kern/179827: [hwpmc] process-mode counters aren't correctly read on multi-core machines

[Adrian Chadd]

The following reply was made to PR kern/179827; it has been noted by GNATS.

From: Adrian Chadd <adrian at freebsd.org>
To: hiren panchasara <hiren.panchasara at gmail.com>
Cc: bug-followup at freebsd.org
Subject: Re: kern/179827: [hwpmc] process-mode counters aren't correctly
 read on multi-core machines
Date: Sat, 22 Jun 2013 13:23:24 -0700

 Right. Do that but with the test running in another window, so you
 don't get the message overlap.
 
 THen look at how the results show lots of '0' from pmcstat, and then
 correlate that with the one-second "PMC,OPS" sample lines. See how
 whenever they're run whilst the process is running (ie, the last event
 was SWI) and it hasn't yet been de-scheduled. because it's still
 running, the saved counter is never updated with the PMC counter and
 subsequent reads (until it does get de-scheduled!) return the same
 cached value. Hence, lots of '0's, followed by a big, big counter
 value.
 
 
 
 
 adrian