Fan control for PowerMac7_3 (#3)

H. Peter Anvin hpa at
Sat Oct 16 14:58:07 EST 2004

Benjamin Herrenschmidt wrote:
> On Sat, 2004-10-16 at 14:24, H. Peter Anvin wrote:
>>Benjamin Herrenschmidt wrote:
>>>Ok, here's a new patch that fixes a few issues, it's been
>>>tested on a non-liquid cooled system and appear to work ok.
>>I'm testing it out right now.  It is definitely suffering from some 
>>degree of oscillation when idling, and it seems to be one particular 
>>(set of) fan(s) that is having that problem.
> Which ones ? The CPU fans ?

I don't know how to tell; it's a significant sound.  Let me see if I can 
figure it out.

>>Note that one cause of oscillation at low speed is that there is a 
>>minimum speed below which the fans will simply stop.  This may be what 
>>is happening here.
> Do the fan actually stop ? Yes we "floor" the fan speeds and indeed,
> Apple algorithm is known to slowly oscillate, on my box it's between
> 300 and 1000 RPM for the CPU fans over a period of a minute or 2.
> Such an oscillation is expected. Something worse would mean we get
> something wrong. Did you compare against OS X ?

OS X doesn't sound like this.  The oscillation period for what it's 
worth is 10 seconds.


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