Re: [dpdk-dev] [PATCH v8 1/2] app/testpmd: fix max rx packet length for VLAN packets

[Thomas Monjalon <thomas@monjalon.net>]

+ more maintainers Cc'ed

We have a critical issue with testpmd in -rc2.
It is blocking a lot of testing.
Would be good to do a -rc3 today.
Please see below.

05/11/2020 11:44, Thomas Monjalon:
> 05/11/2020 11:37, Ferruh Yigit:
> > On 11/5/2020 9:33 AM, Yang, SteveX wrote:
> > > From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> > >> Sent: Thursday, November 5, 2020 4:54 PM
> > >> To: Thomas Monjalon <thomas@monjalon.net>; Yang, SteveX
> > >> <stevex.yang@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>
> > >> Cc: dev@dpdk.org; Ananyev, Konstantin <konstantin.ananyev@intel.com>;
> > >> Xing, Beilei <beilei.xing@intel.com>; Lu, Wenzhuo <wenzhuo.lu@intel.com>;
> > >> Iremonger, Bernard <bernard.iremonger@intel.com>; Yang, Qiming
> > >> <qiming.yang@intel.com>; mdr@ashroe.eu; nhorman@tuxdriver.com;
> > >> david.marchand@redhat.com
> > >> Subject: Re: [dpdk-dev] [PATCH v8 1/2] app/testpmd: fix max rx packet
> > >> length for VLAN packets
> > >>
> > >> On 11/4/20 11:39 PM, Thomas Monjalon wrote:
> > >>> 04/11/2020 21:19, Ferruh Yigit:
> > >>>> On 11/4/2020 5:55 PM, Thomas Monjalon wrote:
> > >>>>> 04/11/2020 18:07, Ferruh Yigit:
> > >>>>>> On 11/4/2020 4:51 PM, Thomas Monjalon wrote:
> > >>>>>>> 03/11/2020 14:29, Ferruh Yigit:
> > >>>>>>>> On 11/2/2020 11:48 AM, Ferruh Yigit wrote:
> > >>>>>>>>> On 11/2/2020 8:52 AM, SteveX Yang wrote:
> > >>>>>>>>>> When the max rx packet length is smaller than the sum of mtu
> > >>>>>>>>>> size and ether overhead size, it should be enlarged, otherwise
> > >>>>>>>>>> the VLAN packets will be dropped.
> > >>>>>>>>>>
> > >>>>>>>>>> Fixes: 35b2d13fd6fd ("net: add rte prefix to ether defines")
> > >>>>>>>>>>
> > >>>>>>>>>> Signed-off-by: SteveX Yang <stevex.yang@intel.com>
> > >>>>>>>>>
> > >>>>>>>>> Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
> > >>>>>>>>
> > >>>>>>>> Applied to dpdk-next-net/main, thanks.
> > >>>>>>>>
> > >>>>>>>> only 1/2 applied since discussion is going on for 2/2.
> > >>>>>>>
> > >>>>>>> I'm not sure this testpmd change is good.
> > >>>>>>>
> > >>>>>>> Reminder: testpmd is for testing the PMDs.
> > >>>>>>> Don't we want to see VLAN packets dropped in the case described
> > >> above?
> > >>>>>>>
> > >>>>>>
> > >>>>>> The patch set 'max_rx_pkt_len' in a way to make MTU 1500 for all
> > >>>>>> PMDs, otherwise testpmd set hard-coded 'RTE_ETHER_MAX_LEN'
> > >> value,
> > >>>>>> which makes MTU between 1492-1500 depending on PMD.
> > >>>>>>
> > >>>>>> It is application responsibility to provide correct 'max_rx_pkt_len'.
> > >>>>>> I guess the original intention was to set MTU as 1500 but was not
> > >>>>>> correct for all PMDs and this patch is fixing it.
> > >>>>>>
> > >>>>>> The same problem in the ethdev, (assuming 'RTE_ETHER_MAX_LEN'
> > >> will
> > >>>>>> give MTU 1500), the other patch in the set is to fix it later.
> > >>>>>
> > >>>>> OK but the testpmd patch is just hiding the issue, isn't it?
> > >>>>>
> > >>>>
> > >>>> I don't think so, issue was application (testpmd) setting the
> > >> 'max_rx_pkt_len'
> > >>>> wrong.
> > >>>>
> > >>>> What is hidden?
> > >>>
> > >>> I was looking for adding a helper in ethdev API.
> > >>> But I think I can agree with your way of thinking.
> > >>>
> > >>
> > >> The patch breaks running testpmd on Virtio-Net because the driver
> > >> populates dev_info.max_rx_pktlen but keeps dev_info.max_mtu equal to
> > >> UINT16_MAX as it was filled in by ethdev. As the result:
> > >>
> > >> Ethdev port_id=0 max_rx_pkt_len 11229 > max valid value 9728 Fail to
> > >> configure port 0
> > > 
> > > Similar issue occurred for other net PMD drivers which use default max_mtu (UINT16_MAX).
> > > More strict checking condition will be added within new patch sooner.
> > > 
> > 
> > :(
> > 
> > For drivers not providing 'max_mtu' information explicitly, the default 
> > 'UINT16_MAX' is set in ethdev layer.
> > This prevents calculating PMD specific 'overhead' and the logic in the patch is 
> > broken.
> > 
> > Indeed this makes inconsistency in the driver too, for example for virtio, it 
> > claims 'max_rx_pktlen' as "VIRTIO_MAX_RX_PKTLEN (9728)" and 'max_mtu' as 
> > UINT16_MAX. From 'virtio_mtu_set()' we can see the real limit is 
> > 'VIRTIO_MAX_RX_PKTLEN'.
> > 
> > When PMDs fixed, the logic in this patch can work but not sure if post -rc2 is 
> > good time to start fixing the PMDs.
> 
> Do you suggest revert is the best choice here?