linux-kernel - [patch 3/5] perf_counter: Log vfork as a fork event

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Message-Id: <20090716104817.589309391@samba.org>
Date:	Thu, 16 Jul 2009 20:42:50 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org,
	fweisbec@...il.com
Cc:	linux-kernel@...r.kernel.org
Subject: [patch 3/5] perf_counter: Log vfork as a fork event

Right now we don't output vfork events. Even though we should always see an
exec after a vfork, we may get perfcounter samples between the vfork and exec.
These samples can lead to some confusion when parsing perfcounter data.

To keep things consistent we should always log a fork event. It will result
in a little more log data, but is less confusing to trace parsing tools.

Signed-off-by: Anton Blanchard <anton@...ba.org>
---

It took me a while to realise this wasn't a bug in some trace parsing
code I wrote, or an issue with samples being dropped :)

Index: linux.trees.git/kernel/fork.c
===================================================================
--- linux.trees.git.orig/kernel/fork.c	2009-07-15 10:00:30.000000000 +1000
+++ linux.trees.git/kernel/fork.c	2009-07-15 10:01:28.000000000 +1000
@@ -1407,14 +1407,11 @@
 		if (clone_flags & CLONE_VFORK) {
 			p->vfork_done = &vfork;
 			init_completion(&vfork);
-		} else if (!(clone_flags & CLONE_VM)) {
-			/*
-			 * vfork will do an exec which will call
-			 * set_task_comm()
-			 */
-			perf_counter_fork(p);
 		}
 
+		if (!(clone_flags & CLONE_THREAD))
+			perf_counter_fork(p);
+
 		audit_finish_fork(p);
 		tracehook_report_clone(regs, clone_flags, nr, p);
 

-- 

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