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

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

[David Ahern]

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).

Reported-by: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Signed-off-by: David Ahern <david.ahern@oracle.com>
Cc: Don Zickus <dzickus@redhat.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

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

[Don Zickus]

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@redhat.com>

> 
> Reported-by: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
> Signed-off-by: David Ahern <david.ahern@oracle.com>
> Cc: Don Zickus <dzickus@redhat.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
> 

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

[David Ahern]

On 4/9/15 11:05 AM, Don Zickus wrote:
> 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@redhat.com>
>

I believe this explains the performance delta you noticed with 
specjbb/jvm. Arnaldo is the one that figured out the performance hit is 
from cloning maps; from that analysis I realized what the goof was.

David

[tip:perf/core] perf tools: Fix synthesizing fork_event.ppid for non-main thread

[tip-bot for David Ahern]

Commit-ID:  7764a385f60bd200304a33124bdb4e684caeabdf
Gitweb:     http://git.kernel.org/tip/7764a385f60bd200304a33124bdb4e684caeabdf
Author:     David Ahern <david.ahern@oracle.com>
AuthorDate: Thu, 9 Apr 2015 12:48:27 -0400
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Fri, 10 Apr 2015 10:10:55 -0300

perf tools: Fix synthesizing fork_event.ppid for non-main thread

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).

Reported-by: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Signed-off-by: David Ahern <david.ahern@oracle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/r/1428598107-178999-1-git-send-email-david.ahern@oracle.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/event.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 5516236..9d09851 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;