From: Robert Richter Date: Wed, 29 Apr 2009 10:47:02 +0000 (+0200) Subject: perf_counter, x86: protect per-cpu variables with compile barriers only X-Git-Tag: firefly_0821_release~13973^2~350 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=527e26af3741a2168986d8b82653ffe173891324;p=firefly-linux-kernel-4.4.55.git 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 Cc: Paul Mackerras Acked-by: Peter Zijlstra LKML-Reference: <1241002046-8832-6-git-send-email-robert.richter@amd.com> Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c index 75a090394b6d..ad663d5ad2d9 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