Fan control for PowerMac7_3 (#3)

H. Peter Anvin hpa at
Sat Oct 16 15:32:07 EST 2004

Benjamin Herrenschmidt wrote:
> On Sat, 2004-10-16 at 14:58, H. Peter Anvin wrote:
>>I don't know how to tell; it's a significant sound.  Let me see if I can 
>>figure it out.
> If the dual 2.5Ghz is like the old dual 2Ghz, you can run prefectly well
> with the case open, as long as you keep the plexiglass in place, which
> drives the air flow, and you'll be able to see the CPU and slots fans.
> You can also read the speed values from /sys/devices/temperature
>>OS X doesn't sound like this.  The oscillation period for what it's 
>>worth is 10 seconds.
> Ok, there must be something wrong then...

It's the backside fan that oscillates; backside_fan_pwm varies between 
30 and 100 in what is pretty much a squarewave.  See attached graph (and 
note how the other fans vary with workload.)

I probably need to write a "power virus" program for the G5 to really 
test out the high end (a power virus is a program which keeps the chip 
running as hard as it can; generally keep all pipelines stuffed.)

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