[PATCH] Introduction of Virtio Network device interrupt coalescing feature

[Alvaro Karsz <alvaro.karsz@solid-run.com>]

Control a network device interrupt coalescing parameters using the control virtqueue.
A new control class was added: VIRTIO_NET_CTRL_INTR_COAL.

This class provides 2 commands:
- VIRTIO_NET_CTRL_INTR_COAL_USECS_SET:
  Ask the network device to change the rx-usecs and tx-usecs parameters.
  rx-usecs - Time to delay an RX interrupt after packet arrival in microseconds.
  tx-usecs - Time to delay a TX interrupt after a sending a packet in microseconds.

- VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET:
  Ask the network device to change the rx-max-frames and tx-max-frames parameters.
  rx-max-frames - Number of packets to delay an RX interrupt after packet arrival.
  tx-max-frames - Number of packets to delay a TX interrupt after sending a packet.


Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
---
 content.tex | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/content.tex b/content.tex
index 7508dd1..a70cb27 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_INTR_COAL(55)] Device supports interrupt 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_INTR_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 +4467,44 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
 (necessarily when not using the legacy interface) little-endian.


+\paragraph{Interrupt Coalescing}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Interrupt Coalescing}
+
+If the VIRTIO_NET_F_INTR_COAL feature is negotiated, the driver can
+send control commands for dynamically changing the coalescing parameters.
+
+\begin{lstlisting}
+struct virtio_net_ctrl_coal_usec {
+    le32 tx_usecs;
+    le32 rx_usecs;
+};
+
+struct virtio_net_ctrl_coal_frames {
+    le32 tx_frames_max;
+    le32 rx_frames_max;
+};
+
+#define VIRTIO_NET_CTRL_INTR_COAL 6
+ #define VIRTIO_NET_CTRL_INTR_COAL_USECS_SET  0
+ #define VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET 1
+\end{lstlisting}
+
+The class VIRTIO_NET_CTRL_INTR_COAL has 2 commands:
+\begin{itemize}
+\item VIRTIO_NET_CTRL_INTR_COAL_USECS_SET: set the rx-usecs (time to delay an RX interrupt after packet arrival in microseconds) and tx-usecs (time to delay a TX interrupt after a sending a packet in microseconds) parameters.
+\item VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET: set the rx-max-frames (number of packets to delay an RX interrupt after packet arrival) and tx-max-frames (number of packets to delay a TX interrupt after sending a packet) parameters.
+\end{itemize}
+
+\drivernormative{\subparagraph}{Interrupt Coalescing}{Device Types / Network Device / Device Operation / Control Virtqueue / Interrupt Coalescing}
+
+
+A driver MUST NOT send to the device VIRTIO_NET_CTRL_INTR_COAL commands if the VIRTIO_NET_F_INTR_COAL feature
+has not been negotiated.
+
+\devicenormative{\subparagraph}{Interrupt Coalescing}{Device Types / Network Device / Device Operation / Control Virtqueue / Interrupt Coalescing}
+
+A device SHOULD respond to the VIRTIO_NET_CTRL_INTR_COAL commands with VIRTIO_NET_ERR if was not able to change the parameters.
+
+
 \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device
 Types / Network Device / Legacy Interface: Framing Requirements}

--
2.32.0