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.
>
>
> > +
> > +\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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