linux-kernel - [tip:perfcounters/core] perf_counter, x86: protect per-cpu variables with compile barriers only

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Date:	Wed, 29 Apr 2009 13:04:16 GMT
From:	tip-bot for Robert Richter <robert.richter@....com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, robert.richter@....com, a.p.zijlstra@...llo.nl,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:perfcounters/core] perf_counter, x86: protect per-cpu variables with compile barriers only

Commit-ID:  527e26af3741a2168986d8b82653ffe173891324
Gitweb:     http://git.kernel.org/tip/527e26af3741a2168986d8b82653ffe173891324
Author:     Robert Richter <robert.richter@....com>
AuthorDate: Wed, 29 Apr 2009 12:47:02 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 29 Apr 2009 14:51:02 +0200

perf_counter, x86: protect per-cpu variables with compile barriers only

Per-cpu variables needn't to be protected with cpu barriers
(smp_wmb()). Protection is only needed for preemption on the same cpu
(rescheduling or the nmi handler). This can be done using a compiler
barrier only.

[ Impact: micro-optimization ]

Signed-off-by: Robert Richter <robert.richter@....com>
Cc: Paul Mackerras <paulus@...ba.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1241002046-8832-6-git-send-email-robert.richter@....com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/kernel/cpu/perf_counter.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 75a0903..ad663d5 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -673,7 +673,7 @@ try_generic:
 	/*
 	 * Make it visible before enabling the hw:
 	 */
-	smp_wmb();
+	barrier();
 
 	__hw_perf_counter_set_period(counter, hwc, idx);
 	__pmc_generic_enable(counter, hwc, idx);
@@ -745,7 +745,7 @@ static void pmc_generic_disable(struct perf_counter *counter)
 	 * Make sure the cleared pointer becomes visible before we
 	 * (potentially) free the counter:
 	 */
-	smp_wmb();
+	barrier();
 
 	/*
 	 * Drain the remaining delta count out of a counter
--
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