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>
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 @@
/*
* 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 @@
* 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