[Beowulf] bizarre scaling behavior on a Nehalem

Craig Tierney Craig.Tierney at noaa.gov
Wed Aug 12 14:06:23 EDT 2009


Rahul Nabar wrote:
> On Wed, Aug 12, 2009 at 11:32 AM, Craig Tierney<Craig.Tierney at noaa.gov> wrote:
>> What do you mean normally?  I am running Centos 5.3 with 2.6.18-128.2.1
>> right now on a 448 node Nehalem cluster.  I am so far happy with how things work.
>> The original Centos 5.3 kernel, 2.6.18-128.1.10 had bugs in Nelahem support
>> where nodes would just start randomly run slow.  Upgrading the kernel
>> fixed that.  But that performance problem was either all or none, I don't recall
>> it exhibiting itself in the way that Rahul described.
>>
> 
> I was trying another angle. Playing with the power profiles. Just
> downloaded cpufreq-utils via yum. Tried to see what profile was
> loaded:
> 
> cpufreq-info
> cpufrequtils 005: cpufreq-info (C) Dominik Brodowski 2004-2006
> Report errors and bugs to cpufreq at vger.kernel.org, please.
> analyzing CPU 0:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 1:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 2:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 3:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 4:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 5:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 6:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 7:
>   no or unknown cpufreq driver is active on this CPU
> 
> Is this lack of the right drivers indicative of a deeper fault or is
> this fairly local to this issue? This could be a clue or a red
> herring. Just thought that I ought to post it.
> 

I read there are several different tools to manage the CPU frequency.
If you are using Centos/Redhat try:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

Does it list any?  If not, that might be why cpufreq-info can't
find anything.

Craig



-- 
Craig Tierney (craig.tierney at noaa.gov)
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