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From: Steven Lariau <steven.lariau@arm.com>
To: Gage Eads <gage.eads@intel.com>,
Olivier Matz <olivier.matz@6wind.com>
Cc: dev@dpdk.org, nd@arm.com, dharmik.thakkar@arm.com,
Steven Lariau <steven.lariau@arm.com>
Date: Fri, 11 Sep 2020 16:29:36 +0100
Message-Id: <20200911152938.8019-4-steven.lariau@arm.com>
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References: <20200911152938.8019-1-steven.lariau@arm.com>
Subject: [dpdk-dev] [PATCH 3/5] lib/stack: remove redundant orderings for
list->len
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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@arm.com>
Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.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