Detecting CPU throttling on over temperature

[Robert Noland]

On Wed, 2009-09-09 at 16:16 +0300, Alexander Motin wrote:
> 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.

Your recollection is probably more accurate than mine.  My brain is
full, so every new doc that I read pushes something else out.

robert.

-- 
Robert Noland <rnoland at FreeBSD.org>
FreeBSD