patches for DPDK stable branches
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From: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
To: dev@dpdk.org, honnappa.nagarahalli@arm.com, phil.yang@arm.com,
	jgrajcia@cisco.com, ferruh.yigit@intel.com
Cc: nd@arm.com, stable@dpdk.org
Subject: [dpdk-stable] [PATCH v2 4/8] net/memif: relax the load of ring head pointer for S2M ring
Date: Mon, 28 Sep 2020 14:03:30 -0500
Message-ID: <20200928190334.40624-4-honnappa.nagarahalli@arm.com> (raw)
In-Reply-To: <20200928190334.40624-1-honnappa.nagarahalli@arm.com>

For S2M rings, ring->head is updated by the sender and eth_memif_tx
function is called in the context of sending thread. The loads in
the sender do not need to synchronize with its own stores.

Fixes: a2aafb9aa651 ("net/memif: optimize with one-way barrier")
Cc: phil.yang@arm.com
Cc: stable@dpdk.org

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
 drivers/net/memif/rte_eth_memif.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
index 159b45180..96db76121 100644
--- a/drivers/net/memif/rte_eth_memif.c
+++ b/drivers/net/memif/rte_eth_memif.c
@@ -585,7 +585,13 @@ eth_memif_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	mask = ring_size - 1;
 
 	if (type == MEMIF_RING_S2M) {
-		slot = __atomic_load_n(&ring->head, __ATOMIC_ACQUIRE);
+		/* For S2M queues ring->head is updated by the sender and
+		 * this function is called in the context of sending thread.
+		 * The loads in the sender do not need to synchronize with
+		 * its own stores. Hence, the following load can be a
+		 * relaxed load.
+		 */
+		slot = __atomic_load_n(&ring->head, __ATOMIC_RELAXED);
 		n_free = ring_size - slot +
 				__atomic_load_n(&ring->tail, __ATOMIC_ACQUIRE);
 	} else {
-- 
2.17.1


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21 19:22 [dpdk-stable] [PATCH 1/4] net/memif: do not update local copy of tail in tx function Honnappa Nagarahalli
2020-09-21 19:22 ` [dpdk-stable] [PATCH 2/4] net/memif: relax the load of ring tail pointer for M2S ring Honnappa Nagarahalli
2020-09-21 19:22 ` [dpdk-stable] [PATCH 3/4] net/memif: relax the load of ring head pointer for S2M ring Honnappa Nagarahalli
2020-09-21 19:22 ` [dpdk-stable] [PATCH 4/4] net/memif: relax the load of ring head pointer for M2S ring Honnappa Nagarahalli
2020-09-28 19:03 ` [dpdk-stable] [PATCH v2 1/8] net/memif: do not update local copy of tail in tx function Honnappa Nagarahalli
2020-09-28 19:03   ` [dpdk-stable] [PATCH v2 2/8] net/memif: relax the load of ring tail pointer for M2S ring Honnappa Nagarahalli
2020-09-28 19:03   ` [dpdk-stable] [PATCH v2 3/8] net/memif: relax the load of ring head " Honnappa Nagarahalli
2020-09-28 19:03   ` Honnappa Nagarahalli [this message]
2020-09-28 20:53   ` [dpdk-stable] [dpdk-dev] [PATCH v2 1/8] net/memif: do not update local copy of tail in tx function Stephen Hemminger
2020-09-29  5:24     ` Honnappa Nagarahalli
2020-10-07 17:08   ` [dpdk-stable] " Honnappa Nagarahalli
2020-10-09 11:23     ` Jakub Grajciar -X (jgrajcia - PANTHEON TECH SRO at Cisco)
2020-10-09 15:59       ` Ferruh Yigit

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