linux-kernel - [PATCH] s390: more efficient smp barriers

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Date:	Sun, 10 Jan 2016 13:53:26 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-s390@...r.kernel.org
Subject: [PATCH] s390: more efficient smp barriers

As per: lkml.kernel.org/r/20150921112252.3c2937e1@...hwide
atomics imply a barrier on s390, so s390 should change
smp_mb__before_atomic and smp_mb__after_atomic to barrier() instead of
smp_mb() and hence should not use the generic versions.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Suggested-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---

This is on top of arch barrier cleanup patchset,
will be included in v3 of that patchset.

 arch/s390/include/asm/barrier.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index 4d26fa4..5c8db3c 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -45,6 +45,9 @@ do {									\
 	___p1;								\
 })
 
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
+
 #include <asm-generic/barrier.h>
 
 #endif /* __ASM_BARRIER_H */
-- 
MST