linux-kernel - Re: [PATCH 3/3] perf record: Synthesize COMM event for a command line workload

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Date:	Wed, 20 May 2015 09:08:35 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 3/3] perf record: Synthesize COMM event for a command
 line workload

On Wed, May 20, 2015 at 11:48:35AM +0900, Namhyung Kim wrote:
> When perf creates a new child to profile, the events are enabled on
> exec().  And in this case, it doesn't synthesize any event for the
> child since they'll be generated during exec().  But there's an window
> between the enabling and the event generation.
> 
> It used to be overcome since samples are only in kernel (so we always
> have the map) and the comm is overridden by a later COMM event.
> However it won't work if events are processed and displayed before the
> COMM event overrides like in 'perf script'.  This leads to those early
> samples (like native_write_msr_safe) not having a comm but pid (like
> ':15328').
> 
> So it needs to synthesize COMM event for the child explicitly before
> enabling so that it can have a correct comm.  But at this time, the
> comm will be "perf" since it's not exec-ed yet.
> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/builtin-record.c | 41 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 5dfe91395617..a0821ee92e27 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -469,6 +469,43 @@ static void workload_exec_failed_signal(int signo __maybe_unused,
>  	child_finished = 1;
>  }
>  
> +static int synthesize_workload_comm_event(struct perf_evlist *evlist, void *arg)
> +{
> +	union perf_event *event;
> +	struct record *rec = arg;
> +	struct machine *machine = &rec->session->machines.host;
> +	int pid = evlist->workload.pid;
> +	const char *comm_str = program_invocation_short_name;

never heard of program_invocation_short_name ;-) nice..

for the patchset:
Acked-by: Jiri Olsa <jolsa@...nel.org>

I tested the record/script use case.. works ok

thanks,
jirka
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