[Openmp-commits] [openmp] 454d449 - [OpenMP] Use a memory fence before incrementing the dispatch buffer index (#87995)

[via Openmp-commits]

Author: Xing Xue
Date: 2024-04-16T13:13:49-04:00
New Revision: 454d4496970f665200b5b300578894d78405b6ca

URL: https://github.com/llvm/llvm-project/commit/454d4496970f665200b5b300578894d78405b6ca
DIFF: https://github.com/llvm/llvm-project/commit/454d4496970f665200b5b300578894d78405b6ca.diff

LOG: [OpenMP] Use a memory fence before incrementing the dispatch buffer index (#87995)

This patch uses a memory fence in function `__kmp_dispatch_next()` to
flush pending memory write invalidates before incrementing the
`volatile` variable `buffer_index` to fix intermittent time-outs of
OpenMP runtime LIT test cases `env/kmp_set_dispatch_buf.c` and
`worksharing/for/kmp_set_dispatch_buf.c`, noting that the same is needed
for incrementing `buffer_index` in function `__kmpc_next_section()`
(line 2600 of `kmp_dispatch.cpp`).

Added: 
    

Modified: 
    openmp/runtime/src/kmp_dispatch.cpp

Removed: 
    


################################################################################
diff  --git a/openmp/runtime/src/kmp_dispatch.cpp b/openmp/runtime/src/kmp_dispatch.cpp
index ac85b2b3f2fcd4..fc333765118179 100644
--- a/openmp/runtime/src/kmp_dispatch.cpp
+++ b/openmp/runtime/src/kmp_dispatch.cpp
@@ -2397,6 +2397,8 @@ static int __kmp_dispatch_next(ident_t *loc, int gtid, kmp_int32 *p_last,
           sh->u.s.ordered_iteration = 0;
         }
 
+        KMP_MB(); /* Flush all pending memory write invalidates.  */
+
         sh->buffer_index += __kmp_dispatch_num_buffers;
         KD_TRACE(100, ("__kmp_dispatch_next: T#%d change buffer_index:%d\n",
                        gtid, sh->buffer_index));