Satyam Sharma wrote:
From: Satyam Sharma <[email protected]>
[8/8] i386: bitops: smp_mb__{before, after}_clear_bit() definitions
From Documentation/atomic_ops.txt, those archs that require explicit
memory barriers around clear_bit() must also implement these two interfaces.
However, for i386, clear_bit() is a strict, locked, atomic and
un-reorderable operation and includes an implicit memory barrier already.
But these two functions have been wrongly defined as "barrier()" which is
a pointless _compiler optimization_ barrier, and only serves to make gcc
not do legitimate optimizations that it could have otherwise done.
So let's make these proper no-ops, because that's exactly what we require
these to be on the i386 platform.
No. clear_bit is not a compiler barrier on i386, thus smp_mb__before/after
must be.
Signed-off-by: Satyam Sharma <[email protected]>
Cc: David Howells <[email protected]>
Cc: Nick Piggin <[email protected]>
---
[ A similar optimization needs to be done in the atomic.h also.
Will submit that patch shortly. ]
include/asm-i386/bitops.h | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/asm-i386/bitops.h b/include/asm-i386/bitops.h
index 4f1fda5..42999eb 100644
--- a/include/asm-i386/bitops.h
+++ b/include/asm-i386/bitops.h
@@ -106,8 +106,8 @@ static inline void __clear_bit(int nr, unsigned long *addr)
* Bit operations are already serializing on x86.
* These must still be defined here for API completeness.
*/
-#define smp_mb__before_clear_bit() barrier()
-#define smp_mb__after_clear_bit() barrier()
+#define smp_mb__before_clear_bit() do {} while (0)
+#define smp_mb__after_clear_bit() do {} while (0)
/**
* __change_bit - Toggle a bit in memory
--
SUSE Labs, Novell Inc.
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