On Wed, 3 Jan 2024 09:29:12 +0800
Kaiwen Deng <kaiwenx.d...@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: sta...@dpdk.org
>
> Signed-off-by: Kaiwen Deng <kaiwenx.d...@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);
The comment section on this patch raises lots of good points.
1. Testpmd and example applications are not calling tx_prepare.
2. Testpmd and examples are not checking descriptor limits.
3. It is not clear from documentation when tx_prepare is required.
On a practical level, if testpmd was being used in txonly mode,
if the condition ever triggered, you really really don't want to
print a message there since it would likely be endless stream of messages.
Please consider the comments and come back with a better solution in v2.
