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Subject: Re: [virtio-comment] [PATCH] virtio-net: Add equal-sized receive buffers feature
----- Original Message ----- > From: "Vitaly Mireyno" <vmireyno@marvell.com> > To: virtio-comment@lists.oasis-open.org > Cc: "Michael S. Tsirkin" <mst@redhat.com>, "Jason Wang" <jasowang@redhat.com> > Sent: Thursday, October 31, 2019 11:23:52 AM > Subject: [virtio-comment] [PATCH] virtio-net: Add equal-sized receive buffers > feature > Some devices benefit from working with receive buffers of a predefined > constant length. > Add a feature for drivers that allocate equal-sized receive buffers, and > devices that benefit from predefined receive buffers length. > Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> > --- > content.tex | 29 +++++++++++++++++++++++++++-- > 1 file changed, 27 insertions(+), 2 deletions(-) > diff --git a/content.tex b/content.tex > index b1ea9b9..c9e67c8 100644 > --- a/content.tex > +++ b/content.tex > @@ -2811,6 +2811,10 @@ \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_CONST_RXBUF_LEN(58)] Driver allocates all receive buffers > + of the same constant length. Device benefits from working with > + receive buffers of equal length. > + > \item[VIRTIO_NET_F_RSC_EXT(61)] Device can process duplicated ACKs > and report number of coalesced segments and duplicated ACKs > @@ -2854,8 +2858,8 @@ \subsubsection{Legacy Interface: Feature > bits}\label{sec:Device Types / Network > \subsection{Device configuration layout}\label{sec:Device Types / Network > Device / Device configuration layout} > \label{sec:Device Types / Block Device / Feature bits / Device configuration > layout} > -Three driver-read-only configuration fields are currently defined. The > \field{mac} address field > -always exists (though is only valid if VIRTIO_NET_F_MAC is set), and > +The driver-read-only \field{mac} address field always exists > +(though is only valid if VIRTIO_NET_F_MAC is set), and > \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two > read-only bits (for the driver) are currently defined for the status field: > VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. > @@ -2875,12 +2879,17 @@ \subsection{Device configuration > layout}\label{sec:Device Types / Network Device > VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU for the driver > to > use. > +The device-read-only field \field{rx_buf_len} only exists if > +VIRTIO_NET_F_CONST_RXBUF_LEN is negotiated. This field specifies the receive > +buffers length. > + > \begin{lstlisting} > struct virtio_net_config { > u8 mac[6]; > le16 status; > le16 max_virtqueue_pairs; > le16 mtu; > + le32 rx_buf_len; > }; > \end{lstlisting} Please see https://github.com/torvalds/linux/blob/master/include/uapi/linux/virtio_net.h Note that there are already 2 additional fields not covered by the spec at the moment. > @@ -2933,6 +2942,13 @@ \subsection{Device configuration > layout}\label{sec:Device Types / Network Device > A driver SHOULD negotiate the VIRTIO_NET_F_STANDBY feature if the device > offers it. > +A driver SHOULD accept the VIRTIO_NET_F_CONST_RXBUF_LEN feature if offered. > + > +If VIRTIO_NET_F_CONST_RXBUF_LEN feature has been negotiated, the driver MUST > +set \field{rx_buf_len}. > + > +A driver MUST NOT modify \field{rx_buf_len} once it has been set. > + > \subsubsection{Legacy Interface: Device configuration > layout}\label{sec:Device Types / Network Device / Device configuration > layout / Legacy Interface: Device configuration layout} > \label{sec:Device Types / Block Device / Feature bits / Device configuration > layout / Legacy Interface: Device configuration layout} > When using the legacy interface, transitional devices and drivers > @@ -3241,6 +3257,11 @@ \subsubsection{Setting Up Receive > Buffers}\label{sec:Device Types / Network Devi > If VIRTIO_NET_F_MQ is negotiated, each of receiveq1\ldots receiveqN > that will be used SHOULD be populated with receive buffers. > +If VIRTIO_NET_F_CONST_RXBUF_LEN feature has been negotiated, the driver > +MUST initialize all receive virtqueue descriptors \field{len} field with > +the value configured in \field{rx_buf_len} device configuration field, > +and allocate receive buffers accordingly. > + > \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types / > Network Device / Device Operation / Setting Up Receive Buffers} > The device MUST set \field{num_buffers} to the number of descriptors used to > @@ -3396,6 +3417,10 @@ \subsubsection{Processing of Incoming > Packets}\label{sec:Device Types / Network > checksum (in case of multiple encapsulated protocols, one level > of checksums is validated). > +If VIRTIO_NET_F_CONST_RXBUF_LEN has been negotiated, the device MAY > +use \field{rx_buf_len} as a buffer length (instead of reading it from > +virtqueue descriptor \field{len} field). > + > \drivernormative{\paragraph}{Processing of Incoming > Packets}{Device Types / Network Device / Device Operation / > Processing of Incoming Packets} > -- > This publicly archived list offers a means to provide input to the > OASIS Virtual I/O Device (VIRTIO) TC. > In order to verify user consent to the Feedback License terms and > to minimize spam in the list archive, subscription is required > before posting. > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > List help: virtio-comment-help@lists.oasis-open.org > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > Committee: https://www.oasis-open.org/committees/virtio/ > Join OASIS: https://www.oasis-open.org/join/
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