2015-04-09 16:48:45

by David Ahern

Subject: [PATCH] perf tools: Fix 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 <[email protected]>
Signed-off-by: David Ahern <[email protected]>
Cc: Don Zickus <[email protected]>
---
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

2015-04-09 17:05:34

by Don Zickus

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 <[email protected]>

>
> Reported-by: Arnaldo Carvalho de Melo <[email protected]>
> Signed-off-by: David Ahern <[email protected]>
> Cc: Don Zickus <[email protected]>
> ---
> 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
>

2015-04-09 17:08:19

by David Ahern

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

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<[email protected]>
>

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

2015-04-11 06:37:19

by tip-bot for Vasyl Gomonovych

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

Commit-ID: 7764a385f60bd200304a33124bdb4e684caeabdf
Gitweb: http://git.kernel.org/tip/7764a385f60bd200304a33124bdb4e684caeabdf
Author: David Ahern <[email protected]>
AuthorDate: Thu, 9 Apr 2015 12:48:27 -0400
Committer: Arnaldo Carvalho de Melo <[email protected]>
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 <[email protected]>
Signed-off-by: David Ahern <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Acked-by: Don Zickus <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
---
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;