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Subject: Re: [virtio-comment] [PATCH 1/2] virtio-net: Fix receive buffer size calculation text
On Wed, 13 Dec 2023 12:28:48 +0200, Yuri Benditovich <yuri.benditovich@daynix.com> wrote:
> On Wed, Dec 13, 2023 at 8:44âAM Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> wrote:
>
> > On Fri, 10 Nov 2023 14:40:39 +0200, Parav Pandit <parav@nvidia.com> wrote:
> > > Receive buffer size calculation is based on the following
> > > negotiated features.
> > >
> > > The text has wrong calculation for IPv6 and also it has missed
> > > VIRTIO_NET_F_HASH_REPORT.
> > >
> > > The problem of igorance of VIRTIO_NET_F_HASH_REPORT is reported
> > > in [1], however fix for ipv6 payload length must also be
> > > considered.
> > >
> > > Since for the both the fixes touching same requirements, a
> > > new issue is created as [2].
> > >
> > > This patch brings following fixes.
> > >
> > > 1. Fix annotating struct virtio_net_hdr as field
> > > 2. Fix receive buffer calculation for guest GSO cases to consider
> > > ipv6 payload length
> > > 3. small grammar corrections for article
> > > 4. reword the requirement to consider the virtio_ndr_hdr which is
> > > depends on the negotiated feature, hence first clarify the
> > > struct virtio_net_hdr size
> > >
> > > [1] https://github.com/oasis-tcs/virtio-spec/issues/170
> > > [2] https://github.com/oasis-tcs/virtio-spec/issues/183
> > >
> > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/170
> > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/183
> > > Signed-off-by: Parav Pandit <parav@nvidia.com>
> > > ---
> > > device-types/net/description.tex | 25 ++++++++++++++++++-------
> > > 1 file changed, 18 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/device-types/net/description.tex
> > b/device-types/net/description.tex
> > > index 96f7dc5..f5647d4 100644
> > > --- a/device-types/net/description.tex
> > > +++ b/device-types/net/description.tex
> > > @@ -660,24 +660,35 @@ \subsubsection{Setting Up Receive
> > Buffers}\label{sec:Device Types / Network Devi
> > > If the VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
> > > VIRTIO_NET_F_GUEST_UFO, VIRTIO_NET_F_GUEST_USO4 or
> > VIRTIO_NET_F_GUEST_USO6
> > > features are used, the maximum incoming packet
> > > -will be to 65550 bytes long (the maximum size of a
> > > -TCP or UDP packet, plus the 14 byte ethernet header), otherwise
> > > -1514 bytes. The 12-byte struct virtio_net_hdr is prepended to this,
> > > -making for 65562 or 1526 bytes.
> > > +will of size 65589 bytes long (14 bytes of Ethernet header, plus 40
> > bytes of
> > > +the IPv6 header, plus 65535 bytes of maximum IPv6 payload including any
> > > +extension header) otherwise 1514 bytes.
> > > +When VIRTIO_NET_F_HASH_REPORT is not negotiated, the required receive
> > buffer
> > > +size is either 65601 or 1526 bytes.
> > > +When VIRTIO_NET_F_HASH_REPORT is negotiated, the required receive buffer
> > > +size is either 65609 or 1534 bytes.
> > >
> > > \drivernormative{\paragraph}{Setting Up Receive Buffers}{Device Types /
> > Network Device / Device Operation / Setting Up Receive Buffers}
> > >
> > > +If VIRTIO_NET_F_HASH_REPORT is not negotiated, the size of the field
> > > +\field{struct virtio_net_hdr} is 12 bytes.
> > > +
> > > +If VIRTIO_NET_F_HASH_REPORT is negotiated, the size of the field
> > > +\field{struct virtio_net_hdr} is 20 bytes.
> >
> > For the receive side, is these needed?
> >
> > Other is ok to me.
> >
> > Thanks
> >
> >
> At the moment the virtio_net header size is equal for RX and TX
> So, if the VIRTIO_NET_F_HASH_REPORT is negotiated the header size will be
> 20 bytes for both directions..
> In TX direction the extra space is the header is currently not used (if I'm
> not mistaken).
YES.
>
>
> >
> > > +
> > > \begin{itemize}
> > > \item If VIRTIO_NET_F_MRG_RXBUF is not negotiated:
> > > \begin{itemize}
> > > \item If VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
> > VIRTIO_NET_F_GUEST_UFO,
> > > VIRTIO_NET_F_GUEST_USO4 or VIRTIO_NET_F_GUEST_USO6 are negotiated,
> > the driver SHOULD populate
> > > - the receive queue(s) with buffers of at least 65562 bytes.
> > > + the receive queue(s) with buffers of at least 65589 bytes plus
> > the size
> > > + of the \field{struct virtio_net_hdr}.
> > > \item Otherwise, the driver SHOULD populate the receive queue(s)
> > > - with buffers of at least 1526 bytes.
> > > + with buffers of at least 1514 bytes plus the size of the
> > > + \field{struct virtio_net_hdr}.
> > > \end{itemize}
> > > \item If VIRTIO_NET_F_MRG_RXBUF is negotiated, each buffer MUST be at
> > > -least the size of the struct virtio_net_hdr.
> > > +least the size of the \field{struct virtio_net_hdr}.
> > > \end{itemize}
> > >
> > > \begin{note}
> > > --
> > > 2.34.1
> > >
> > >
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