Re: [dpdk-dev] [PATCH v4 3/5] net/ice: fix max mtu size packets with vlan tag cannot be received by default

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Yang, SteveX <stevex.yang@intel.com>
> Sent: Wednesday, September 30, 2020 9:32 AM
> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; dev@dpdk.org
> Cc: Zhao1, Wei <wei.zhao1@intel.com>; Guo, Jia <jia.guo@intel.com>; Yang,
> Qiming <qiming.yang@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>; Xing,
> Beilei <beilei.xing@intel.com>
> Subject: RE: [PATCH v4 3/5] net/ice: fix max mtu size packets with vlan tag
> cannot be received by default
> 
> 
> 
> > -----Original Message-----
> > From: Zhang, Qi Z <qi.z.zhang@intel.com>
> > Sent: Wednesday, September 30, 2020 8:35 AM
> > To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Yang, SteveX
> > <stevex.yang@intel.com>; dev@dpdk.org
> > Cc: Zhao1, Wei <wei.zhao1@intel.com>; Guo, Jia <jia.guo@intel.com>;
> > Yang, Qiming <qiming.yang@intel.com>; Wu, Jingjing
> > <jingjing.wu@intel.com>; Xing, Beilei <beilei.xing@intel.com>
> > Subject: RE: [PATCH v4 3/5] net/ice: fix max mtu size packets with
> > vlan tag cannot be received by default
> >
> >
> >
> > > -----Original Message-----
> > > From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> > > Sent: Wednesday, September 30, 2020 7:02 AM
> > > To: Zhang, Qi Z <qi.z.zhang@intel.com>; Yang, SteveX
> > > <stevex.yang@intel.com>; dev@dpdk.org
> > > Cc: Zhao1, Wei <wei.zhao1@intel.com>; Guo, Jia <jia.guo@intel.com>;
> > > Yang, Qiming <qiming.yang@intel.com>; Wu, Jingjing
> > > <jingjing.wu@intel.com>; Xing, Beilei <beilei.xing@intel.com>
> > > Subject: RE: [PATCH v4 3/5] net/ice: fix max mtu size packets with
> > > vlan tag cannot be received by default
> > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Yang, SteveX <stevex.yang@intel.com>
> > > > > Sent: Monday, September 28, 2020 2:56 PM
> > > > > To: dev@dpdk.org
> > > > > Cc: Zhao1, Wei <wei.zhao1@intel.com>; Guo, Jia
> > > > > <jia.guo@intel.com>; Yang, Qiming <qiming.yang@intel.com>;
> > > > > Zhang, Qi Z <qi.z.zhang@intel.com>; Wu, Jingjing
> > > > > <jingjing.wu@intel.com>; Xing, Beilei <beilei.xing@intel.com>;
> > > > > Ananyev, Konstantin <konstantin.ananyev@intel.com>; Yang, SteveX
> > > > > <stevex.yang@intel.com>
> > > > > Subject: [PATCH v4 3/5] net/ice: fix max mtu size packets with
> > > > > vlan tag cannot be received by default
> > > > >
> > > > > testpmd will initialize default max packet length to 1518 which
> > > > > doesn'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.
> > > > >
> > > > > ice can support dual vlan tags that need more 8 bytes for max
> > > > > packet size, so, configures the correct max packet size in
> > > > > dev_config
> > ops.
> > > > >
> > > > > Fixes: 50cc9d2a6e9d ("net/ice: fix max frame size")
> > > > >
> > > > > Signed-off-by: SteveX Yang <stevex.yang@intel.com>
> > > > > ---
> > > > >  drivers/net/ice/ice_ethdev.c | 11 +++++++++++
> > > > >  1 file changed, 11 insertions(+)
> > > > >
> > > > > diff --git a/drivers/net/ice/ice_ethdev.c
> > > > > b/drivers/net/ice/ice_ethdev.c index
> > > > > cfd357b05..6b7098444 100644
> > > > > --- a/drivers/net/ice/ice_ethdev.c
> > > > > +++ b/drivers/net/ice/ice_ethdev.c
> > > > > @@ -3146,6 +3146,7 @@ ice_dev_configure(struct rte_eth_dev *dev)
> > > > > struct ice_adapter *ad =
> > > > > ICE_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
> > > > >  struct ice_pf *pf =
> > > > > ICE_DEV_PRIVATE_TO_PF(dev->data->dev_private);
> > > > > +uint32_t frame_size = dev->data->mtu + ICE_ETH_OVERHEAD;
> > > > >  int ret;
> > > > >
> > > > >  /* Initialize to TRUE. If any of Rx queues doesn't meet the @@
> > > > > -3157,6
> > > > > +3158,16 @@ ice_dev_configure(struct rte_eth_dev *dev)
> > > > >  if (dev->data->dev_conf.rxmode.mq_mode & ETH_MQ_RX_RSS_FLAG)
> > > > > dev->data->dev_conf.rxmode.offloads |=
> > DEV_RX_OFFLOAD_RSS_HASH;
> > > > >
> > > > > +/**
> > > > > + * Considering QinQ packet, max frame size should be equal or
> > > > > + * larger than total size of MTU and Ether overhead.
> > > > > + */
> > > >
> > > > > +if (frame_size > dev->data->dev_conf.rxmode.max_rx_pkt_len) {
> > > >
> > > >
> > > > Why we need this check?
> > > > Can we just call ice_mtu_set directly
> > >
> > > I think that without that check we can silently overwrite provided
> > > by user dev_conf.rxmode.max_rx_pkt_len value.
> >
> > OK, I see
> >
> > But still have one question
> > dev->data->mtu is initialized to 1518 as default , but if application
> > dev->data->set
> > dev_conf.rxmode.max_rx_pkt_len = 1000 in dev_configure.
> > does that mean we will still will set mtu to 1518, is this expected?
> >
> 
> max_rx_pkt_len should be larger than mtu at least, so we should raise the
> max_rx_pkt_len (e.g.:1518) to hold expected mtu value (e.g.: 1500).

Ok, this describe the problem more general and better to replace exist code comment and commit log for easy understanding.
Please send a new version for reword


> Generally, the mtu value can be adjustable from user (e.g.: ip link set ens801f0
> mtu 1400), hence, we just adjust the max_rx_pkt_len to satisfy mtu
> requirement.
> 
> > Should we just call ice_mtu_set(dev, dev_conf.rxmode.max_rx_pkt_len)
> > here?
> ice_mtu_set(dev, mtu) will append ether overhead to
> frame_size/max_rx_pkt_len, so we need pass the mtu value as the 2nd
> parameter, or not the max_rx_pkt_len.
> 
> >
> >
> > >
> > > > And please remove above comment, since ether overhead is already
> > > considered in ice_mtu_set.
> Ether overhead is already considered in ice_mtu_set, but it also should be
> considered as the adjustment condition that if ice_mtu_set need be invoked.
> So, it perhaps should remain this comment before this if() condition.
> 
> > > >
> > > >
> > > > > +ret = ice_mtu_set(dev, dev->data->mtu); if (ret != 0) return
> > > > > +ret; }
> > > > > +
> > > > >  ret = ice_init_rss(pf);
> > > > >  if (ret) {
> > > > >  PMD_DRV_LOG(ERR, "Failed to enable rss for PF");
> > > > > --
> > > > > 2.17.1
> > > >
> > >
> >
>