hwpmc & sampling

Niklas Sorensson nik at cs.chalmers.se
Tue Sep 27 16:24:47 PDT 2005


Hello,

I just started looking into the hwpmc support, but I am having trouble
running pmcstat in sampling mode. Here's an example of the symptoms:


nik> time pmcstat -P instructions -O samples.out ./minisat_static
~/work/benchmarks/sat/standard_mix/f2clk_30.shuffled.cnf > /dev/null

real    0m24.728s
user    0m0.001s
sys     0m0.004s

nik> pmcstat -R samples.out | grep sample | wc -l
     289


I would expect quite a lot more samples for a program that runs for
more than 20 seconds. Am I doing something wrong, or does this mean
that there is something wrong with sampling? Just counting seems to
work as expected, although I have not tested very much so far.

I am running on a current (i386) from a couple of days ago on an
amd64 machine.

Btw, I needed to add apic to my kernel config for hwpmc to. I guess
this should be documented somewhere?

/Niklas




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