From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id 3449DA04BB; Fri, 11 Sep 2020 17:31:58 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 1AD311C11D; Fri, 11 Sep 2020 17:31:37 +0200 (CEST) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by dpdk.org (Postfix) with ESMTP id 302771C11C for ; Fri, 11 Sep 2020 17:31:35 +0200 (CEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A5A131063; Fri, 11 Sep 2020 08:31:34 -0700 (PDT) Received: from localhost.localdomain (unknown [10.57.10.210]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2800F3F73C; Fri, 11 Sep 2020 08:31:32 -0700 (PDT) From: Steven Lariau To: Gage Eads , Olivier Matz Cc: dev@dpdk.org, nd@arm.com, dharmik.thakkar@arm.com, Steven Lariau Date: Fri, 11 Sep 2020 16:29:38 +0100 Message-Id: <20200911152938.8019-6-steven.lariau@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200911152938.8019-1-steven.lariau@arm.com> References: <20200911152938.8019-1-steven.lariau@arm.com> Subject: [dpdk-dev] [PATCH 5/5] lib/stack: remove pop cas release ordering X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Replace the store-release by relaxed for the CAS success at the end of pop. Release isn't needed, because there is not write to data that need to be synchronized. The only preceding write is when the length is decreased, but the length CAS loop already ensures the right synchronization. The situation to avoid is when a thread sees the old length but the new list, that doesn't have enough items for pop to success. But the CAS success on length before the pop loop ensures any core reads and updates the latest length, preventing this situation. The store-release is also used to make sure that the items are read before the head is updated, in order to prevent a core in pop to read an incorrect value because another core rewrites it with push. But this isn't needed, because items are read only when removed from the used list. Right after this, they are pushed to the free list, and the store-release in push makes sure the items are read before they are visible in the free list. Signed-off-by: Steven Lariau Reviewed-by: Dharmik Thakkar Reviewed-by: Ruifeng Wang --- lib/librte_stack/rte_stack_lf_c11.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/librte_stack/rte_stack_lf_c11.h b/lib/librte_stack/rte_stack_lf_c11.h index adb9f590d..8800db42e 100644 --- a/lib/librte_stack/rte_stack_lf_c11.h +++ b/lib/librte_stack/rte_stack_lf_c11.h @@ -145,7 +145,7 @@ __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list, (rte_int128_t *)&list->head, (rte_int128_t *)&old_head, (rte_int128_t *)&new_head, - 0, __ATOMIC_RELEASE, + 0, __ATOMIC_RELAXED, __ATOMIC_RELAXED); } while (success == 0); -- 2.17.1