linux-kernel - Re: [PATCH] perf tools: Fix ppid for non-main thread

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Date:	Thu, 9 Apr 2015 13:05:19 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	David Ahern <david.ahern@...cle.com>
Cc:	acme@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Fix ppid for non-main thread

On Thu, Apr 09, 2015 at 12:48:27PM -0400, David Ahern wrote:
> Commit ca6c41c59b9 sets the ppid based on what is read from the
> /proc/pid/status file when synthesizing fork events. This is correct
> thing to do for new processes but not threads of a process. Fix
> ppid for threads to be the main thread when synthesizing fork events
> (ie., assume main thread spawned all sub-threads in a process).

That sounds right. :-)  Sorry I should have noticed that a couple of weeks
ago.

Acked-by: Don Zickus <dzickus@...hat.com>

> 
> Reported-by: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> Signed-off-by: David Ahern <david.ahern@...cle.com>
> Cc: Don Zickus <dzickus@...hat.com>
> ---
>  tools/perf/util/event.c |   14 ++++++++++++--
>  1 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index 186929a..ff866c4 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -183,8 +183,18 @@ static int perf_event__synthesize_fork(struct perf_tool *tool,
>  {
>  	memset(&event->fork, 0, sizeof(event->fork) + machine->id_hdr_size);
>  
> -	event->fork.ppid = ppid;
> -	event->fork.ptid = ppid;
> +	/*
> +	 * for main thread set parent to ppid from status file. For other
> +	 * threads set parent pid to main thread. ie., assume main thread
> +	 * spawns all threads in a process
> +	*/
> +	if (tgid == pid) {
> +		event->fork.ppid = ppid;
> +		event->fork.ptid = ppid;
> +	} else {
> +		event->fork.ppid = tgid;
> +		event->fork.ptid = tgid;
> +	}
>  	event->fork.pid  = tgid;
>  	event->fork.tid  = pid;
>  	event->fork.header.type = PERF_RECORD_FORK;
> -- 
> 1.7.1
> 
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