[PATCH v6 4/4] powerpc: atomic: Implement acquire/release/relaxed variants for cmpxchg
Boqun Feng
boqun.feng at gmail.com
Wed Dec 16 01:24:17 AEDT 2015
Implement cmpxchg{,64}_relaxed and atomic{,64}_cmpxchg_relaxed, based on
which _release variants can be built.
To avoid superfluous barriers in _acquire variants, we implement these
operations with assembly code rather use __atomic_op_acquire() to build
them automatically.
For the same reason, we keep the assembly implementation of fully
ordered cmpxchg operations.
However, we don't do the similar for _release, because that will require
putting barriers in the middle of ll/sc loops, which is probably a bad
idea.
Note cmpxchg{,64}_relaxed and atomic{,64}_cmpxchg_relaxed are not
compiler barriers.
Signed-off-by: Boqun Feng <boqun.feng at gmail.com>
---
arch/powerpc/include/asm/atomic.h | 10 +++
arch/powerpc/include/asm/cmpxchg.h | 149 ++++++++++++++++++++++++++++++++++++-
2 files changed, 158 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/atomic.h b/arch/powerpc/include/asm/atomic.h
index 409d3cf..fb8ce7e 100644
--- a/arch/powerpc/include/asm/atomic.h
+++ b/arch/powerpc/include/asm/atomic.h
@@ -176,6 +176,11 @@ static __inline__ int atomic_dec_return_relaxed(atomic_t *v)
#define atomic_dec_return_relaxed atomic_dec_return_relaxed
#define atomic_cmpxchg(v, o, n) (cmpxchg(&((v)->counter), (o), (n)))
+#define atomic_cmpxchg_relaxed(v, o, n) \
+ cmpxchg_relaxed(&((v)->counter), (o), (n))
+#define atomic_cmpxchg_acquire(v, o, n) \
+ cmpxchg_acquire(&((v)->counter), (o), (n))
+
#define atomic_xchg(v, new) (xchg(&((v)->counter), new))
#define atomic_xchg_relaxed(v, new) xchg_relaxed(&((v)->counter), (new))
@@ -444,6 +449,11 @@ static __inline__ long atomic64_dec_if_positive(atomic64_t *v)
}
#define atomic64_cmpxchg(v, o, n) (cmpxchg(&((v)->counter), (o), (n)))
+#define atomic64_cmpxchg_relaxed(v, o, n) \
+ cmpxchg_relaxed(&((v)->counter), (o), (n))
+#define atomic64_cmpxchg_acquire(v, o, n) \
+ cmpxchg_acquire(&((v)->counter), (o), (n))
+
#define atomic64_xchg(v, new) (xchg(&((v)->counter), new))
#define atomic64_xchg_relaxed(v, new) xchg_relaxed(&((v)->counter), (new))
diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
index 17c7e14..cae4fa8 100644
--- a/arch/powerpc/include/asm/cmpxchg.h
+++ b/arch/powerpc/include/asm/cmpxchg.h
@@ -181,6 +181,56 @@ __cmpxchg_u32_local(volatile unsigned int *p, unsigned long old,
return prev;
}
+static __always_inline unsigned long
+__cmpxchg_u32_relaxed(u32 *p, unsigned long old, unsigned long new)
+{
+ unsigned long prev;
+
+ __asm__ __volatile__ (
+"1: lwarx %0,0,%2 # __cmpxchg_u32_relaxed\n"
+" cmpw 0,%0,%3\n"
+" bne- 2f\n"
+ PPC405_ERR77(0, %2)
+" stwcx. %4,0,%2\n"
+" bne- 1b\n"
+"2:"
+ : "=&r" (prev), "+m" (*p)
+ : "r" (p), "r" (old), "r" (new)
+ : "cc");
+
+ return prev;
+}
+
+/*
+ * cmpxchg family don't have order guarantee if cmp part fails, therefore we
+ * can avoid superfluous barriers if we use assembly code to implement
+ * cmpxchg() and cmpxchg_acquire(), however we don't do the similar for
+ * cmpxchg_release() because that will result in putting a barrier in the
+ * middle of a ll/sc loop, which is probably a bad idea. For example, this
+ * might cause the conditional store more likely to fail.
+ */
+static __always_inline unsigned long
+__cmpxchg_u32_acquire(u32 *p, unsigned long old, unsigned long new)
+{
+ unsigned long prev;
+
+ __asm__ __volatile__ (
+"1: lwarx %0,0,%2 # __cmpxchg_u32_acquire\n"
+" cmpw 0,%0,%3\n"
+" bne- 2f\n"
+ PPC405_ERR77(0, %2)
+" stwcx. %4,0,%2\n"
+" bne- 1b\n"
+ PPC_ACQUIRE_BARRIER
+ "\n"
+"2:"
+ : "=&r" (prev), "+m" (*p)
+ : "r" (p), "r" (old), "r" (new)
+ : "cc", "memory");
+
+ return prev;
+}
+
#ifdef CONFIG_PPC64
static __always_inline unsigned long
__cmpxchg_u64(volatile unsigned long *p, unsigned long old, unsigned long new)
@@ -224,6 +274,46 @@ __cmpxchg_u64_local(volatile unsigned long *p, unsigned long old,
return prev;
}
+
+static __always_inline unsigned long
+__cmpxchg_u64_relaxed(u64 *p, unsigned long old, unsigned long new)
+{
+ unsigned long prev;
+
+ __asm__ __volatile__ (
+"1: ldarx %0,0,%2 # __cmpxchg_u64_relaxed\n"
+" cmpd 0,%0,%3\n"
+" bne- 2f\n"
+" stdcx. %4,0,%2\n"
+" bne- 1b\n"
+"2:"
+ : "=&r" (prev), "+m" (*p)
+ : "r" (p), "r" (old), "r" (new)
+ : "cc");
+
+ return prev;
+}
+
+static __always_inline unsigned long
+__cmpxchg_u64_acquire(u64 *p, unsigned long old, unsigned long new)
+{
+ unsigned long prev;
+
+ __asm__ __volatile__ (
+"1: ldarx %0,0,%2 # __cmpxchg_u64_acquire\n"
+" cmpd 0,%0,%3\n"
+" bne- 2f\n"
+" stdcx. %4,0,%2\n"
+" bne- 1b\n"
+ PPC_ACQUIRE_BARRIER
+ "\n"
+"2:"
+ : "=&r" (prev), "+m" (*p)
+ : "r" (p), "r" (old), "r" (new)
+ : "cc", "memory");
+
+ return prev;
+}
#endif
/* This function doesn't exist, so you'll get a linker error
@@ -262,6 +352,37 @@ __cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new,
return old;
}
+static __always_inline unsigned long
+__cmpxchg_relaxed(void *ptr, unsigned long old, unsigned long new,
+ unsigned int size)
+{
+ switch (size) {
+ case 4:
+ return __cmpxchg_u32_relaxed(ptr, old, new);
+#ifdef CONFIG_PPC64
+ case 8:
+ return __cmpxchg_u64_relaxed(ptr, old, new);
+#endif
+ }
+ __cmpxchg_called_with_bad_pointer();
+ return old;
+}
+
+static __always_inline unsigned long
+__cmpxchg_acquire(void *ptr, unsigned long old, unsigned long new,
+ unsigned int size)
+{
+ switch (size) {
+ case 4:
+ return __cmpxchg_u32_acquire(ptr, old, new);
+#ifdef CONFIG_PPC64
+ case 8:
+ return __cmpxchg_u64_acquire(ptr, old, new);
+#endif
+ }
+ __cmpxchg_called_with_bad_pointer();
+ return old;
+}
#define cmpxchg(ptr, o, n) \
({ \
__typeof__(*(ptr)) _o_ = (o); \
@@ -279,6 +400,23 @@ __cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new,
(unsigned long)_n_, sizeof(*(ptr))); \
})
+#define cmpxchg_relaxed(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) _o_ = (o); \
+ __typeof__(*(ptr)) _n_ = (n); \
+ (__typeof__(*(ptr))) __cmpxchg_relaxed((ptr), \
+ (unsigned long)_o_, (unsigned long)_n_, \
+ sizeof(*(ptr))); \
+})
+
+#define cmpxchg_acquire(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) _o_ = (o); \
+ __typeof__(*(ptr)) _n_ = (n); \
+ (__typeof__(*(ptr))) __cmpxchg_acquire((ptr), \
+ (unsigned long)_o_, (unsigned long)_n_, \
+ sizeof(*(ptr))); \
+})
#ifdef CONFIG_PPC64
#define cmpxchg64(ptr, o, n) \
({ \
@@ -290,7 +428,16 @@ __cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new,
BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
cmpxchg_local((ptr), (o), (n)); \
})
-#define cmpxchg64_relaxed cmpxchg64_local
+#define cmpxchg64_relaxed(ptr, o, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ cmpxchg_relaxed((ptr), (o), (n)); \
+})
+#define cmpxchg64_acquire(ptr, o, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ cmpxchg_acquire((ptr), (o), (n)); \
+})
#else
#include <asm-generic/cmpxchg-local.h>
#define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
--
2.6.4
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