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OS X 10.5.3 (and beyond) Increases CPU Power Draw?

J

jsurpless

macrumors member
Original poster
Aug 6, 2009
88
0
Hi all

I've got another ongoing thread (2006 Mac Pro Elevated CPU Temps) where I've been attempting to determine why my 2006 Mac Pro was running so much warmer than I recall at time of purchase...

By sheer luck, I seem to have stumbled on the cause... when I first noticed it, I was running 10.5.7 with the CPUs idling around 130F or so... as noted in that thread, I tried all sorts of things such as cleaning the dust out, reapplying the thermal paste, etc... all of which had no impact... for an unrelated issue, I decided to re-install OS X 10.5 base version and I was shocked to discover my CPU temps back down in the mid-90s F or so...

I happened to have taken some screenshots of Hardware Monitor and was able to compare them against the current readings... under OS X 10.5 -> 10.5.2, each CPU draws ~10W @ idle; under 10.5.3 and beyond, the CPU draw increases to ~30W @ idle. Naturally, this extreme increase results in the aforementioned temperature increase... I'm not sure as to the cause but my immediate suspicion is that some low-power CPU mode is disabled in the later revisions...

I've spoken to Apple about this and they're looking into it but in the mean time, I was wondering if anyone has any input on this?

-Justin
 
jsurpless said:
Hi all

I've got another ongoing thread (2006 Mac Pro Elevated CPU Temps) where I've been attempting to determine why my 2006 Mac Pro was running so much warmer than I recall at time of purchase...

By sheer luck, I seem to have stumbled on the cause... when I first noticed it, I was running 10.5.7 with the CPUs idling around 130F or so... as noted in that thread, I tried all sorts of things such as cleaning the dust out, reapplying the thermal paste, etc... all of which had no impact... for an unrelated issue, I decided to re-install OS X 10.5 base version and I was shocked to discover my CPU temps back down in the mid-90s F or so...

I happened to have taken some screenshots of Hardware Monitor and was able to compare them against the current readings... under OS X 10.5 -> 10.5.2, each CPU draws ~10W @ idle; under 10.5.3 and beyond, the CPU draw increases to ~30W @ idle. Naturally, this extreme increase results in the aforementioned temperature increase... I'm not sure as to the cause but my immediate suspicion is that some low-power CPU mode is disabled in the later revisions...

I've spoken to Apple about this and they're looking into it but in the mean time, I was wondering if anyone has any input on this?

-Justin
Click to expand...

Is that something to do with SpeedStep?
 
Speedstep is a technology where the CPU steps down the internal voltage and frequency when it senses idle.

http://en.wikipedia.org/wiki/SpeedStep

Mac OS also has SpeedStep built into the kernel, since the release of the Intel version of Mac OS X 10.4 and is already enabled. It cannot be controlled in the System Preference "Energy Saver." To disable this feature, and set a specific clock speed (full speed or reduced) requires a third party application, such as coolbook.
Click to expand...
 
Are others observing similar behavior? What are people seeing for power draw at idle?
 
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