linux-kernel - Re: [PATCH 4/5] perf tools: Allow to ignore missing pid

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Date:   Mon, 12 Dec 2016 15:53:12 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, David Ahern <dsahern@...il.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 4/5] perf tools: Allow to ignore missing pid

On Mon, Dec 12, 2016 at 11:32:09AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Dec 12, 2016 at 11:35:42AM +0100, Jiri Olsa escreveu:
> > Adding perf_evsel::ignore_missing_cpu_thread bool.
> > 
> > When set true, it allows perf to ignore error of missing
> > pid of perf event syscall.
> > 
> > We remove missing thread id from the thread_map, so the
> > rest of the processing like ioctl and mmap won't get
> > disturbed with -1 fd
> 
> What was the test performed? I tried it here the following while doing
> a 'make -j4 allmodconfig' in the background, i.e. tons of threads coming
> and going, and I sometimes get:
> 
> [root@...et ~]# perf record -u acme 
> Error:
> The sys_perf_event_open() syscall returned with 3 (No such process) for
> event (cycles:ppp).
> /bin/dmesg may provide additional information.
> No CONFIG_PERF_EVENTS=y kernel support configured?

I dont think it's fast enough (start/stop) to hit the race, I've got best
results with having on background this:

  while :; do /usr/bin/true; done

jirka