Re: [dpdk-dev] Question about jumbo frame support on ixgbe

["Zhao1, Wei" <wei.zhao1@intel.com>]

Hi,  Stephen Hemminger

> -----Original Message-----
> From: Zhao1, Wei
> Sent: Thursday, November 1, 2018 11:27 AM
> To: 'Stephen Hemminger' <stephen@networkplumber.org>; Hideyuki
> Yamashita <yamashita.hideyuki@po.ntt-tx.co.jp>
> Cc: dev@dpdk.org
> Subject: RE: [dpdk-dev] Question about jumbo frame support on ixgbe
> 
> 
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen
> Hemminger
> > Sent: Wednesday, October 31, 2018 11:49 PM
> > To: Hideyuki Yamashita <yamashita.hideyuki@po.ntt-tx.co.jp>
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] Question about jumbo frame support on ixgbe
> >
> > On Wed, 31 Oct 2018 17:22:02 +0900
> > Hideyuki Yamashita <yamashita.hideyuki@po.ntt-tx.co.jp> wrote:
> >
> > > Hi,
> > >
> > > I have a very basic question about jumbo frame support for ixgbe.
> > >
> > > I understand that some drivers support jumbo frame and if it receive
> > > jumbo packet (greater than 1500 byte), it creates mbuf chains and
> > > pass it to DPDK application through e.g. rte_eth_rx_burst.
> > >
> > > However it looks that ixgbe driver does not support jumbo frame.
> > >
> > > Q1. Is my understanding above correct?
> > > Q2. If A1 equals YES, then are there any future plan to support
> > > jumbo frame on ixgbe?
> > >
> > > BR,
> > > Hideyuki Yamashita
> > > NTT TechnoCross
> > >
> >
> > I don't work for Intel, and haven't tried jumbo frames on ixgbe.
> > The hardware does support jumbo frames.
> > You might be confusing the overlapping receive offload values.
> >
> > The setting for using jumbo frames is in current DPDK is shown as
> > available in device as:
> > 	rx_offload_capa & DEV_RX_OFFLOAD_JUMBO_FRAME In order to
> use it, this
> > bit must be setn in rx_conf that is passed to rte_eth_rx_queue_setup
> >
> 
> Yes,
> dev_conf.rxmode.offloads bits of DEV_RX_OFFLOAD_JUMBO_FRAME
> should be set to 1 when start port in API rte_eth_dev_start().
> IF you are using testpmd  APP, you should set struct rte_eth_rxmode
> rx_mode  offloads bits of DEV_RX_OFFLOAD_JUMBO_FRAME.
>  but  I think only set this bit of DEV_RX_OFFLOAD_JUMBO_FRAME is not
> sufficient for enable this jumbo frame feature, Because in PMD code, this
> flag do not set bit of  IXGBE_HLREG0_JUMBOEN in register IXGBE_HLREG0, I
> think this is something We need update.

Correct some content above, set this bit of DEV_RX_OFFLOAD_JUMBO_FRAME can 
result in set bit of  IXGBE_HLREG0_JUMBOEN in register IXGBE_HLREG0,  but it still need some check of 
packet size boundary for code safe!

> 
> >
> > The feature bit that creates multiple mbuf's if necessary on receive is:
> > 	rx_offload_capa  & DEV_RX_OFFLOAD_SCATTER Likewise to enable it,
> this
> > must be set in rte_eth_rx_queue_setup rx_conf.
> >
> >
> 
> Yes, this step can chose scatter rx function for PMD, but not MUST, details of
> discussion for this is in other mail.
> https://mails.dpdk.org/archives/dev/2018-November/117771.html

After a double check of code, I am sure DEV_RX_OFFLOAD_SCATTER is not a must choice, it is depend on 
the relationship of max_rx_pkt_len and mbuf size, for example you set  max_rx_pkt_len to 9.5k and mbuf size to 2048,
of course we need to using scatter receiving mode.

> 
> 
>