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Date: Wed, 28 Sep 2005 15:22:14 +0530
From: Joseph Koshy <joseph.koshy@gmail.com>
To: Niklas Sorensson <nik@cs.chalmers.se>
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Cc: freebsd-current@freebsd.org
Subject: Re: hwpmc & sampling
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Niklas,

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.

--
FreeBSD Volunteer,     http://people.freebsd.org/~jkoshy