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Subject: [PATCH v6] Introduction of Virtio Network device notifications coalescing feature.
Control a network device notifications coalescing parameters using the control virtqueue. A new control class was added: VIRTIO_NET_CTRL_NOTF_COAL. This class provides 2 commands: - VIRTIO_NET_CTRL_NOTF_COAL_TX_SET: Ask the network device to change the tx_usecs and tx_max_packets parameters. - tx_usecs: How many usecs to delay an TX notification after a packet is sent. - tx_max_packets: Maximum number of packets to send before an TX notification. - VIRTIO_NET_CTRL_NOTF_COAL_RX_SET: Ask the network device to change the rx_usecs and rx_max_packets parameters. - rx_usecs: How many usecs to delay an RX notification after a packet arrives. - rx_max_packets: Maximum number of packets to receive before an RX notification. -- v2: - Usage of notification terminology. - Add a few lines on what device should do when driver asked to suppress notifications. v3: - Remove whitespaces. - Explain with examples how the device should act. v4: - Example of a scenarion when VIRTIO_F_EVENT_IDX is negotiated. - Usage of separate commands for RX coalescing and TX coalescing. v5: - Usage of subparagraphs. - Add driver requirements and device requirements references in conformance.tex. v6: - LaTex formatting fixes. - Clarify the meaning of every coalescing parameter. - Usage of packets terminology instead of used buffers. -- Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com> --- conformance.tex | 2 + content.tex | 103 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 105 insertions(+) diff --git a/conformance.tex b/conformance.tex index 663e7c3..c9ccc89 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 / Notifications Coalescing} \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 / Notifications Coalescing} \end{itemize} \conformance{\subsection}{Block Device Conformance}\label{sec:Conformance / Device Conformance / Block Device Conformance} diff --git a/content.tex b/content.tex index 7508dd1..f5447a7 100644 --- a/content.tex +++ b/content.tex @@ -3084,6 +3084,8 @@ \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_NOTF_COAL(55)] Device supports notifications coalescing. + \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. @@ -3129,6 +3131,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device \item[VIRTIO_NET_F_GUEST_ANNOUNCE] Requires VIRTIO_NET_F_CTRL_VQ. \item[VIRTIO_NET_F_MQ] Requires VIRTIO_NET_F_CTRL_VQ. \item[VIRTIO_NET_F_CTRL_MAC_ADDR] Requires VIRTIO_NET_F_CTRL_VQ. +\item[VIRTIO_NET_F_NOTF_COAL] 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. \end{description} @@ -4464,6 +4467,106 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi (necessarily when not using the legacy interface) little-endian. +\paragraph{Notifications Coalescing}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing} + +If the VIRTIO_NET_F_NOTF_COAL feature is negotiated, the driver can +send control commands for dynamically changing the coalescing parameters. + +\begin{lstlisting} +struct virtio_net_ctrl_coal_rx { + le32 rx_max_packets; + le32 rx_usecs; +}; + +struct virtio_net_ctrl_coal_tx { + le32 tx_max_packets; + le32 tx_usecs; +}; + +#define VIRTIO_NET_CTRL_NOTF_COAL 6 + #define VIRTIO_NET_CTRL_NOTF_COAL_TX_SET 0 + #define VIRTIO_NET_CTRL_NOTF_COAL_RX_SET 1 +\end{lstlisting} + +Coalescing parameters: +\begin{itemize} +\item \field{rx_usecs}: How many usecs to delay an RX notification after a packet arrives. +\item \field{tx_usecs}: How many usecs to delay an TX notification after a packet is sent. +\item \field{rx_max_packets}: Maximum number of packets to receive before an RX notification. +\item \field{tx_max_packets}: Maximum number of packets to send before an TX notification. +\end{itemize} + + +The class VIRTIO_NET_CTRL_NOTF_COAL has 2 commands: +\begin{enumerate} +\item VIRTIO_NET_CTRL_NOTF_COAL_TX_SET: set the \field{tx_usecs} and \field{tx_max_packets} parameters. +\item VIRTIO_NET_CTRL_NOTF_COAL_RX_SET: set the \field{rx_usecs} and \field{rx_max_packets} parameters. +\end{enumerate} + +\subparagraph{RX Notifications}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing / RX Notifications} + +If, for example: +\begin{itemize} +\item \field{rx_usecs} = 10. +\item \field{rx_max_packets} = 15. +\end{itemize} + +The device will operate as follows: + +\begin{itemize} +\item The device will count received packets until it accumulates 15, or until 10 usecs elapsed since the first one arrived. +\item If the nofitications are not suppressed by the driver, the device will send a notification, otherwise, the device will not send a notification. +\end{itemize} + +Note: If VIRTIO_NET_F_MRG_RXBUF feature is negotiated, all merged buffers together count as one packet. + +\subparagraph{TX Notifications}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing / TX Notifications} + +If, for example: +\begin{itemize} +\item \field{tx_usecs} = 10. +\item \field{tx_max_packets} = 15. +\end{itemize} + +The device will operate as follows: + +\begin{itemize} +\item The device will count sent packets until it accumulates 15, or until 10 usecs elapsed since the first one was sent. +\item If the nofitications are not suppressed by the driver, the device will send a notification, otherwise, the device will not send a notification. +\end{itemize} + +Note: A chain of buffers, chained by the driver using the \field{next} flag, count as one packet. + +\subparagraph{Coalescing and Notifications Suppression}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing / Coalescing and Notifications Suppression} + +If the driver sets the VIRTQ_AVAIL_F_NO_INTERRUPT flag, the device should not send notifications to the driver. +In this case, the device will increase the coalescing counters until the flag is cleared, and only then the device will send a notification and clear the coalescing counters. + +If the VIRTIO_F_EVENT_IDX feature is negotiated, and \field{used_event} field is set, the device will send a notification only after \field{used_event} index is reached, even if the coalescing counters expired before. + +For example: +\begin{itemize} +\item \field{rx_usecs} = 10. +\item \field{rx_max_packets} = 7. +\item \field{used_event} = 5. +\item Current virtqueue location is 0. +\end{itemize} + +If the timer elapses before the \#5 packet arrives, the device will send a notification only after the \#5 packet arrives. +If the \#5 packet arrives before the timer elapses, the device will send a notification after the \#7 packet arrives, or after the timer elapses, whichever occurs first. + +\drivernormative{\subparagraph}{Notifications Coalescing}{Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing} + +If the VIRTIO_NET_F_NOTF_COAL feature has not been negotiated, the driver MUST NOT issue VIRTIO_NET_CTRL_NOTF_COAL commands. + +\devicenormative{\subparagraph}{Notifications Coalescing}{Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing} + +A device SHOULD respond to the VIRTIO_NET_CTRL_NOTF_COAL commands with VIRTIO_NET_ERR if it was not able to change the parameters. + +A device SHOULD NOT send notifications to the driver, if the notifications are suppressed. + +Upon reset, a device MUST initialize all coalescing parameters to 0. + \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device Types / Network Device / Legacy Interface: Framing Requirements} -- 2.32.0
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