Detecting CPU throttling on over temperature

Alexander Motin mav at
Wed Sep 9 13:16:17 UTC 2009

Robert Noland wrote:
> On Wed, 2009-09-09 at 17:47 +0930, Daniel O'Connor wrote:
>> On Wed, 9 Sep 2009, Alexander Motin wrote:
>>> Daniel O'Connor wrote:
>>>> On Wed, 9 Sep 2009, Alexander Motin wrote:
>>>>> Daniel O'Connor wrote:
>>>>>> I recently discovered a system where the floppy drive cable was
>>>>>> intermittently fouling the CPU fan - I believe this caused the
>>>>>> CPU to overheat and then get throttled by the BIOS.
>>>>>> Does anyone know if it is possible to determine if this is the
>>>>>> case? ie is there a way to be informed if throttling has
>>>>>> occurred?
>>>>> Theoretically it is possible. I know off-topic tool reporting
>>>>> this. Also you can just monitor CPU temperature, depending on CPU
>>>>> type.
>>>> Monitoring CPU temperature is a bit difficult, there are a lack of
>>>> tools (although I have some code it's not complete).
>>> There indeed problems with MB monitoring, as it is non-standard. But
>>> modern CPUs also include on-chip thermal sensors. For Core2Duo family
>>> coretemp module works fine and precisely.
>> Ahh coretemp, I had forgotten about that.
>> I did a test on the bench (on a 7.2 system) here and realised that I 
>> can't actually detect throttling. coretemp reported 72 & 78C but the 
>> frequency was still 2933MHz.
>> I am pretty sure it would be throttling but I think that works by 
>> maintaining the frequency but stalling the CPU some percentage of the 
>> time. I have p4tcc loaded (in GENERIC) but it doesn't show up, I only 
>> get..
> Is this a core2duo?  IIRC, they generally don't go into TCC until around
> 100C.  I did pull the c2d cpu docs at one point trying to look at
> cpufreq.  If you are bored, you can grab the docs from intel and double
> check.

AFAIR C2D supports three protection technologies. When CPU is hot, it
starts reducing frequency (multiplier) and voltage, alike to IEST. If it
is insufficient, it starts to skip core cycles, alike to TCC. If it is
still insufficient and temperature rises above about 100C, emergency
shutdown happens.

Alexander Motin

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