[PATCH] net/iavf: replace SMP barrier with thread fence

[Kathleen Capella]

Replace the SMP barrier with atomic thread fence for iavf hw ring scan
in the bulk Rx path.

This patch introduces a change to the iavf driver that was already added
to the i40e driver [1] as part of the adoption of the use of compiler
atomics.

[1] https://patches.dpdk.org/project/dpdk/patch/20210706065404.25137-3-
joyce.kong at arm.com/

Signed-off-by: Kathleen Capella <kathleen.capella at arm.com>
Reviewed-by: Joyce Kong <joyce.kong at arm.com>
---
 drivers/net/iavf/iavf_rxtx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/iavf/iavf_rxtx.c b/drivers/net/iavf/iavf_rxtx.c
index cb779879cb..47f12a9b28 100644
--- a/drivers/net/iavf/iavf_rxtx.c
+++ b/drivers/net/iavf/iavf_rxtx.c
@@ -1843,7 +1843,8 @@ iavf_rx_scan_hw_ring_flex_rxd(struct iavf_rx_queue *rxq)
 		for (j = IAVF_LOOK_AHEAD - 1; j >= 0; j--)
 			s[j] = rte_le_to_cpu_16(rxdp[j].wb.status_error0);
 
-		rte_smp_rmb();
+		/* This barrier is to order loads of different words in the descriptor */
+		rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
 
 		/* Compute how many contiguous DD bits were set */
 		for (j = 0, nb_dd = 0; j < IAVF_LOOK_AHEAD; j++) {
@@ -1946,7 +1947,8 @@ iavf_rx_scan_hw_ring(struct iavf_rx_queue *rxq)
 			       IAVF_RXD_QW1_STATUS_SHIFT;
 		}
 
-		rte_smp_rmb();
+		/* This barrier is to order loads of different words in the descriptor */
+		rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
 
 		/* Compute how many contiguous DD bits were set */
 		for (j = 0, nb_dd = 0; j < IAVF_LOOK_AHEAD; j++) {
-- 
2.17.1