Does any part / packages in the Ubuntu 12.04 OS use the performance monitor counters (PMC) in the CPU?

[Qichang Liang]

I plan to run some experiments on a multicore machine that has four
16-core CPUs from the 15h family, with Ubuntu 12.04 installed.

My experiment requires the use of performance monitor counters (PMC).
However when I did some test readings on the PMC (two immediate
consecutive reads of the PMC, without doing anything in between.  The
results look funny, as sometimes the reading decreases, or increase
wildly.

This does not happen if I revert to the 10.04 installation with the
stock 10.04 kernel, or 10.04 installation with a linux-3.2 vanilla
kernel.

it looks to me that some parts in the Ubuntu-12.04 also use the PMC
counters, and therefore we have a contention on the counters.  Could
anyone confirm whether any packages / software included in the 12.04
OS could have also used the PMC counteres?  If so, I need to disable
these software, before performance my experiments.

Thanks!

Qichang