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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@amd.com>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1241002046-8832-6-git-send-email-robert.richter@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Robert Richter 2009-04-29 12:47:02 +02:00 committed by Ingo Molnar
parent 4295ee6266
commit 527e26af37
1 changed files with 2 additions and 2 deletions
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4
arch/x86/kernel/cpu/perf_counter.c
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@ -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