[dpdk-dev] [PATCH v2 3/5] lib/stack: remove redundant orderings for list->len

[Steven Lariau]

The load-acquire of list->len on pop function is redundant.
Only the CAS success needs to be load-acquire.
It synchronizes with the store release in push, to ensure that the
updated head is visible when the new length is visible.
Without this, one thread in pop could see the increased length but the
old list, which doesn't have enough items yet for pop to succeed.

Signed-off-by: Steven Lariau <steven.lariau at arm.com>
Reviewed-by: Dharmik Thakkar <dharmik.thakkar at arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
Acked-by: Gage Eads <gage.eads at intel.com>
---
 lib/librte_stack/rte_stack_lf_c11.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/librte_stack/rte_stack_lf_c11.h b/lib/librte_stack/rte_stack_lf_c11.h
index 82b7287f1..2bc639419 100644
--- a/lib/librte_stack/rte_stack_lf_c11.h
+++ b/lib/librte_stack/rte_stack_lf_c11.h
@@ -80,7 +80,7 @@ __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
 	int success;
 
 	/* Reserve num elements, if available */
-	len = __atomic_load_n(&list->len, __ATOMIC_ACQUIRE);
+	len = __atomic_load_n(&list->len, __ATOMIC_RELAXED);
 
 	while (1) {
 		/* Does the list contain enough elements? */
@@ -91,7 +91,7 @@ __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
 		if (__atomic_compare_exchange_n(&list->len,
 						&len, len - num,
 						1, __ATOMIC_ACQUIRE,
-						__ATOMIC_ACQUIRE))
+						__ATOMIC_RELAXED))
 			break;
 	}
 
-- 
2.17.1