[PATCH v2 7/7] ARM: atomics: define our SMP atomics in terms of _relaxed operations

Will Deacon
2015-07-16T15:32:38Z

By defining our SMP atomics in terms of relaxed operations, we gain
a small reduction in code size and have acquire/release/fence variants
generated automatically by the core code.

Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm/include/asm/atomic.h | 37 ++++++++++++++-------------------
arch/arm/include/asm/cmpxchg.h | 47 +++++++-----------------------------------
2 files changed, 24 insertions(+), 60 deletions(-)

diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
index e22c11970b7b..bc9da3a3ff5e 100644
--- a/arch/arm/include/asm/atomic.h
+++ b/arch/arm/include/asm/atomic.h
@@ -57,12 +57,11 @@ static inline void atomic_##op(int i, atomic_t *v) \
} \

#define ATOMIC_OP_RETURN(op, c_op, asm_op) \
-static inline int atomic_##op##_return(int i, atomic_t *v) \
+static inline int atomic_##op##_return_relaxed(int i, atomic_t *v) \
{ \
unsigned long tmp; \
int result; \
\
- smp_mb(); \
prefetchw(&v->counter); \
\
__asm__ __volatile__("@ atomic_" #op "_return\n" \
@@ -75,17 +74,17 @@ static inline int atomic_##op##_return(int i, atomic_t *v) \
: "r" (&v->counter), "Ir" (i) \
: "cc"); \
\
- smp_mb(); \
- \
return result; \
}

-static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
+#define atomic_add_return_relaxed atomic_add_return_relaxed
+#define atomic_sub_return_relaxed atomic_sub_return_relaxed
+
+static inline int atomic_cmpxchg_relaxed(atomic_t *ptr, int old, int new)
{
int oldval;
unsigned long res;

- smp_mb();
prefetchw(&ptr->counter);

do {
@@ -99,10 +98,9 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
: "cc");
} while (res);

- smp_mb();
-
return oldval;
}
+#define atomic_cmpxchg_relaxed atomic_cmpxchg_relaxed

static inline int __atomic_add_unless(atomic_t *v, int a, int u)
{
@@ -290,12 +288,12 @@ static inline void atomic64_##op(long long i, atomic64_t *v) \
} \

#define ATOMIC64_OP_RETURN(op, op1, op2) \
-static inline long long atomic64_##op##_return(long long i, atomic64_t *v) \
+static inline long long \
+atomic64_##op##_return_relaxed(long long i, atomic64_t *v) \
{ \
long long result; \
unsigned long tmp; \
\
- smp_mb(); \
prefetchw(&v->counter); \
\
__asm__ __volatile__("@ atomic64_" #op "_return\n" \
@@ -309,8 +307,6 @@ static inline long long atomic64_##op##_return(long long i, atomic64_t *v) \
: "r" (&v->counter), "r" (i) \
: "cc"); \
\
- smp_mb(); \
- \
return result; \
}

@@ -321,17 +317,19 @@ static inline long long atomic64_##op##_return(long long i, atomic64_t *v) \
ATOMIC64_OPS(add, adds, adc)
ATOMIC64_OPS(sub, subs, sbc)

+#define atomic64_add_return_relaxed atomic64_add_return_relaxed
+#define atomic64_sub_return_relaxed atomic64_sub_return_relaxed
+
#undef ATOMIC64_OPS
#undef ATOMIC64_OP_RETURN
#undef ATOMIC64_OP

-static inline long long atomic64_cmpxchg(atomic64_t *ptr, long long old,
- long long new)
+static inline long long
+atomic64_cmpxchg_relaxed(atomic64_t *ptr, long long old, long long new)
{
long long oldval;
unsigned long res;

- smp_mb();
prefetchw(&ptr->counter);

do {
@@ -346,17 +344,15 @@ static inline long long atomic64_cmpxchg(atomic64_t *ptr, long long old,
: "cc");
} while (res);

- smp_mb();
-
return oldval;
}
+#define atomic64_cmpxchg_relaxed atomic64_cmpxchg_relaxed

-static inline long long atomic64_xchg(atomic64_t *ptr, long long new)
+static inline long long atomic64_xchg_relaxed(atomic64_t *ptr, long long new)
{
long long result;
unsigned long tmp;

- smp_mb();
prefetchw(&ptr->counter);

__asm__ __volatile__("@ atomic64_xchg\n"
@@ -368,10 +364,9 @@ static inline long long atomic64_xchg(atomic64_t *ptr, long long new)
: "r" (&ptr->counter), "r" (new)
: "cc");

- smp_mb();
-
return result;
}
+#define atomic64_xchg_relaxed atomic64_xchg_relaxed

static inline long long atomic64_dec_if_positive(atomic64_t *v)
{
diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h
index 1692a05d3207..916a2744d5c6 100644
--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -35,7 +35,6 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
unsigned int tmp;
#endif

- smp_mb();
prefetchw((const void *)ptr);

switch (size) {
@@ -98,12 +97,11 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
__bad_xchg(ptr, size), ret = 0;
break;
}
- smp_mb();

return ret;
}

-#define xchg(ptr, x) ({ \
+#define xchg_relaxed(ptr, x) ({ \
(__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), \
sizeof(*(ptr))); \
})
@@ -117,6 +115,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
#error "SMP is not supported on this platform"
#endif

+#define xchg xchg_relaxed
+
/*
* cmpxchg_local and cmpxchg64_local are atomic wrt current CPU. Always make
* them available.
@@ -194,23 +194,11 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
return oldval;
}

-static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old,
- unsigned long new, int size)
-{
- unsigned long ret;
-
- smp_mb();
- ret = __cmpxchg(ptr, old, new, size);
- smp_mb();
-
- return ret;
-}
-
-#define cmpxchg(ptr,o,n) ({ \
- (__typeof__(*(ptr)))__cmpxchg_mb((ptr), \
- (unsigned long)(o), \
- (unsigned long)(n), \
- sizeof(*(ptr))); \
+#define cmpxchg_relaxed(ptr,o,n) ({ \
+ (__typeof__(*(ptr)))__cmpxchg((ptr), \
+ (unsigned long)(o), \
+ (unsigned long)(n), \
+ sizeof(*(ptr))); \
})

static inline unsigned long __cmpxchg_local(volatile void *ptr,
@@ -273,25 +261,6 @@ static inline unsigned long long __cmpxchg64(unsigned long long *ptr,

#define cmpxchg64_local(ptr, o, n) cmpxchg64_relaxed((ptr), (o), (n))

-static inline unsigned long long __cmpxchg64_mb(unsigned long long *ptr,
- unsigned long long old,
- unsigned long long new)
-{
- unsigned long long ret;
-
- smp_mb();
- ret = __cmpxchg64(ptr, old, new);
- smp_mb();
-
- return ret;
-}
-
-#define cmpxchg64(ptr, o, n) ({ \
- (__typeof__(*(ptr)))__cmpxchg64_mb((ptr), \
- (unsigned long long)(o), \
- (unsigned long long)(n)); \
-})
-
#endif /* __LINUX_ARM_ARCH__ >= 6 */

#endif /* __ASM_ARM_CMPXCHG_H */
--
2.1.4