linux-kernel - [PATCH 2/3] perf: clarify comment regarding event merging

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Message-Id: <1389311492-5059-3-git-send-email-cody@linux.vnet.ibm.com>
Date:	Thu,  9 Jan 2014 15:51:31 -0800
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: [PATCH 2/3] perf: clarify comment regarding event merging

There are actually 2 things about software events that allow us to
merge them: they never fail to schedule _and_ they have transaction
handlers we can (and do, when they are added to !sw groups) ignore. Note
both of these in the comment on adding sw events to !sw groups.

Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
---
 kernel/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f574401..e9f60d0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7065,7 +7065,8 @@ SYSCALL_DEFINE5(perf_event_open,
 			 *
 			 * Allow the addition of software events to !software
 			 * groups, this is safe because software events never
-			 * fail to schedule.
+			 * fail to schedule and have ignorable transaction
+			 * handlers ({start,cancel,commit}_txn).
 			 */
 			pmu = group_leader->pmu;
 		} else if (is_software_event(group_leader) &&
-- 
1.8.5.2

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