From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753347AbZHMOPT (ORCPT ); Thu, 13 Aug 2009 10:15:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752316AbZHMOPS (ORCPT ); Thu, 13 Aug 2009 10:15:18 -0400 Received: from casper.infradead.org ([85.118.1.10]:53508 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751600AbZHMOPR (ORCPT ); Thu, 13 Aug 2009 10:15:17 -0400 Subject: [PATCH] perf_counter: Report the cloning task as parent on perf_counter_fork() From: Peter Zijlstra To: Pekka Enberg Cc: mingo@elte.hu, Arnaldo Carvalho de Melo , paulus@samba.org, linux-kernel@vger.kernel.org, Anton Blanchard , Arjan van de Ven In-Reply-To: <1250155708.6052.2.camel@penberg-laptop> References: <1250155708.6052.2.camel@penberg-laptop> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Thu, 13 Aug 2009 16:14:42 +0200 Message-Id: <1250172882.5241.62.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A bug in (9f498cc: perf_counter: Full task tracing) makes profiling multi-threaded apps it go belly up. [ output as: (PID:TID):(PPID:PTID) ] # ./perf report -D | grep FORK 0x4b0 [0x18]: PERF_EVENT_FORK: (3237:3237):(3236:3236) 0xa10 [0x18]: PERF_EVENT_FORK: (3237:3238):(3236:3236) 0xa70 [0x18]: PERF_EVENT_FORK: (3237:3239):(3236:3236) 0xad0 [0x18]: PERF_EVENT_FORK: (3237:3240):(3236:3236) 0xb18 [0x18]: PERF_EVENT_FORK: (3237:3241):(3236:3236) Shows us that the test (27d028d perf report: Update for the new FORK/EXIT events) in builtin-report.c: /* * A thread clone will have the same PID for both * parent and child. */ if (thread == parent) return 0; Will clearly fail. The problem is that perf_counter_fork() reports the actual parent, instead of the cloning thread. Fixing that (with the below patch), yields: # ./perf report -D | grep FORK 0x4c8 [0x18]: PERF_EVENT_FORK: (1590:1590):(1589:1589) 0xbd8 [0x18]: PERF_EVENT_FORK: (1590:1591):(1590:1590) 0xc80 [0x18]: PERF_EVENT_FORK: (1590:1592):(1590:1590) 0x3338 [0x18]: PERF_EVENT_FORK: (1590:1593):(1590:1590) 0x66b0 [0x18]: PERF_EVENT_FORK: (1590:1594):(1590:1590) Which both makes more sense and doesn't confuse perf report anymore. Reported-by: Pekka Enberg Signed-off-by: Peter Zijlstra --- perf_counter.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) Index: linux-2.6/kernel/perf_counter.c =================================================================== --- linux-2.6.orig/kernel/perf_counter.c +++ linux-2.6/kernel/perf_counter.c @@ -3024,10 +3024,10 @@ static void perf_counter_task_output(str return; task_event->event.pid = perf_counter_pid(counter, task); - task_event->event.ppid = perf_counter_pid(counter, task->real_parent); + task_event->event.ppid = perf_counter_pid(counter, current); task_event->event.tid = perf_counter_tid(counter, task); - task_event->event.ptid = perf_counter_tid(counter, task->real_parent); + task_event->event.ptid = perf_counter_tid(counter, current); perf_output_put(&handle, task_event->event); perf_output_end(&handle);