On 2023-03-17 17:37, Ondřej Surý via lttng-dev wrote:
Instead of using CMM_ACCESS_ONCE() with memory barriers, use __atomic
builtins with relaxed memory ordering to implement CMM_LOAD_SHARED() and
CMM_STORE_SHARED().
Signed-off-by: Ondřej Surý <ond...@sury.org>
---
include/urcu/system.h | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/include/urcu/system.h b/include/urcu/system.h
index faae390..99e7443 100644
--- a/include/urcu/system.h
+++ b/include/urcu/system.h
@@ -26,7 +26,7 @@
* Identify a shared load. A cmm_smp_rmc() or cmm_smp_mc() should come
* before the load.
*/
-#define _CMM_LOAD_SHARED(p) CMM_ACCESS_ONCE(p)
+#define _CMM_LOAD_SHARED(p) __atomic_load_n(&(p), __ATOMIC_RELAXED)
/*
* Load a data from shared memory, doing a cache flush if required.
@@ -42,7 +42,7 @@
* Identify a shared store. A cmm_smp_wmc() or cmm_smp_mc() should
* follow the store.
*/
-#define _CMM_STORE_SHARED(x, v) __extension__ ({ CMM_ACCESS_ONCE(x) =
(v); })
+#define _CMM_STORE_SHARED(x, v) __atomic_store_n(&(x), (v),
__ATOMIC_RELAXED)
__atomic_store_n() is void. _CMM_STORE_SHARED() should evaluate to (v)
(unless we decide to change the semantic, which I would rather avoid).
Thanks,
Mathieu
/*
* Store v into x, where x is located in shared memory. Performs the
@@ -51,9 +51,8 @@
#define CMM_STORE_SHARED(x, v)
\
__extension__ \
({ \
- __typeof__(x) _v = _CMM_STORE_SHARED(x, v); \
+ _CMM_STORE_SHARED(x, v); \
cmm_smp_wmc(); \
- _v = _v; /* Work around clang "unused result" */ \
})
#endif /* _URCU_SYSTEM_H */
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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