[PATCH v1] app/testpmd: use Tx preparation in txonly engine

[Kaiwen Deng <kaiwenx.deng@intel.com>]

Txonly forwarding engine does not call the Tx preparation API
before transmitting packets. This may cause some problems.

TSO breaks when MSS spans more than 8 data fragments. Those
packets will be dropped by Tx preparation API, but it will cause
MDD event if txonly forwarding engine does not call the Tx preparation
API before transmitting packets.

We can reproduce this issue by these steps list blow on ICE and I40e.

./x86_64-native-linuxapp-gcc/app/dpdk-testpmd -c 0xf -n 4 -- -i
--tx-offloads=0x00008000

testpmd>set txpkts 64,128,256,512,64,128,256,512,512
testpmd>set burst 1
testpmd>start tx_first 1

This commit will use Tx preparation API in txonly forwarding engine.

Fixes: 655131ccf727 ("app/testpmd: factorize fwd engines Tx")
Cc: stable@dpdk.org

Signed-off-by: Kaiwen Deng <kaiwenx.deng@intel.com>
---
 app/test-pmd/txonly.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/app/test-pmd/txonly.c b/app/test-pmd/txonly.c
index c2b88764be..60d69be3f6 100644
--- a/app/test-pmd/txonly.c
+++ b/app/test-pmd/txonly.c
@@ -339,6 +339,7 @@ pkt_burst_transmit(struct fwd_stream *fs)
 	struct rte_ether_hdr eth_hdr;
 	uint16_t nb_tx;
 	uint16_t nb_pkt;
+	uint16_t nb_prep;
 	uint16_t vlan_tci, vlan_tci_outer;
 	uint64_t ol_flags = 0;
 	uint64_t tx_offloads;
@@ -396,7 +397,17 @@ pkt_burst_transmit(struct fwd_stream *fs)
 	if (nb_pkt == 0)
 		return false;
 
-	nb_tx = common_fwd_stream_transmit(fs, pkts_burst, nb_pkt);
+	nb_prep = rte_eth_tx_prepare(fs->tx_port, fs->tx_queue,
+		pkts_burst, nb_pkt);
+	if (unlikely(nb_prep != nb_pkt)) {
+		fprintf(stderr,
+			"Preparing packet burst to transmit failed: %s\n",
+			rte_strerror(rte_errno));
+		fs->fwd_dropped += (nb_pkt - nb_prep);
+		rte_pktmbuf_free_bulk(&pkts_burst[nb_prep], nb_pkt - nb_prep);
+	}
+
+	nb_tx = common_fwd_stream_transmit(fs, pkts_burst, nb_prep);
 
 	if (txonly_multi_flow)
 		RTE_PER_LCORE(_src_port_var) -= nb_pkt - nb_tx;
-- 
2.34.1