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

  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(-)
  

On Wed,  3 Jan 2024 09:29:12 +0800
Kaiwen Deng <kaiwenx.deng@intel.com> wrote:

>  
> -	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));

The main failure likely is mismatched offload flags, so it might be helpful
to print offload flags of that mbuf.

> +		fs->fwd_dropped += (nb_pkt - nb_prep);

Nit: no parenthesis needed here.

> +		rte_pktmbuf_free_bulk(&pkts_burst[nb_prep], nb_pkt - nb_prep);
> +	}
> +
> +	nb_tx = common_fwd_stream_transmit(fs, pkts_burst, nb_prep);
>
  

On Wed, Jan 3, 2024 at 7:38 AM Kaiwen Deng <kaiwenx.deng@intel.com> wrote:
>
> 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,

More performant version will be
to have two versions of fwd_engine.packet_fwd based on the offload.
And fix up the correct  tx_only_engine.packet_fwd at runtime based on
the offload selected.