linux-kernel - Re: [PATCH 2/4] virtio-net: add support of UDP segmentation (USO) on the host

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Date:   Tue, 11 May 2021 11:23:50 +0300
From:   Yuri Benditovich <yuri.benditovich@...nix.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Yan Vugenfirer <yan@...nix.com>
Subject: Re: [PATCH 2/4] virtio-net: add support of UDP segmentation (USO) on
 the host

On Tue, May 11, 2021 at 9:47 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 在 2021/5/11 下午12:42, Yuri Benditovich 写道:
> > Large UDP packet provided by the guest with GSO type set to
> > VIRTIO_NET_HDR_GSO_UDP_L4 will be divided to several UDP
> > packets according to the gso_size field.
> >
> > Signed-off-by: Yuri Benditovich <yuri.benditovich@...nix.com>
> > ---
> >   include/linux/virtio_net.h | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> > index b465f8f3e554..4ecf9a1ca912 100644
> > --- a/include/linux/virtio_net.h
> > +++ b/include/linux/virtio_net.h
> > @@ -51,6 +51,11 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
> >                       ip_proto = IPPROTO_UDP;
> >                       thlen = sizeof(struct udphdr);
> >                       break;
> > +             case VIRTIO_NET_HDR_GSO_UDP_L4:
> > +                     gso_type = SKB_GSO_UDP_L4;
> > +                     ip_proto = IPPROTO_UDP;
> > +                     thlen = sizeof(struct udphdr);
> > +                     break;
>
>
> This is only for rx, how about tx?

In terms of the guest this is only for TX.
Guest RX is a different thing, this is actually coalescing of
segmented UDP packets into a large one.
This feature is not defined in the virtio spec yet and the support of
it first of all depends on the OS.
For example: TCP LSO (guest TX) is supported almost by all the
versions of Windows.
TCP RSC (coalescing of TCP segments) is supported by Win 8 / Server 2012 and up.
UDP segmentation is supported by Windows kernels 1903+
UDP coalescing is defined by Windows kernels 2004+ and not supported
by the driver yet.

>
> Thanks
>
>
>
> >               default:
> >                       return -EINVAL;
> >               }
>