From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by dpdk.org (Postfix) with ESMTP id 7DBFA4CE4; Mon, 17 Sep 2018 10:11:35 +0200 (CEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EDA8DED1; Mon, 17 Sep 2018 01:11:34 -0700 (PDT) Received: from net-arm-thunderx2.shanghai.arm.com (net-arm-thunderx2.shanghai.arm.com [10.169.40.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 89B773F5C0; Mon, 17 Sep 2018 01:11:33 -0700 (PDT) From: Gavin Hu To: dev@dpdk.org Cc: gavin.hu@arm.com, Honnappa.Nagarahalli@arm.com, steve.capper@arm.com, Ola.Liljedahl@arm.com, jerin.jacob@caviumnetworks.com, nd@arm.com, stable@dpdk.org Date: Mon, 17 Sep 2018 16:11:19 +0800 Message-Id: <1537171879-64390-4-git-send-email-gavin.hu@arm.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1537171879-64390-1-git-send-email-gavin.hu@arm.com> References: <20180917074735.28161-1-gavin.hu@arm.com> <1537171879-64390-1-git-send-email-gavin.hu@arm.com> Subject: [dpdk-stable] [PATCH v4 4/4] ring: move the atomic load of head above the loop X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 17 Sep 2018 08:11:35 -0000 In __rte_ring_move_prod_head, move the __atomic_load_n up and out of the do {} while loop as upon failure the old_head will be updated, another load is costly and not necessary. This helps a little on the latency,about 1~5%. Test result with the patch(two cores): SP/SC bulk enq/dequeue (size: 8): 5.64 MP/MC bulk enq/dequeue (size: 8): 9.58 SP/SC bulk enq/dequeue (size: 32): 1.98 MP/MC bulk enq/dequeue (size: 32): 2.30 Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option") Cc: stable@dpdk.org Signed-off-by: Gavin Hu Reviewed-by: Honnappa Nagarahalli Reviewed-by: Steve Capper Reviewed-by: Ola Liljedahl --- lib/librte_ring/rte_ring_c11_mem.h | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h index 0eae3b3..95cc508 100644 --- a/lib/librte_ring/rte_ring_c11_mem.h +++ b/lib/librte_ring/rte_ring_c11_mem.h @@ -61,13 +61,11 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp, unsigned int max = n; int success; + *old_head = __atomic_load_n(&r->prod.head, __ATOMIC_ACQUIRE); do { /* Reset n to the initial burst count */ n = max; - *old_head = __atomic_load_n(&r->prod.head, - __ATOMIC_ACQUIRE); - /* load-acquire synchronize with store-release of ht->tail * in update_tail. */ @@ -93,6 +91,7 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp, if (is_sp) r->prod.head = *new_head, success = 1; else + /* on failure, *old_head is updated */ success = __atomic_compare_exchange_n(&r->prod.head, old_head, *new_head, 0, __ATOMIC_ACQUIRE, @@ -134,13 +133,11 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc, int success; /* move cons.head atomically */ + *old_head = __atomic_load_n(&r->cons.head, __ATOMIC_ACQUIRE); do { /* Restore n as it may change every loop */ n = max; - *old_head = __atomic_load_n(&r->cons.head, - __ATOMIC_ACQUIRE); - /* this load-acquire synchronize with store-release of ht->tail * in update_tail. */ @@ -165,6 +162,7 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc, if (is_sc) r->cons.head = *new_head, success = 1; else + /* on failure, *old_head will be updated */ success = __atomic_compare_exchange_n(&r->cons.head, old_head, *new_head, 0, __ATOMIC_ACQUIRE, -- 2.7.4