hwpmc & sampling

Joseph Koshy joseph.koshy at gmail.com
Wed Sep 28 02:58:55 PDT 2005


ns> time pmcstat -P instructions -O samples.out ./minisat_static

ns> I would expect quite a lot more samples for a program that
ns> runs for more than 20 seconds. Am I doing something wrong,

Could you check whether the output of "pmccontrol -s", shows the
'interrupts dropped due to lack of space' count as non-zero?

If it is, you will need to increase the tunable "kern.hwpmc.nsamples"
till you get clean runs.

I guess I should make pmcstat check and warn the user about
sampling stalls encountered.

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

It seems to be needed on the i386, but not on the amd64.  Will fix.

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