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

[Jerin Jacob <jerinjacobk@gmail.com>]

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.