[dpdk-dev] [PATCH v1] examples/l3fwd: fix jumbo packet drop issue

[Ferruh Yigit]

On 7/27/2021 10:25 AM, rohit.raj at nxp.com wrote:
> From: Rohit Raj <rohit.raj at 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 jumbo 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 at nxp.com>
> Signed-off-by: Sachin Saxena <sachin.saxena at nxp.com>
> Signed-off-by: Vanshika Shukla <vanshika.shukla at nxp.com>
> ---
>  examples/l3fwd/main.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/examples/l3fwd/main.c b/examples/l3fwd/main.c
> index 4cb800aa15..6aaaa8ecb5 100644
> --- a/examples/l3fwd/main.c
> +++ b/examples/l3fwd/main.c
> @@ -1035,6 +1035,20 @@ l3fwd_poll_resource_setup(void)
>  				"Error during getting device (port %u) info: %s\n",
>  				portid, strerror(-ret));
>  
> +		/* Enable Receive side SCATTER, if supported by NIC,
> +		 * when jumbo packet is enabled.
> +		 */
> +		if (local_port_conf.rxmode.offloads &
> +				DEV_RX_OFFLOAD_JUMBO_FRAME){
> +			if (dev_info.rx_offload_capa & DEV_RX_OFFLOAD_SCATTER)
> +				local_port_conf.rxmode.offloads |=
> +						DEV_RX_OFFLOAD_SCATTER;
> +			else if (local_port_conf.rxmode.max_rx_pkt_len >
> +					RTE_MBUF_DEFAULT_DATAROOM)
> +				rte_exit(EXIT_FAILURE,
> +					"Max packet length greater than default MBUF size\n");

This is a configuration set by application. So application is failing itself
because of configuration it sets, seems odd.

I guess the jumbo frame can be enabled when user provides '--enable-jumbo'
argument. What do you think adding above check where that argument is parsed.

Btw, no need to enable scattered Rx if the packets fits into buffer, so above
check can be done slightly different:

if (max_rx_pkt_len > buffer_size)
	if (OFFLOAD_SCATTER supported)
		enable OFFLOAD_SCATTER
	else
		fail


> +		}
> +
>  		if (dev_info.tx_offload_capa & DEV_TX_OFFLOAD_MBUF_FAST_FREE)
>  			local_port_conf.txmode.offloads |=
>  				DEV_TX_OFFLOAD_MBUF_FAST_FREE;
>