[Beowulf] OT: acpi-cpufreq won't load because???

mathog mathog at caltech.edu
Tue Sep 13 10:12:22 PDT 2016

On 01-Sep-2016 10:14, mathog wrote:
> Found a manual for a poweredge and the BIOS apparently has a setting
> that in one state lets the BIOS control the CPU speeds, and in the
> other lets the OS do it.  I bet it must be in the first state on those
> two Poweredges.  What does that setting do with respect to fan speed
> control though?

Just a quick note to complete this thread, in case somebody stumbles 
onto it with a search.

The BIOS was indeed in the "Active Power Control" state, in which the 
BIOS controls everything.  Changed the overall power to "custom" and the 
CPU setting to "OS Control" and then cpu_freq worked as expected.  MHz 
scale up and down correctly with load, and the CPU speed when idle is 
now only 1197, so it should use less power than before.

There are only two BIOS power settings for the fan: minimum power and 
maximum performance.  In the former the machine is very reluctant to 
increase the fan speed from 1200Hz.  Loaded 7 of the 8 threads with:

   dd if=/dev/zero of=/dev/null &

and it drove the 4 CPU temperatures up from 27C to 65C.  Let it sit 
there for a few minutes and the fan did not budge from the 1200Hz it had 
started at.  The fan can go faster, when the machine powers on the fan 
is really loud, then it slows down.  Apparently some Dell's have a fan 
setting "Maximum Air Exhaust Temperature" which limits exhaust to 50C, 
however that option isn't present on the PowerEdge T310.  The exhaust 
didn't feel nearly that hot even with the dd's running because the 
ambient is only 21C and this cool air is diluting the hot air coming off 
the processors.  Unclear at present how hot the innards of the T310 must 
get before the fan speed will increase.


David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech

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