Detecting CPU throttling on over temperature

Alexander Motin mav at
Wed Sep 9 04:21:43 UTC 2009

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.

> The problem is that the CPU temperature is only a proxy measurement, I 
> would much prefer to be told directly the BIOS is throttling rather 
> than guess :)

While ACPI could implement thermal throttling, AFAIK TM1/TM2
technologies of P4 and above families are working just in CPU hardware.
BIOS only initializes them.

Alexander Motin

More information about the freebsd-stable mailing list