On Thu, May 26, 2022 at 2:31 PM Xuan Zhuo <[email protected]> wrote:
>
> On Mon, 9 May 2022 16:41:11 +0800, Jason Wang <[email protected]> wrote:
> >
> > 在 2022/5/7 15:15, Xuan Zhuo 写道:
> > > The purpose of this feature is to split the header and the payload of
> > > the packet.
> > >
> > > | receive buffer |
> > > | 0th descriptor | 1th descriptor |
> > > | virtnet hdr | mac | ip hdr | tcp hdr|<-- hold -->| payload |
> > >
> > > We can use a buffer plus a separate page when allocating the receive
> > > buffer. In this way, we can ensure that all payloads can be
> > > independently in a page, which is very beneficial for the zerocopy
> > > implemented by the upper layer.
> > >
> > > Signed-off-by: Xuan Zhuo <[email protected]>
> > > ---
> > > conformance.tex | 2 ++
> > > content.tex | 72 +++++++++++++++++++++++++++++++++++++++++++++++++
> > > 2 files changed, 74 insertions(+)
> > >
> > > diff --git a/conformance.tex b/conformance.tex
> > > index 663e7c3..6f561fb 100644
> > > --- a/conformance.tex
> > > +++ b/conformance.tex
> > > @@ -149,6 +149,7 @@ \section{Conformance Targets}\label{sec:Conformance /
> > > Conformance Targets}
> > > \item \ref{drivernormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Automatic receive steering in multiqueue
> > > mode}
> > > \item \ref{drivernormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Offloads State Configuration / Setting
> > > Offloads State}
> > > \item \ref{drivernormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Receive-side scaling (RSS) }
> > > +\item \ref{drivernormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Split Header}
> > > \end{itemize}
> > >
> > > \conformance{\subsection}{Block Driver
> > > Conformance}\label{sec:Conformance / Driver Conformance / Block Driver
> > > Conformance}
> > > @@ -411,6 +412,7 @@ \section{Conformance Targets}\label{sec:Conformance /
> > > Conformance Targets}
> > > \item \ref{devicenormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Gratuitous Packet Sending}
> > > \item \ref{devicenormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Automatic receive steering in multiqueue
> > > mode}
> > > \item \ref{devicenormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Receive-side scaling (RSS) / RSS
> > > processing}
> > > +\item \ref{devicenormative:Device Types / Network Device / Device
> > > Operation / Control Virtqueue / Split Header}
> > > \end{itemize}
> > >
> > > \conformance{\subsection}{Block Device
> > > Conformance}\label{sec:Conformance / Device Conformance / Block Device
> > > Conformance}
> > > diff --git a/content.tex b/content.tex
> > > index 060bdab..3340402 100644
> > > --- a/content.tex
> > > +++ b/content.tex
> > > @@ -3092,6 +3092,9 @@ \subsection{Feature bits}\label{sec:Device Types /
> > > Network Device / Feature bits
> > > \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control
> > > channel.
> > >
> > > +\item[VIRTIO_NET_F_SPLIT_HEADER (55)] Device supports to split the
> > > header and
> > > + the payload.
> > > +
> > > \item[VIRTIO_NET_F_HOST_USO (56)] Device can receive USO packets.
> > > Unlike UFO
> > > (fragmenting the packet) the USO splits large UDP packet
> > > to several segments when each of these smaller packets has UDP header.
> > > @@ -3139,6 +3142,7 @@ \subsubsection{Feature bit
> > > requirements}\label{sec:Device Types / Network Device
> > > \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ.
> > > \item[VIRTIO_NET_F_RSC_EXT] Requires VIRTIO_NET_F_HOST_TSO4 or
> > > VIRTIO_NET_F_HOST_TSO6.
> > > \item[VIRTIO_NET_F_RSS] Requires VIRTIO_NET_F_CTRL_VQ.
> > > +\item[VIRTIO_NET_F_SPLIT_HEADER] Requires VIRTIO_NET_F_CTRL_VQ.
> > > \end{description}
> > >
> > > \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types /
> > > Network Device / Feature bits / Legacy Interface: Feature bits}
> > > @@ -3370,6 +3374,7 @@ \subsection{Device Operation}\label{sec:Device
> > > Types / Network Device / Device O
> > > #define VIRTIO_NET_HDR_F_NEEDS_CSUM 1
> > > #define VIRTIO_NET_HDR_F_DATA_VALID 2
> > > #define VIRTIO_NET_HDR_F_RSC_INFO 4
> > > +#define VIRTIO_NET_HDR_F_SPLIT_HEADER 8
> > > u8 flags;
> > > #define VIRTIO_NET_HDR_GSO_NONE 0
> > > #define VIRTIO_NET_HDR_GSO_TCPV4 1
> > > @@ -4471,6 +4476,73 @@ \subsubsection{Control Virtqueue}\label{sec:Device
> > > Types / Network Device / Devi
> > > according to the native endian of the guest rather than
> > > (necessarily when not using the legacy interface) little-endian.
> > >
> > > +\paragraph{Split Header}\label{sec:Device Types / Network Device /
> > > Device Operation / Control Virtqueue / Split Header}
> > > +
> > > +If the VIRTIO_NET_F_SPLIT_HEADER feature is negotiated,
> > > +the device supports to split the header and the payload.
> > > +The header and payload will be separated into different buffers.
> >
> >
> > I think you meant "descriptors" instead of "buffers".
>
> Will fix.
>
> >
> >
> > > +
> > > +\subparagraph{Split Header}\label{sec:Device Types / Network Device /
> > > Device Operation / Control Virtqueue / Split Header / Setting Split
> > > Header}
> > > +
> > > +To configure the split header, the following layout structure and
> > > definitions
> > > +are used:
> > > +
> > > +\begin{lstlisting}
> > > +struct virtio_net_split_header_config {
> > > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_TCPv4 1
> >
> >
> > I think it's better to capitalize: TCPV4 or TCP4.
>
> OK.
>
> >
> >
> > > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_TCPv6 2
> > > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_UDPv4 4
> > > +#define VIRTIO_NET_SPLIT_HEADER_TYPE_UDPv6 8
> > > + le64 type;
> > > +};
> > > +
> > > +#define VIRTIO_NET_CTRL_SPLIT_HEADER 6
> > > + #define VIRTIO_NET_CTRL_SPLIT_HEADER_SET 0
> > > +\end{lstlisting}
> > > +
> > > +The class VIRTIO_NET_CTRL_SPLIT_HEADER has one command:
> > > +VIRTIO_NET_CTRL_SPLIT_HEADER_SET applies the new split header
> > > configuration.
> > > +
> > > +\field{type} passed as command data is a bitmask, bits set define
> > > +packet types to split header, bits cleared - split header to be disabled.
> >
> >
> > (Not a native speaker, try my best to help)
> >
> > This sentence might need some tweaks:
> >
> > The driver can enable or disable the split by setting or clearing
> > corresponding bits in \field{type}.
>
> Thanks.
>
> >
> >
> > > +
> > > +The header contains the struct virtio_net_hdr and the header of the
> > > package.
> > > +Such as \field{VIRTIO_NET_SPLIT_HEADER_TYPE_TCPv4} specified header
> > > contains
> > > +virtio_net_hdr, MAC header, IPv4 header (including IPv4 options), TCP
> > > header
> > > +(include TCP options). The back part is the payload.
> >
> >
> > I think it's better to either explain each type one by one instead of
> > only describing the TCPv4. Or we can simply say the head contains all
> > headers before level 4 payload?
>
> OK. Thanks.
>
>
> >
> >
> > > +
> > > +\devicenormative{\subparagraph}{Setting Split Header}{Device Types /
> > > Network Device / Device Operation / Control Virtqueue / Split Header}
> > > +
> > > +Split header MUST be disabled after device initialization.
> >
> >
> > I think you actually mean "upon device reset"?
>
> Yes.
>
>
> >
> >
> > > +
> > > +A device MUST NOT perform split header in the following cases:
> > > +\begin{itemize}
> > > + \item device does not recognize protocol of the packet.
> > > + \item \field{type} does not include the protocol of the packet.
> > > + \item the packet is a IP fragmentation.
> >
> >
> > What's the reason for this limit?
>
> Rethinking this problem, some implementation difficulties that I originally
> thought can be solved. So I think this limitation can be removed.
>
> >
> >
> > > + \item the receive buffer consists of only one descriptor.
> >
> >
> > descriptor actually.
>
> Will fix.
>
> >
> >
> > > + \item the header exceeds the size of the 0th descriptor.
> >
> >
> > It looks to me the spec count from the first.
>
> Will fix.
>
> >
> >
> > > + \item If VIRTIO_NET_F_MRG_RXBUF is not negotiated and the size of the
> > > + payload is greater than the total size of the 1th\ldots Nth
> > > descriptor.
> >
> >
> > Maybe something like the following is better:
> >
> > The size of the payload exceeds the length of the descriptor or buffer
> > chain starting from the 2nd descriptor.
>
> OK.
>
> >
> >
> > > +\end{itemize}
> > > +
> > > +If the split header completed,
> >
> >
> > If the header is split by the device?
>
> Yes.
>
> >
> >
> > > then the \field{flags} of virtnet hdr MUST
> >
> >
> > We can drop "then" here and it's better to use structure virtio_net_hdr
>
> Will fix.
>
> >
> >
> > > +contains VIRTIO_NET_HDR_F_SPLIT_HEADER. The header MUST is on the buffer
> > > of the
> > > +0th descriptor,
> >
> >
> > first and second should be used here.
>
> OK
>
> >
> >
> > > and the payload MUST starts from the buffer of the 1th descriptor.
> > > +The device MUST set \field{hdr_len} of virtnet hdr.
> >
> >
> > To what value?
>
> I'll make it clear in the next version.
>
> >
> >
> > > +
> > > +If VIRTIO_NET_F_MRG_RXBUF is negotiated and the device is to use multiple
> > > +receive buffers, each subsequent receive buffer MUST skip the 0th
> > > descriptor.
> >
> >
> > I don't see why we need this.
>
> If used to implement zerocopy, the second desc points to a page-aligned
> buffer.
> The first desc points to a small buffer for saving the header. The first
> buffer
> and subsequent buffers are generally discontinuous. So giving up the first
> buffer and directly guaranteeing the data to the page-aligned buffer can
> achieve
> better performance. And the driver can reuse the first buffer.
I see, it might be better if we can explain this here.
Thanks
>
> >
> >
> > > +
> > > +\drivernormative{\subparagraph}{Setting Split Header}{Device Types /
> > > Network Device / Device Operation / Control Virtqueue / Split Header}
> > > +
> > > +If VIRTIO_NET_HDR_F_SPLIT_HEADER bit in \field{flags} is set, the driver
> > > MUST
> > > +believe \field{hdr_len}, the length of the header in the 0th descriptor
> > > is equal
> > > +to the length of struct virtio_net_hdr plus \field{hdr_len}.
> >
> >
> > See above we can reuse the device normative an drop the second part
> > starting from " the length of the header ..."
>
> OK
>
> >
> >
> > > +
> > > +If the split header function is enable, the buffers submitted by the
> > > driver
> > > +SHOULD at least be composed of two descriptors.
> >
> >
> > Do we need to mention it's only used for RX? (I think we don't need this
> > for TX).
>
> Yes.
>
> >
> >
> > > The buffer specified by the 0th
> > > +descriptor SHOULD be able to accommodate the header.
> >
> >
> > We probably need to clarify that the header here means both the virtio
> > net header and the protocol header.
>
> Will fix.
>
> Thanks.
>
> >
> > Thanks
> >
> >
> > >
> > > \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
> > > Types / Network Device / Legacy Interface: Framing Requirements}
> >
> >
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> >
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