net/memif: relax load of ring head for M2S ring

For M2S rings, ring->head is updated by the receiver and eth_memif_rx
function is called in the context of receiving thread. The loads in
the receiver do not need to synchronize with its own stores.

Fixes: a2aafb9aa651 ("net/memif: optimize with one-way barrier")
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>
Reviewed-by: Jakub Grajciar <jgrajcia@cisco.com>

diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
index b72e249..6deab09 100644 (file)
--- a/drivers/net/memif/rte_eth_memif.c
+++ b/drivers/net/memif/rte_eth_memif.c
@@ -410,7 +410,11 @@ no_free_bufs:
 
 refill:
        if (type == MEMIF_RING_M2S) {
-               head = __atomic_load_n(&ring->head, __ATOMIC_ACQUIRE);
+               /* ring->head is updated by the receiver and this function
+                * is called in the context of receiver thread. The loads in
+                * the receiver do not need to synchronize with its own stores.
+                */
+               head = __atomic_load_n(&ring->head, __ATOMIC_RELAXED);
                n_slots = ring_size - head + mq->last_tail;
 
                while (n_slots--) {