Re: [dpdk-dev] [PATCH] ixgbe: Discard SRIOV transparent vlan packet headers.

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 14 Dec 2015 19:57:10 +0000
"Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:

> 
> 
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Monday, December 14, 2015 7:25 PM
> > To: Ananyev, Konstantin
> > Cc: Zhang, Helin; dev@dpdk.org; Tom Kiely
> > Subject: Re: [PATCH] ixgbe: Discard SRIOV transparent vlan packet headers.
> > 
> > On Mon, 14 Dec 2015 19:12:26 +0000
> > "Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:
> > 
> > >
> > >
> > > > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > > > Sent: Friday, December 11, 2015 4:59 PM
> > > > To: Zhang, Helin; Ananyev, Konstantin
> > > > Cc: dev@dpdk.org; Tom Kiely; Stephen Hemminger
> > > > Subject: [PATCH] ixgbe: Discard SRIOV transparent vlan packet headers.
> > > >
> > > > From: Tom Kiely <tkiely@brocade.com>
> > > >
> > > > SRIOV VFs support "transparent" vlans. Traffic from/to a VM
> > > > associated with a VF is tagged/untagged with the specified
> > > > vlan in a manner intended to be totally transparent to the VM.
> > > >
> > > > The vlan is specified by "ip link set <device> vf <n> vlan <v>".
> > > > The VM is not configured for any vlan on the VF and the VM
> > > > should never see these transparent vlan headers for that reason.
> > > >
> > > > However, in practice these vlan headers are being received by
> > > > the VM which discards the packets as that vlan is unknown to it.
> > > > The Linux kernel explicitly discards such vlan headers but DPDK
> > > > does not.
> > > > This patch mirrors the kernel behaviour for SRIOV VFs only
> > >
> > >
> > > I have few concerns about that approach:
> > >
> > > 1. I don't think vlan_tci info should *always* be stripped by vf RX routine.
> > > There could be configurations when that information might be needed by upper layer.
> > > Let say VF can be member of 2 or more VLANs and upper layer would like to have that information
> > > for further processing.
> > > Or special mirror VF, that does traffic snnoping, or something else.
> > > 2. Proposed implementation would introduce a slowdown for all VF RX routines.
> > > 3. From the description it seems like the aim is to clear VLAN information for the RX packet.
> > > Though the patch actually clears VLAN info only for the RX packet whose VLAN tag is not present inside SW copy of VFTA table.
> > > Which makes no much point to me:
> > > If VLAN is not present in HW VFTA table, then packet with that VLAN tag will be discarded by HW anyway.
> > > If it is present inside VFTA table (both SW & HW), then VLAN information would be preserved with and without the patch.
> > >
> > > If you need to clear VLAN information, why not to do it on the upper layer - inside your application itself?
> > > Either create some sort of wrapper around rx_burst(), or setup an RX call-back for your VF device.
> > >
> > > Konstantin
> > 
> > 
> > The aim is to get SRIOV to work when the transparent VLAN tag feature is used.
> > Please talk to the Linux driver team. Similar code exists there in ixgbevf_process_skb_fields.
> 
> 
> Ah ok, I realised what you are trying to achieve now:
> You setup HW VFTA[] from the PF, so from VF point of view SW copy of the VFTA[] remains unset.
> So HW will pass VLAN packet in, but then SW will clear VLAN tag.
> Ok, that clears #3 above, but I think #1,2 still remain. 

On the host, what configured is a vlan tag per VF per guest

Tom had more info in the original mail.

http://permalink.gmane.org/gmane.comp.networking.dpdk.devel/28932

> > 
> > The other option is have a copy of all the receive logic which is only
> > used by VF code.
> 
> Why that's the only option?
> Why can't you clear that VLAN information above the PMD layer?
> Keep/obtain a copy of VFTA[] somewhere on the upper layer,
> and do actual clear after rx_burst() returns?
> Konstantin

The problem is that the guest is supposed to not see the VLAN tags (it has no reason to),
but the hardware leaves a VLAN tag on there.