linux-kernel - Re: perf: thread is its own parent

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Date:	Thu, 19 Mar 2015 09:20:48 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf: thread is its own parent

On Wed, Mar 18, 2015 at 05:56:33PM -0600, David Ahern wrote:
> Don:
> 
> In this commit:
> 
> commit 363b785f3805a2632eb09a8b430842461c21a640
> Author: Don Zickus <dzickus@...hat.com>
> Date:   Fri Mar 14 10:43:44 2014 -0400
> 
>     perf tools: Speed up thread map generation
> 
> you made a thread its own parent when synthesizing fork events:
> 
> static int perf_event__synthesize_fork(struct perf_tool *tool,
>                                        union perf_event *event, pid_t pid,
>                                        pid_t tgid,
> perf_event__handler_t process,
>                                        struct machine *machine)
> {
>         memset(&event->fork, 0, sizeof(event->fork) +
> machine->id_hdr_size);
> 
>         event->fork.ppid = tgid;
>         event->fork.ptid = tgid;
>         event->fork.pid  = tgid;
>         event->fork.tid  = pid;
>         event->fork.header.type = PERF_RECORD_FORK;
> 
> 
> Any particular reason or just an oversight?

Hi David,

Honestly I don't recall.   The commit log tells you the problem I was trying
to solve.  Instead of parsing text strings from /proc/maps/<pid>, I believe
it was waaaay faster to copy the thread maps.

This could have been an oversight.  I might have falsely assumed tgid ==
ppid?

Are you finding a problem with it?

Cheers,
Don
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