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

[Rohit Raj <rohit.raj@nxp.com>]

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> Sent: Wednesday, August 11, 2021 5:01 PM
> To: Rohit Raj <rohit.raj@nxp.com>
> Cc: dev@dpdk.org; Nipun Gupta <nipun.gupta@nxp.com>; Hemant Agrawal
> <hemant.agrawal@nxp.com>; Sachin Saxena <sachin.saxena@nxp.com>;
> Vanshika Shukla <vanshika.shukla@nxp.com>
> Subject: Re: [dpdk-dev] [PATCH v1] examples/l3fwd: fix jumbo packet drop
> issue
> 
> On 7/27/2021 10:25 AM, rohit.raj@nxp.com wrote:
> > 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 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@nxp.com>
> > Signed-off-by: Sachin Saxena <sachin.saxena@nxp.com>
> > Signed-off-by: Vanshika Shukla <vanshika.shukla@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. 

We need to check if hardware supports Rx scatter. To do this, we need to get Rx
capability. Hence, this is a better place to perform this check.

>
> 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

Agreed. I will do this in next version of the patch.

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