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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>
Subject: [dpdk-dev] [PATCH 3/5] lib/stack: remove redundant orderings for list->len
Date: Fri, 11 Sep 2020 16:29:36 +0100
Message-ID: <20200911152938.8019-4-steven.lariau@arm.com> (raw)
In-Reply-To: <20200911152938.8019-1-steven.lariau@arm.com>

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


  parent reply	other threads:[~2020-09-11 15:31 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-11 15:29 [dpdk-dev] [PATCH 0/5] lib/stack: improve lockfree C11 implementation Steven Lariau
2020-09-11 15:29 ` [dpdk-dev] [PATCH 1/5] lib/stack: fix inconsistent weak / strong cas Steven Lariau
2020-09-21 17:16   ` Eads, Gage
2020-09-11 15:29 ` [dpdk-dev] [PATCH 2/5] lib/stack: remove push acquire fence Steven Lariau
2020-09-21 17:16   ` Eads, Gage
2020-09-11 15:29 ` Steven Lariau [this message]
2020-09-21 17:16   ` [dpdk-dev] [PATCH 3/5] lib/stack: remove redundant orderings for list->len Eads, Gage
2020-09-11 15:29 ` [dpdk-dev] [PATCH 4/5] lib/stack: reload head when pop fails Steven Lariau
2020-09-21 17:16   ` Eads, Gage
2020-09-11 15:29 ` [dpdk-dev] [PATCH 5/5] lib/stack: remove pop cas release ordering Steven Lariau
2020-09-21 17:17   ` Eads, Gage
2020-09-25 14:27     ` David Marchand
2020-09-25 17:43 ` [dpdk-dev] [PATCH v2 0/5] lib/stack: improve lockfree C11 implementation Steven Lariau
2020-09-25 17:43   ` [dpdk-dev] [PATCH v2 1/5] lib/stack: fix inconsistent weak / strong cas Steven Lariau
2020-09-28 10:22     ` David Marchand
2020-09-28 15:58       ` Eads, Gage
2020-09-25 17:43   ` [dpdk-dev] [PATCH v2 2/5] lib/stack: remove push acquire fence Steven Lariau
2020-09-25 17:43   ` [dpdk-dev] [PATCH v2 3/5] lib/stack: remove redundant orderings for list->len Steven Lariau
2020-09-25 17:43   ` [dpdk-dev] [PATCH v2 4/5] lib/stack: reload head when pop fails Steven Lariau
2020-09-25 17:43   ` [dpdk-dev] [PATCH v2 5/5] lib/stack: remove pop cas release ordering Steven Lariau
2020-09-25 17:57     ` Eads, Gage
2020-09-30 19:14   ` [dpdk-dev] [PATCH v2 0/5] lib/stack: improve lockfree C11 implementation David Marchand

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