Weird fan behaviour on a 2950

Tony van Lingen tony.vanlingen at epa.qld.gov.au
Mon Jun 11 22:26:26 CDT 2007


Dirkjan,

Dirkjan Bussink wrote:
> Tony van Lingen wrote:
>   
>> DirkJan,
>>     
>
> <offtopic>
> Dutch or from recent Dutch heritage? Because my name is without the
> second capital and only people with some sort of Dutch background would
> probably type it this way ;).
> </offtopic>
>
>   
Soot! Caught me out there... but I did make sure this time :)
>> I don't think its purely cosmetic. Raghavendra says:
>>     
>
> Well, the way I read it, they don't have absolute sensors anymore, but
> relative ones. I've looked at the current values and they are very
> reasonable (so the negative temperature shows a realistic temperature
> given the overheating point and the temperatures in the data center).
> Also if there is no CPU present in a socket, it shows a totally
> different value (always 50 as the temperature, tested on various
> machines), indicating it does read something from the CPU.
>
> I've also find no reason behind the fact that the bit is set. It could
> be only because it is confusing, or because the data actually doesn't
> make any sense (in which case it would be very coincidental that the
> temperatures actually look like reasonable values). 
Reading the info in Roger While's link, that would make perfect sense (

Roger While said:
> This may or may not be helpful -
> http://softwarecommunity.intel.com/isn/Community/en-US/forums/3/30222546/ShowThread.aspx
>
>   
)

Without the CPU there's nothing to read, so it will return some default 
value. Judging by the thread above, the 50 value (wich is an offset, not 
temperature) would mean "boiling hot" - a safe default.

With the CPU present it would read out the IA32_TEMPERATURE_TARGET MSR, 
but the value would not have any documented meaning. Thus the solution 
to hide this reading is perfectly reasonable and not solely cosmetic - 
it could indeed give the impression that your system is OK when it's in 
fact not. To make it meaningful apparently you need to know a value for 
the PROCHOT assertion, which cannot be read and is implementation 
dependent. The hardware can still use it (for throttling fans), so it 
still makes sense for the bit to be set.
(my interpretation)

Tony van Lingen
Systems Administrator and DBA



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