RE: [PATCH net-next, 3/4] hv_netvsc: Add XDP support

[Haiyang Zhang <haiyangz@microsoft.com>]

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Tuesday, October 29, 2019 5:59 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: Jakub Kicinski <jakub.kicinski@netronome.com>; sashal@kernel.org;
> linux-hyperv@vger.kernel.org; netdev@vger.kernel.org; KY Srinivasan
> <kys@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> olaf@aepfle.de; vkuznets <vkuznets@redhat.com>; davem@davemloft.net;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH net-next, 3/4] hv_netvsc: Add XDP support
> 
> On Tue, 29 Oct 2019 19:17:25 +0000
> Haiyang Zhang <haiyangz@microsoft.com> wrote:
> 
> > > -----Original Message-----
> > > From: Jakub Kicinski <jakub.kicinski@netronome.com>
> > > Sent: Monday, October 28, 2019 5:33 PM
> > > To: Haiyang Zhang <haiyangz@microsoft.com>
> > > Cc: sashal@kernel.org; linux-hyperv@vger.kernel.org;
> > > netdev@vger.kernel.org; KY Srinivasan <kys@microsoft.com>; Stephen
> > > Hemminger <sthemmin@microsoft.com>; olaf@aepfle.de; vkuznets
> > > <vkuznets@redhat.com>; davem@davemloft.net; linux-
> > > kernel@vger.kernel.org
> > > Subject: Re: [PATCH net-next, 3/4] hv_netvsc: Add XDP support
> > >
> > > On Mon, 28 Oct 2019 21:07:04 +0000, Haiyang Zhang wrote:
> > > > This patch adds support of XDP in native mode for hv_netvsc driver,
> and
> > > > transparently sets the XDP program on the associated VF NIC as well.
> > > >
> > > > XDP program cannot run with LRO (RSC) enabled, so you need to
> disable
> > > LRO
> > > > before running XDP:
> > > >         ethtool -K eth0 lro off
> > > >
> > > > XDP actions not yet supported:
> > > >         XDP_TX, XDP_REDIRECT
> > >
> > > I don't think we want to merge support without at least XDP_TX these
> > > days..
> > Thanks for your detailed comments --
> > I'm working on the XDP_TX...
> >
> > >
> > > And without the ability to prepend headers this may be the least
> > > complete initial XDP implementation we've seen :(
> > The RNDIS packet buffer received by netvsc doesn't have a head room, but
> I'm
> > considering copy the packets to the page buffer, with a head room space
> > reserved for XDP.
> 
> 
> There is a small amount of headroom available by reusing the RNDIS
> header and packet space. Looks like 40 bytes or so.
Yes, I thought about the RNDIS header. But is this space sufficient?
I saw some drivers, like virtio_net gives bigger headroom: 256 bytes.

Thanks,
- Haiyang