My program call rte_eth_dev_flow_ctrl_set after rte_eth_dev_start. I found that x710 dropped all packets(rx_dropped_packets in xstats).
I have used testpmd to confirm the problem:

diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
index da29858..eb11789 100755
--- a/app/test-pmd/testpmd.c
+++ b/app/test-pmd/testpmd.c
@@ -2928,6 +2928,16 @@ struct extmem_param {
 			continue;
 		}
 
+		{
+			struct rte_eth_fc_conf fc_conf = {
+				.autoneg = 0,
+				.mode = RTE_FC_NONE,
+			};
+
+			if (!rte_eth_dev_flow_ctrl_set(pi, &fc_conf))
+				printf("set port %d flow ctrl\n", pi);
+		}
+
 		if (port->port_status == RTE_PORT_HANDLING)
 			port->port_status = RTE_PORT_STARTED;
 		else

If I stop and start the port again, packet will be received as good.