netdev - RE: [PATCH net-next, 3/4] hv

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Message-ID: <DM6PR21MB13378821FCD94A4D342079DBCA610@DM6PR21MB1337.namprd21.prod.outlook.com>
Date:   Tue, 29 Oct 2019 22:08:26 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
CC:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next, 3/4] hv_netvsc: Add XDP support



> -----Original Message-----
> From: Stephen Hemminger <stephen@...workplumber.org>
> Sent: Tuesday, October 29, 2019 5:59 PM
> To: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Jakub Kicinski <jakub.kicinski@...ronome.com>; sashal@...nel.org;
> linux-hyperv@...r.kernel.org; netdev@...r.kernel.org; KY Srinivasan
> <kys@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>;
> olaf@...fle.de; vkuznets <vkuznets@...hat.com>; davem@...emloft.net;
> linux-kernel@...r.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@...rosoft.com> wrote:
> 
> > > -----Original Message-----
> > > From: Jakub Kicinski <jakub.kicinski@...ronome.com>
> > > Sent: Monday, October 28, 2019 5:33 PM
> > > To: Haiyang Zhang <haiyangz@...rosoft.com>
> > > Cc: sashal@...nel.org; linux-hyperv@...r.kernel.org;
> > > netdev@...r.kernel.org; KY Srinivasan <kys@...rosoft.com>; Stephen
> > > Hemminger <sthemmin@...rosoft.com>; olaf@...fle.de; vkuznets
> > > <vkuznets@...hat.com>; davem@...emloft.net; linux-
> > > kernel@...r.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