From 4720bb4a5c0459489f6db99e4f4ba5eee84d5404 Mon Sep 17 00:00:00 2001
From: Jonathan Peyton <jonathan.l.peyton@intel.com>
Date: Fri, 1 Jul 2016 17:37:49 +0000
Subject: [PATCH] Improve performance of #pragma omp single
EPCC Performance of single is considerably worse than plain barrier.
Adding a read-only check to the code before the atomic compare-and-store
helps considerably.
Patch by Terry Wilmarth.
Differential Revision: http://reviews.llvm.org/D21893
git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@274369 91177308-0d34-0410-b5e6-96231b3b80d8
---
runtime/src/kmp_runtime.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/runtime/src/kmp_runtime.c b/runtime/src/kmp_runtime.c
index 55d080b..71c80c3 100644
--- a/runtime/src/kmp_runtime.c
+++ b/runtime/src/kmp_runtime.c
@@ -777,8 +777,10 @@ __kmp_enter_single( int gtid, ident_t *id_ref, int push_ws )
single block
*/
/* TODO: Should this be acquire or release? */
- status = KMP_COMPARE_AND_STORE_ACQ32(&team->t.t_construct, old_this,
- th->th.th_local.this_construct);
+ if (team->t.t_construct == old_this) {
+ status = KMP_COMPARE_AND_STORE_ACQ32(&team->t.t_construct, old_this,
+ th->th.th_local.this_construct);
+ }
#if USE_ITT_BUILD
if ( __itt_metadata_add_ptr && __kmp_forkjoin_frames_mode == 3 && KMP_MASTER_GTID(gtid) &&
#if OMP_40_ENABLED
--
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