a few notches down and see if this helps. The command to do that is
Code:

sudo reggie_se -w 0x91E -n IA32_PERF_CTL -i a

here 9 is PLL multiplier (CPU core speed) and 1E is core voltage (dropped from 26.) These values are hexadecimal and relate to 3.0GHz X5365 Xeon. W35xx will have different multiplier and voltage but the idea is the same. Let us know if this helps. If you drop voltage too much you will start getting kernel panic again.

This will reset back after restart or wake-up from sleep.
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I'm pretty sure i have CHUD Tools installed from way back - have CHUD Remover amongst other apps/files in the Developer/Applications/Performance Tools/CHUD folder.

I'd like to try this and have it available for those times when i leave the MP running for a weekend or longer unattended. No real need for it to be running at max capability for the full 72 + hours.

Anyone (lbodnar?) able to help out with specific CPU variants and the values that will set useful CPU Clock and Voltage values?

I wouldn't play with such things. A minor mistake could lead into a huge problem. Better safe than sorry is what the old proverb says.

 

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[lbodnar]

Can you run reggie_se -l (this is lower case "L") to list all processor MSR registers?

This should be pretty safe because you cannot exceed neither CPU speed nor its voltage.

Could you please also run

sysctl -a | grep cpu

to get exact CPU details?

 

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[Cindori]

aren't you thinking the wrong way? crashes usually come when you have to little volt. if you have too much volt, your cpu will overheat. i'm sure your mac pro is not doing that since they run very cool.

 

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