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Subject: Re: [PATCH 2/4] perf_counter: optimize mmap/comm tracking
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>,
       Corey Ashford <cjashfor@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org
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	 <20090409085524.427173196@chello.nl>  <20090409091622.GA23636@elte.hu>
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Date: Thu, 09 Apr 2009 11:28:29 +0200
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On Thu, 2009-04-09 at 11:16 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> 
> > +static atomic_t nr_comm_tracking __read_mostly;
> 
> hm, nr_comm_tracking is not actually used by any fastpath - just 
> increased and then decreased.

Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -2018,7 +2018,12 @@ static void perf_counter_comm_event(stru
 
 void perf_counter_comm(struct task_struct *task)
 {
-	struct perf_comm_event comm_event = {
+	struct perf_comm_event comm_event;
+
+	if (!atomic_read(&nr_comm_tracking))
+		return;
+       
+	comm_event = (struct perf_comm_event){
 		.task	= task,
 		.event  = {
 			.header = { .type = PERF_EVENT_COMM, },