For zero-copy S2M rings, ring->head is updated by the sender and
eth_memif_tx_zc function is called in the context of sending thread.
The loads in the sender do not need to synchronize with its own stores.
Signed-off-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
Reviewed-by: Phil Yang <phil.y...@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
---
drivers/net/memif/rte_eth_memif.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/drivers/net/memif/rte_eth_memif.c
b/drivers/net/memif/rte_eth_memif.c
index 9babd073a..704350022 100644
--- a/drivers/net/memif/rte_eth_memif.c
+++ b/drivers/net/memif/rte_eth_memif.c
@@ -752,11 +752,13 @@ eth_memif_tx_zc(void *queue, struct rte_mbuf **bufs,
uint16_t nb_pkts)
memif_free_stored_mbufs(proc_private, mq);
/* ring type always MEMIF_RING_S2M */
- /* The ring->head acts as a guard variable between Tx and Rx
- * threads, so using load-acquire pairs with store-release
- * to synchronize it between threads.
+ /* 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_ACQUIRE);
+ slot = __atomic_load_n(&ring->head, __ATOMIC_RELAXED);
n_free = ring_size - slot + mq->last_tail;
int used_slots;
@@ -812,6 +814,10 @@ eth_memif_tx_zc(void *queue, struct rte_mbuf **bufs,
uint16_t nb_pkts)
no_free_slots:
/* ring type always MEMIF_RING_S2M */
+ /* The ring->head acts as a guard variable between Tx and Rx
+ * threads, so using store-release pairs with load-acquire
+ * in function eth_memif_rx for S2M rings.
+ */
__atomic_store_n(&ring->head, slot, __ATOMIC_RELEASE);
/* Send interrupt, if enabled. */
--
2.17.1
