[v2,2/8] net/memif: relax the load of ring tail pointer for M2S ring

Message ID 20200928190334.40624-2-honnappa.nagarahalli@arm.com
State New
Headers show
Series
  • [v2,1/8] net/memif: do not update local copy of tail in tx function
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Commit Message

Honnappa Nagarahalli Sept. 28, 2020, 7:03 p.m.
For M2S rings, ring->tail 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(-)

-- 
2.17.1

Patch

diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
index 130099f2e..8bacacaa8 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)
 		n_free = ring_size - slot +
 				__atomic_load_n(&ring->tail, __ATOMIC_ACQUIRE);
 	} else {
-		slot = __atomic_load_n(&ring->tail, __ATOMIC_ACQUIRE);
+		/* For M2S queues ring->tail 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->tail, __ATOMIC_RELAXED);
 		n_free = __atomic_load_n(&ring->head, __ATOMIC_ACQUIRE) - slot;
 	}