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

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Date:   Tue, 29 Oct 2019 14:59:05 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Haiyang Zhang <haiyangz@...rosoft.com>
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

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.