linux-kernel - RE: [PATCH] perf tools: ignore zombie process for user profile

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Date:   Wed, 14 Dec 2016 18:26:02 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     "acme@...nel.org" <acme@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "andi@...stfloor.org" <andi@...stfloor.org>
Subject: RE: [PATCH] perf tools: ignore zombie process for user profile



> 
> On Wed, Dec 14, 2016 at 12:48:05PM -0500, kan.liang@...el.com wrote:
> > From: Kan Liang <kan.liang@...el.com>
> >
> > If user has zombie process, the perf record -u will error out.
> > Here is an example.
> >  $ ./testd &
> >  [1] 23796
> >  $ sudo perf record -e cycles -u kan
> >  Error:
> >  The sys_perf_event_open() syscall returned with 3 (No such process)
> > for  event (cycles).
> >  /bin/dmesg may provide additional information.
> >  No CONFIG_PERF_EVENTS=y kernel support configured?
> >
> > The source code of testd is as below.
> >  int main() {
> >
> > 	if (fork())
> > 	{
> > 		while (1);
> > 	}
> > 	return 0;
> >  }
> >
> > Zombie process is dead process. It is meaningless to profile it.
> > It's better to ignore it for user profile.
> 
> I recently posted different patch for same issue:
>   http://marc.info/?l=linux-kernel&m=148153895827359&w=2

The change as below make me confuse.
+	/* The system wide setup does not work with threads. */
+	if (!evsel->system_wide)
+		return false;
It looks the meaning of the comments is inconsistent with the code.


Your original patch doesn't work well with the issue.
But if I change the above code as below, the issue is fixed.
	if (evsel->system_wide)
		return false;

Thanks,
Kan