From: David Ahern <dsahern@gmail.com>
To: Don Zickus <dzickus@redhat.com>
Cc: acme@kernel.org, linux-kernel@vger.kernel.org,
Joe Mario <jmario@redhat.com>, Jiri Olsa <jolsa@redhat.com>
Subject: Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events
Date: Thu, 26 Mar 2015 15:37:29 -0600 [thread overview]
Message-ID: <55147C19.5090302@gmail.com> (raw)
In-Reply-To: <20150326211146.GZ162412@redhat.com>
On 3/26/15 3:11 PM, Don Zickus wrote:
> Sorry for drawing this out. Originally the performance still seemed off.
> But as we split the patch up to see where the perf impact was, the problem
> seemed to have disappeared. So we are testing the original patch again.
>
> The only difference now is we were playing with the -BN option in perf based
> on your changelog, just because we never used it before. :-)
I was beyond surprised that you were measuring a 50% hit with the first
patch. As mentioned in a previous response it only adds the processing
of 3 additional lines to the already opened and read /proc/pid/status
file. So, when I wrote this second version I wanted to make sure we are
only measuring the impact of this change. The /proc/pid/status files are
read on startup of the record -- before any samples are taken.
The intent of '-e cpu-clock -F 1000 -- usleep 1' is to avoid any samples
since we don't care about them. Really the -a should be dropped as well
-- no need to open per-cpu events.
-B impacts processing done at the end of the run:
builin-record.c, __cmd_record():
if (!rec->no_buildid)
process_buildids(rec);
and -N says don't copying anything to ~/.debug. All together it tries to
focus the measurement to /proc walking.
>
> One last test without the -BN option and if that looks fine, then we have no
> objections. Again sorry for dragging this out. I will let you know
> tomorrow EST.
no problem; appreciate the heads up.
next prev parent reply other threads:[~2015-03-26 21:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-25 16:51 [PATCH v2] perf tool: Fix ppid for synthesized fork events David Ahern
2015-03-25 19:15 ` Don Zickus
2015-03-25 19:55 ` David Ahern
2015-03-25 20:26 ` Don Zickus
2015-03-26 21:11 ` Don Zickus
2015-03-26 21:37 ` David Ahern [this message]
2015-03-27 13:10 ` Don Zickus
2015-03-27 14:03 ` David Ahern
2015-03-27 14:20 ` Arnaldo Carvalho de Melo
2015-03-27 19:49 ` Don Zickus
2015-03-27 20:09 ` Arnaldo Carvalho de Melo
2015-03-27 20:10 ` David Ahern
2015-03-27 20:25 ` Don Zickus
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