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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
Date: Mon, 28 Sep 2020 14:03:30 -0500
Message-Id: <20200928190334.40624-4-honnappa.nagarahalli@arm.com>
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<20200928190334.40624-1-honnappa.nagarahalli@arm.com>
Subject: [dpdk-dev] [PATCH v2 4/8] net/memif: relax the load of ring head
pointer for S2M ring
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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