[PATCH 15/34] asm-generic: add __smp_xxx wrappers

Michael S. Tsirkin
2015-12-30T19:34:51Z

On !SMP, most architectures define their
barriers as compiler barriers.
On SMP, most need an actual barrier.

Make it possible to remove the code duplication for
!SMP by defining a low-level __smp_XXX barriers
which do not depend on the value of SMP, then
use them from asm-generic conditionally.

Besides reducing code duplication, these low level APIs will also be
useful for virtualization, where a barrier is sometimes needed even if
!SMP since we might be talking to another kernel on the same SMP system.

Both virtio and Xen drivers will benefit.

The smp_XXX variants should use __smp_XXX ones or barrier() depending on
SMP, identically for all architectures.

We keep ifndef guards around them for now - once all
architectures have been converted to use the generic
code, we'll be able to remove these.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
include/asm-generic/barrier.h | 91 ++++++++++++++++++++++++++++++++++++++-----
1 file changed, 82 insertions(+), 9 deletions(-)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 987b2e0..8752964 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -54,22 +54,38 @@
#define read_barrier_depends() do { } while (0)
#endif

+#ifndef __smp_mb
+#define __smp_mb() mb()
+#endif
+
+#ifndef __smp_rmb
+#define __smp_rmb() rmb()
+#endif
+
+#ifndef __smp_wmb
+#define __smp_wmb() wmb()
+#endif
+
+#ifndef __smp_read_barrier_depends
+#define __smp_read_barrier_depends() read_barrier_depends()
+#endif
+
#ifdef CONFIG_SMP

#ifndef smp_mb
-#define smp_mb() mb()
+#define smp_mb() __smp_mb()
#endif

#ifndef smp_rmb
-#define smp_rmb() rmb()
+#define smp_rmb() __smp_rmb()
#endif

#ifndef smp_wmb
-#define smp_wmb() wmb()
+#define smp_wmb() __smp_wmb()
#endif

#ifndef smp_read_barrier_depends
-#define smp_read_barrier_depends() read_barrier_depends()
+#define smp_read_barrier_depends() __smp_read_barrier_depends()
#endif

#else /* !CONFIG_SMP */
@@ -92,23 +108,78 @@

#endif /* CONFIG_SMP */

+#ifndef __smp_store_mb
+#define __smp_store_mb(var, value) do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
+#endif
+
+#ifndef __smp_mb__before_atomic
+#define __smp_mb__before_atomic() __smp_mb()
+#endif
+
+#ifndef __smp_mb__after_atomic
+#define __smp_mb__after_atomic() __smp_mb()
+#endif
+
+#ifndef __smp_store_release
+#define __smp_store_release(p, v) \
+do { \
+ compiletime_assert_atomic_type(*p); \
+ __smp_mb(); \
+ WRITE_ONCE(*p, v); \
+} while (0)
+#endif
+
+#ifndef __smp_load_acquire
+#define __smp_load_acquire(p) \
+({ \
+ typeof(*p) ___p1 = READ_ONCE(*p); \
+ compiletime_assert_atomic_type(*p); \
+ __smp_mb(); \
+ ___p1; \
+})
+#endif
+
+#ifdef CONFIG_SMP
+
+#ifndef smp_store_mb
+#define smp_store_mb(var, value) __smp_store_mb(var, value)
+#endif
+
+#ifndef smp_mb__before_atomic
+#define smp_mb__before_atomic() __smp_mb__before_atomic()
+#endif
+
+#ifndef smp_mb__after_atomic
+#define smp_mb__after_atomic() __smp_mb__after_atomic()
+#endif
+
+#ifndef smp_store_release
+#define smp_store_release(p, v) __smp_store_release(p, v)
+#endif
+
+#ifndef smp_load_acquire
+#define smp_load_acquire(p) __smp_load_acquire(p)
+#endif
+
+#else /* !CONFIG_SMP */
+
#ifndef smp_store_mb
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
#endif

#ifndef smp_mb__before_atomic
-#define smp_mb__before_atomic() smp_mb()
+#define smp_mb__before_atomic() barrier()
#endif

#ifndef smp_mb__after_atomic
-#define smp_mb__after_atomic() smp_mb()
+#define smp_mb__after_atomic() barrier()
#endif

#ifndef smp_store_release
#define smp_store_release(p, v) \
do { \
compiletime_assert_atomic_type(*p); \
- smp_mb(); \
+ barrier(); \
WRITE_ONCE(*p, v); \
} while (0)
#endif
@@ -118,10 +189,12 @@ do { \
({ \
typeof(*p) ___p1 = READ_ONCE(*p); \
compiletime_assert_atomic_type(*p); \
- smp_mb(); \
+ barrier(); \
___p1; \
})
#endif

+#endif
+
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_GENERIC_BARRIER_H */
--
MST