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 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/if all architectures are converted to use the generic code, we'll be able to remove these. Suggested-by: Peter Zijlstra <pet...@infradead.org> Signed-off-by: Michael S. Tsirkin <m...@redhat.com> Acked-by: Arnd Bergmann <a...@arndb.de> --- 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 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev