linux-kernel - Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events

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Date:	Fri, 27 Mar 2015 14:10:54 -0600
From:	David Ahern <dsahern@...il.com>
To:	Don Zickus <dzickus@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	linux-kernel@...r.kernel.org, Joe Mario <jmario@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events

On 3/27/15 1:49 PM, Don Zickus wrote:
> diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> index 1c8fbc9..7ee3823 100644
> --- a/tools/perf/util/thread.c
> +++ b/tools/perf/util/thread.c
> @@ -187,6 +187,7 @@ static int thread__clone_map_groups(struct thread *thread,
>   	if (thread->pid_ == parent->pid_)
>   		return 0;

There's your answer ... the 2 lines above.

>
> +	printf("DON:\n");
>   	/* But this one is new process, copy maps. */
>   	for (i = 0; i < MAP__NR_TYPES; ++i)
>   		if (map_groups__clone(thread->mg, parent->mg, i) < 0)
>
> before David's patch, we do _not_ see any DON markers.  After David's patch
> we see a 1:1 match of DON markers to the number of threads currently running
> in the system.

Your "speed up" is based on the assumption that all synthesized threads 
are their own parent which is wrong. ie., ppid != tgid of the process.

Before ppid was getting initialized to -1. If you just make that change 
to revert to the -1:

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index d5efa5092ce6..ce4ca061c2e5 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -150,8 +150,8 @@ static int perf_event__synthesize_fork(struct 
perf_tool *tool,
  {
     memset(&event->fork, 0, sizeof(event->fork) + machine->id_hdr_size);

-   event->fork.ppid = tgid;
-   event->fork.ptid = tgid;
+   event->fork.ppid = -1;
+   event->fork.ptid = -1;
     event->fork.pid  = tgid;
     event->fork.tid  = pid;
     event->fork.header.type = PERF_RECORD_FORK;

You see the "DON" messages.

David
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