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

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

> -----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. 

> 
> 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

> 
> Tom has more details. But you can reproduce problem by just testing current
> code with the transparent VLAN option.
> 
>