Re: [PATCH] eal: add notes to SMP memory barrier APIs

[Mattias Rönnblom]

On 2023-06-21 08:44, Ruifeng Wang wrote:
The rte_smp_xx() APIs are deprecated. But it is not mentioned
in the function header.
Added notes in function header for clarification.
Signed-off-by: Ruifeng Wang <ruifeng.w...@arm.com>
---
  lib/eal/include/generic/rte_atomic.h | 15 +++++++++++++++
  1 file changed, 15 insertions(+)

diff --git a/lib/eal/include/generic/rte_atomic.h 
b/lib/eal/include/generic/rte_atomic.h
index 58df843c54..542a2c16ff 100644
--- a/lib/eal/include/generic/rte_atomic.h
+++ b/lib/eal/include/generic/rte_atomic.h
@@ -55,6 +55,11 @@ static inline void rte_rmb(void);
   * Guarantees that the LOAD and STORE operations that precede the
   * rte_smp_mb() call are globally visible across the lcores
   * before the LOAD and STORE operations that follows it.
+ *
+ * @note
+ *  This function is deprecated. It adds complexity to the memory model
+ *  used by this project. C11 memory model should always be used.
+ *  rte_atomic_thread_fence() should be used instead.

It's somewhat confusing to learn I should use the C11 memory model, and 
then in the next sentence that I should call a function which is not in C11.

I think it would be helpful to say which memory_model parameters should 
be used to replace the rte_smp_*mb() calls, and if there are any 
difference in semantics between the Linux kernel-style barriers and 
their C11 (near-)equivalents.

Is there some particular reason these functions aren't marked 
__rte_deprecated? Too many warnings?

   */
  static inline void rte_smp_mb(void);
  
@@ -64,6 +69,11 @@ static inline void rte_smp_mb(void);
   * Guarantees that the STORE operations that precede the
   * rte_smp_wmb() call are globally visible across the lcores
   * before the STORE operations that follows it.
+ *
+ * @note
+ *  This function is deprecated. It adds complexity to the memory model
+ *  used by this project. C11 memory model should always be used.
+ *  rte_atomic_thread_fence() should be used instead.
   */
  static inline void rte_smp_wmb(void);
  
@@ -73,6 +83,11 @@ static inline void rte_smp_wmb(void);
   * Guarantees that the LOAD operations that precede the
   * rte_smp_rmb() call are globally visible across the lcores
   * before the LOAD operations that follows it.
+ *
+ * @note
+ *  This function is deprecated. It adds complexity to the memory model
+ *  used by this project. C11 memory model should always be used.
+ *  rte_atomic_thread_fence() should be used instead.
   */
  static inline void rte_smp_rmb(void);
  ///@}