[v2,5/8] net/memif: relax the load of ring head pointer for M2S zc ring
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Commit Message
For zero-copy M2S rings, ring->head is updated by the receiver
and eth_memif_rx_zc function is called in the context of
receiving thread. The loads in the receiver do not need to
synchronize with its own stores.
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 | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
@@ -514,11 +514,11 @@ eth_memif_rx_zc(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
/* Supply master with new buffers */
refill:
- /* 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.
+ /* 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_ACQUIRE);
+ head = __atomic_load_n(&ring->head, __ATOMIC_RELAXED);
n_slots = ring_size - head + mq->last_tail;
if (n_slots < 32)
@@ -543,6 +543,10 @@ eth_memif_rx_zc(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
(uint8_t *)proc_private->regions[d0->region]->addr;
}
no_free_mbufs:
+ /* 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_tx.
+ */
__atomic_store_n(&ring->head, head, __ATOMIC_RELEASE);
mq->n_pkts += n_rx_pkts;