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| -rw-r--r-- | content.tex | 104 |
1 files changed, 91 insertions, 13 deletions
diff --git a/content.tex b/content.tex index 8cfc36f..356a1d5 100644 --- a/content.tex +++ b/content.tex @@ -2285,12 +2285,18 @@ features. \subsection{Virtqueues}\label{sec:Device Types / Network Device / Virtqueues} \begin{description} -\item[0] receiveq -\item[1] transmitq -\item[2] controlq +\item[0] receiveq0 +\item[1] transmitq0 +\item[...] +\item[2N] receiveqN +\item[2N+1] transmitqN +\item[2N+2] controlq \end{description} - Virtqueue 2 only exists if VIRTIO_NET_F_CTRL_VQ set. + N=0 if VIRTIO_NET_F_MQ is not negotiated, otherwise N is derived + from max_virtqueue_pairs control field. + + controlq only exists if VIRTIO_NET_F_CTRL_VQ set. \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits} @@ -2333,6 +2339,10 @@ features. \item[VIRTIO_NET_F_GUEST_ANNOUNCE(21)] Driver can send gratuitous packets. + +\item[VIRTIO_NET_F_MQ(22)] Device supports multiqueue with automatic + receive steering. + \end{description} \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits} @@ -2346,7 +2356,7 @@ were required. \subsection{Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout} -Two configuration fields are currently defined. The mac address field +Three configuration fields are currently defined. The mac address field always exists (though is only valid if VIRTIO_NET_F_MAC is set), and the status field only exists if VIRTIO_NET_F_STATUS is set. Two read-only bits are currently defined for the status field: @@ -2355,10 +2365,20 @@ VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. \begin{lstlisting} #define VIRTIO_NET_S_LINK_UP 1 #define VIRTIO_NET_S_ANNOUNCE 2 +\end{lstlisting} +The following read-only field, max_virtqueue_pairs only exists if +VIRTIO_NET_F_MQ is set. This field specifies the maximum number +of each of transmit and receive virtqueues (receiveq0..receiveqN +and transmitq0..transmitqN respectively; + N=max_virtqueue_pairs - 1) that can be configured once VIRTIO_NET_F_MQ +is negotiated. Legal values for this field are 1 to 0x8000. + +\begin{lstlisting} struct virtio_net_config { u8 mac[6]; le16 status; + u16 max_virtqueue_pairs; }; \end{lstlisting} @@ -2371,7 +2391,9 @@ native endian of the guest rather than (necessarily) little-endian. \begin{enumerate} \item The initialization routine should identify the receive and - transmission virtqueues. + transmission virtqueues, up to N+1 of each kind. If + VIRTIO_NET_F_MQ feature bit is negotiated, + N=max_virtqueue_pairs-1, otherwise identify N=0. \item If the VIRTIO_NET_F_MAC feature bit is set, the configuration space “mac” entry indicates the “physical” address of the the @@ -2386,9 +2408,18 @@ native endian of the guest rather than (necessarily) little-endian. status can be read from the bottom bit of the “status” config field. Otherwise, the link should be assumed active. -\item The receive virtqueue should be filled with receive buffers. - This is described in detail below in “Setting Up Receive - Buffers”. +\item Only receiveq0, transmitq0 and controlq are used by default. + To use more queues driver must negotiate the VIRTIO_NET_F_MQ + feature; initialize up to max_virtqueue_pairs of each of + transmit and receive queues; + execute_VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET command specifying the + number of the transmit and receive queues that is going to be + used and wait until the device consumes the controlq buffer and + acks this command. + The receive virtqueue should be filled with receive buffers + before multiqueue is activated + (see \ref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode}~\nameref{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode}). + This is described in detail below in \nameref{sec:Device Types / Network Device / Device Operation / Setting Up Receive Buffers}. \item A driver can indicate that it will generate checksumless packets by negotating the VIRTIO_NET_F_CSUM feature. This @@ -2424,9 +2455,10 @@ if both guests are amenable. \subsection{Device Operation}\label{sec:Device Types / Network Device / Device Operation} -Packets are transmitted by placing them in the transmitq, and -buffers for incoming packets are placed in the receiveq. In each -case, the packet itself is preceeded by a header: +Packets are transmitted by placing them in the +transmitq0..transmitqN, and buffers for incoming packets are +placed in the receiveq0..receiveqN. In each case, the packet +itself is preceeded by a header: \begin{lstlisting} struct virtio_net_hdr { @@ -2550,6 +2582,9 @@ elements. If VIRTIO_NET_F_MRG_RXBUF is negotiated, each buffer must be at least the size of the struct virtio_net_hdr. +If VIRTIO_NET_F_MQ is negotiated, each of receiveq0...receiveqN +that will be used should be populated with receive buffers. + \paragraph{Packet Receive Interrupt}\label{sec:Device Types / Network Device / Device Operation / Setting Up Receive Buffers / Packet Receive Interrupt} When a packet is copied into a buffer in the receiveq, the @@ -2588,7 +2623,7 @@ Processing packet involves: \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue} -The driver uses the control virtqueue (if VIRTIO_NET_F_VTRL_VQ is +The driver uses the control virtqueue (if VIRTIO_NET_F_CTRL_VQ is negotiated) to send commands to manipulate various features of the device which would not easily map into the configuration space. @@ -2713,6 +2748,49 @@ Processing this notification involves: vq. \end{enumerate} +\paragraph{Automatic receive steering in multiqueue mode}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Automatic receive steering in multiqueue mode} + +If the driver negotiates the VIRTIO_NET_F_MQ feature bit (depends +on VIRTIO_NET_F_CTRL_VQ), it can transmit outgoing packets on one +of the multiple transmitq0..transmitqN and ask the device to +queue incoming packets into one the multiple receiveq0..receiveqN +depending on the packet flow. + +\begin{lstlisting} + struct virtio_net_ctrl_mq { + u16 virtqueue_pairs; + }; + + #define VIRTIO_NET_CTRL_MQ 4 + #define VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET 0 + #define VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN 1 + #define VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX 0x8000 +\end{lstlisting} + +Multiqueue is disabled by default. Driver enables multiqueue by +executing the VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET command, specifying +the number of the transmit and receive queues that will be used; +thus transmitq0..transmitqn and receiveq0..receiveqn where +n=virtqueue_pairs-1 will be used. All these virtqueues must have +been pre-configured in advance. The range of legal values for the +virtqueue_pairs field is between 1 and max_virtqueue_pairs. + +When multiqueue is enabled, device uses automatic receive steering +based on packet flow.Programming of the receive steering +classificator is implicit. Transmitting a packet of a specific +flow on transmitqX will cause incoming packets for this flow to +be steered to receiveqX. For uni-directional protocols, or where +no packets have been transmitted yet, device will steer a packet +to a random queue out of the specified receiveq0..receiveqn. + +Multiqueue is disabled by setting virtqueue_pairs = 1 (this is +the default). After the command is consumed by the device, the +device will not steer new packets on virtqueues +receveq1..receiveqN (i.e. other than receiveq0) nor read from +transmitq1..transmitqN (i.e. other than transmitq0); accordingly, +driver should not transmit new packets on virtqueues other than +transmitq0. + \paragraph{Offloads State Configuration}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Offloads State Configuration} If the VIRTIO_NET_F_CTRL_GUEST_OFFLOADS feature is negotiated, the driver can |