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

[Hideyuki Yamashita <yamashita.hideyuki@po.ntt-tx.co.jp>]

Hi 

Thanks for your answering to my question.
Please see inline.
> Hi,  Hideyuki Yamashita
> 
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Hideyuki Yamashita
> > Sent: Wednesday, October 31, 2018 4:22 PM
> > To: dev@dpdk.org
> > Subject: [dpdk-dev] Question about jumbo frame support on ixgbe
> > 
> > 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?
> 
> Your understanding above correct, but 82599 and x550 has support jumbo frame receive by now!
> In order to use this feature on ixgbe, you need do the following steps:
> 
> 1. you must set dev_conf.rxmode. max_rx_pkt_len to a big number, eg. 9500, when doing port start, for example when start port in API rte_eth_dev_start().
> ixgbe_dev_rx_init() will chose a scatter receive function if the max_rx_pkt_len is larger than the mbuf size, you do not need to set DEV_RX_OFFLOAD_SCATTER bit in 
> dev_conf.rxmode.offloads, this is the work of PMD driver when it detect jumbo frame is needed to be supported.
Thanks for your info.

> 2. set dev_conf.txmode.offloads bit of  DEV_TX_OFFLOAD_MULTI_SEGS to 1 when doing rte_eth_tx_queue_setup() or , this is very important!! 
> If you not do this, you may only receive JUMBO frame but not forward out. Because as you say,
> the receive packets maybe has a mbuf chains(depending on the size relationship of mbuf size and the max_rx_pkt_len).
> But in ixgbe PMD for setting tx function, it is confusing  in ixgbe_set_tx_function(), you need  to take care of it, it is based on queue offloads bit!
What will happen if DEV_TX_OFFLOAD_MULTI_SEGS is set to 1.
Packets are sent fragmented or re-built as a Jumbo frame and sent to
network?
(My guess is former(packet will be sent fragmented though))

> 3. enable it using CLI "port config mtu <port_id> <value>" if you are using testpmd or using API rte_eth_dev_set_mtu() for your own APP.
> The mtu number is just what you need to update for a large number.
I want to know the relationship between 1,2 and 3.
Do I have to do all 3 steps to send/receive jumbo frame? 
Or, when I relalize jumbo frame support programatically execute 1 and 2,
if I do not modify program and just change setting via CLI then execute
3?

Thanks and BR,
Hideyuki Yamashita
NTT TechnoCross
 
> And all my discussion is based on pf port, if you are using vf, we can have a further discussion.
> Please feel free to contact me if necessary.
> 
> > 
> > BR,
> > Hideyuki Yamashita
> > NTT TechnoCross
>