RE: [PATCH v2] examples/l3fwd: fix jumbo packet drop issue

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> From: Rohit Raj <rohit.raj@nxp.com>
> 
> l3fwd uses mbufs with 2KB data size. If we enable jumbo packets, it is
> not able to store packets with size greater than 2KB, hence these
> packets are dropped.
> 
> This patch fixes this issue by enabling scatter for jumbo packet, if
> it is supported by NIC.
> 
> If scatter is not supported by NIC and max packet length is greater
> than default mbuf data size, then application exits with proper error
> message.
> 
> Fixes: f68aad7904f ("examples/l3fwd: update")
> 
> Signed-off-by: Rohit Raj <rohit.raj@nxp.com>
> Signed-off-by: Sachin Saxena <sachin.saxena@nxp.com>
> Signed-off-by: Vanshika Shukla <vanshika.shukla@nxp.com>
> ---
> 
> v2:
> * Improved the check to not enable Rx scatter when packets fits into
>   buffer.
> * Check if jumbo packet is enabled using max_rx_pktlen instead of
>   jumbo packet flag.
> 
>  examples/l3fwd/main.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/examples/l3fwd/main.c b/examples/l3fwd/main.c
> index d69373f881..61448c759c 100644
> --- a/examples/l3fwd/main.c
> +++ b/examples/l3fwd/main.c
> @@ -1109,6 +1109,19 @@ l3fwd_poll_resource_setup(void)
>  				"Invalid max packet length: %u (port %u)\n",
>  				max_pkt_len, portid);
> 
> +		/* Enable Receive side SCATTER, if supported by NIC,
> +		 * when jumbo packet is enabled.
> +		 */


From the code below, it looks like you always enable scatter if HW supports it.
Without paying attention to max_pkt_len provided by user. 

> +		if (dev_info.max_rx_pktlen > RTE_MBUF_DEFAULT_DATAROOM) {
> +			if (dev_info.rx_offload_capa &
> +			    RTE_ETH_RX_OFFLOAD_SCATTER)
> +				local_port_conf.rxmode.offloads |=
> +						RTE_ETH_RX_OFFLOAD_SCATTER;
> +			else
> +				rte_exit(EXIT_FAILURE,
> +					 "Max packet length greater than default MBUF size\n");
> +		}
> +
>  		if (dev_info.tx_offload_capa & RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE)
>  			local_port_conf.txmode.offloads |=
>  				RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE;
> --
> 2.17.1