Re: [dpdk-dev] [PATCH v1 5/5] net/i40e: fix max mtu size packets with vlan tag cannot be received by default

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

> > Subject: RE: [dpdk-dev] [PATCH v1 5/5] net/i40e: fix max mtu size packets
> > with vlan tag cannot be received by default
> >
> > > testpmd will initialize default max packet length to 1518 which does't
> > > include vlan tag size in ether overheader. Once, send the max mtu
> > > length packet with vlan tag, the max packet length will exceed 1518
> > > that will cause packets dropped directly from NIC hw side. But for
> > > i40e/i40evf, they should support dual vlan tags that need more 8 bytes
> > > for max packet size, so, configure the correct max packet size in dev_config
> > ops.
> > >
> > > Fixes: ff8282f4bbcd ("net/i40e: consider QinQ when setting MTU")
> > >
> > > Signed-off-by: SteveX Yang <stevex.yang@intel.com>
> > > ---
> > >  drivers/net/i40e/i40e_ethdev.c    | 10 ++++++++++
> > >  drivers/net/i40e/i40e_ethdev_vf.c | 11 +++++++++++
> > >  2 files changed, 21 insertions(+)
> > >
> > > diff --git a/drivers/net/i40e/i40e_ethdev.c
> > > b/drivers/net/i40e/i40e_ethdev.c index 841447228..787ff61c0 100644
> > > --- a/drivers/net/i40e/i40e_ethdev.c
> > > +++ b/drivers/net/i40e/i40e_ethdev.c
> > > @@ -1917,6 +1917,7 @@ i40e_dev_configure(struct rte_eth_dev *dev)
> > >  	struct i40e_hw *hw = I40E_DEV_PRIVATE_TO_HW(dev->data-
> > >dev_private);
> > >  	enum rte_eth_rx_mq_mode mq_mode = dev->data-
> > >dev_conf.rxmode.mq_mode;
> > >  	int i, ret;
> > > +	struct rte_eth_rxmode *rxmode = &dev->data->dev_conf.rxmode;
> > >
> > >  	ret = i40e_dev_sync_phy_type(hw);
> > >  	if (ret)
> > > @@ -1930,6 +1931,15 @@ i40e_dev_configure(struct rte_eth_dev *dev)
> > >  	ad->tx_simple_allowed = true;
> > >  	ad->tx_vec_allowed = true;
> > >
> > > +	/* Considering QinQ packet, max frame size should be MTU and
> > > +	 * corresponding ether overhead.
> > > +	 */
> > > +	if (dev->data->mtu == RTE_ETHER_MTU &&
> > > +		rxmode->max_rx_pkt_len == RTE_ETHER_MAX_LEN) {
> >
> > Wonder why that particular max_rx_pkt_len and mtu values are important?
> > Shouldn't we always do here same calculations as we do in
> > i40e_dev_mtu_set()?
> 
> The combination of RTE_ETHER_MTU (1500) & RTE_ETHER_MAX_LEN (1518) is
> the generical default value from test-pmd or other apps. the RTE_ETHER_MAX_LEN
> doesn't include VLAN tag(s) size, hence, only need adjust frame size to hold real mtu
> size packet for the particular condition.

Ok, but user can overwrite default values in dev_configure.
What would happen if user would set rxmode.max_rx_pkt_len to RTE_ETHER_MAX_LEN + 1
or RTE_ETHER_MAX_LEN - 1?

> 
> >
> >
> > > +		rxmode->max_rx_pkt_len = RTE_ETHER_MTU +
> > I40E_ETH_OVERHEAD;
> > > +		rxmode->offloads |= DEV_RX_OFFLOAD_JUMBO_FRAME;
> > > +	}
> > > +
> > >  	if (dev->data->dev_conf.rxmode.mq_mode &
> > ETH_MQ_RX_RSS_FLAG)
> > >  		dev->data->dev_conf.rxmode.offloads |=
> > DEV_RX_OFFLOAD_RSS_HASH;
> > >
> > > diff --git a/drivers/net/i40e/i40e_ethdev_vf.c
> > > b/drivers/net/i40e/i40e_ethdev_vf.c
> > > index b755350cd..7410563db 100644
> > > --- a/drivers/net/i40e/i40e_ethdev_vf.c
> > > +++ b/drivers/net/i40e/i40e_ethdev_vf.c
> > > @@ -1669,6 +1669,7 @@ i40evf_dev_configure(struct rte_eth_dev *dev)
> > >  		I40E_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
> > >  	uint16_t num_queue_pairs = RTE_MAX(dev->data->nb_rx_queues,
> > >  				dev->data->nb_tx_queues);
> > > +	struct rte_eth_rxmode *rxmode = &dev->data->dev_conf.rxmode;
> > >
> > >  	/* Initialize to TRUE. If any of Rx queues doesn't meet the bulk
> > >  	 * allocation or vector Rx preconditions we will reset it.
> > > @@ -1681,6 +1682,16 @@ i40evf_dev_configure(struct rte_eth_dev *dev)
> > >  	dev->data->dev_conf.intr_conf.lsc =
> > >  		!!(dev->data->dev_flags & RTE_ETH_DEV_INTR_LSC);
> > >
> > > +
> > > +	/* Considering QinQ packet, max frame size should be MTU and
> > > +	 * corresponding ether overhead.
> > > +	 */
> > > +	if (dev->data->mtu == RTE_ETHER_MTU &&
> > > +		rxmode->max_rx_pkt_len == RTE_ETHER_MAX_LEN) {
> > > +		rxmode->max_rx_pkt_len = RTE_ETHER_MTU +
> > I40E_ETH_OVERHEAD;
> > > +		rxmode->offloads |= DEV_RX_OFFLOAD_JUMBO_FRAME;
> > > +	}
> > > +
> > >  	if (num_queue_pairs > vf->vsi_res->num_queue_pairs) {
> > >  		struct i40e_hw *hw;
> > >  		int ret;
> > > --
> > > 2.17.1