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Subject: Re: [RFC][PATCH 1/4] perf: core, add group scheduling
 transactional APIs
From: Lin Ming <ming.m.lin@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, "eranian@gmail.com" <eranian@gmail.com>,
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       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
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       lkml <linux-kernel@vger.kernel.org>
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Date: Thu, 22 Apr 2010 17:19:02 +0800
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On Thu, 2010-04-22 at 16:24 +0800, Peter Zijlstra wrote:
> On Thu, 2010-04-22 at 15:51 +0800, Lin Ming wrote:
> > +       if (pmu->commit_txn) {
> > +               ret = pmu->commit_txn(pmu);
> > +               if (!ret) {
> > +                       if (pmu->stop_txn)
> > +                               pmu->stop_txn(pmu);
> > +
> > +                       return 0;
> > +               }
> > +       } 
> 
> I think we can mandate that if one of the _txn methods is available,
> they all are, it would be weird otherwise.
> 

How about below?

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index ffd2360..72ea25c 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -635,12 +635,16 @@ group_sched_in(struct perf_event *group_event,
 {
 	struct perf_event *event, *partial_group = NULL;
 	const struct pmu *pmu = group_event->pmu;
+	bool txn = false;
 	int ret;
 
 	if (group_event->state == PERF_EVENT_STATE_OFF)
 		return 0;
 
 	if (pmu->start_txn)
+		txn = true;
+
+	if (txn)
 		pmu->start_txn(pmu);
 
 	if (event_sched_in(group_event, cpuctx, ctx))
@@ -656,18 +660,17 @@ group_sched_in(struct perf_event *group_event,
 		}
 	}
 
-	if (pmu->commit_txn) {
+	if (txn) {
 		ret = pmu->commit_txn(pmu);
 		if (!ret) {
-			if (pmu->stop_txn)
-				pmu->stop_txn(pmu);
+			pmu->stop_txn(pmu);
 
 			return 0;
 		}
 	}
 
 group_error:
-	if (pmu->stop_txn)
+	if (txn)
 		pmu->stop_txn(pmu);
 
 	/*