[patch 6/9] mutex subsystem, switch ARM to use the xchg based implementation

[Ingo Molnar <mingo@elte.hu>]

as noted by Nicolas Pitre, atomic_[inc/dec]_call_if_[nonpositive/negative]()
atomic methods are slow on ARM, because they can only be implemented via
disabling interrupts. So tell the mutex code that we prefer atomic_xchg().

[ we still pull in asm-generic/atomic-call-if.h, so that they remain
  generally available primitives - even though unused on ARM at the
  moment. ]

Signed-off-by: Ingo Molnar <mingo@elte.hu>

----

 include/asm-arm/atomic.h |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

Index: linux/include/asm-arm/atomic.h
===================================================================
--- linux.orig/include/asm-arm/atomic.h
+++ linux/include/asm-arm/atomic.h
@@ -180,14 +180,16 @@ static inline void atomic_clear_mask(uns
 /*
  * Pull in the generic wrappers for atomic_dec_call_if_negative() and
  * atomic_inc_call_if_nonpositive().
- *
- * TODO: implement optimized primitives instead, or leave the generic
- * implementation in place, or use the __ARCH_WANT_XCHG_BASED_ATOMICS
- * mechanism to tell the generic mutex code to use the atomic_xchg()
- * based fastpath implementation.
  */
 #include <asm-generic/atomic-call-if.h>
 
+/*
+ * The atomic_[inc/dec]_call_if_[nonpositive/negative]() atomic methods
+ * are slow on ARM, because they can only be implemented via disabling
+ * interrupts. Tell the mutex code that we prefer atomic_xchg():
+ */
+#define __ARCH_WANT_XCHG_BASED_ATOMICS
+
 static inline int atomic_add_unless(atomic_t *v, int a, int u)
 {
 	int c, old;