Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 527e26af authored by Robert Richter's avatar Robert Richter Committed by Ingo Molnar
Browse files

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: default avatarRobert Richter <robert.richter@amd.com>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1241002046-8832-6-git-send-email-robert.richter@amd.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 4295ee62

arch/x86/kernel/cpu/perf_counter.c

+2 −2
Original line number Diff line number Diff line
@@ -673,7 +673,7 @@ static int pmc_generic_enable(struct perf_counter *counter) 
	/*

	 * 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