Re: [virtio-comment] [PATCH] Introduction of Virtio Network device interrupt coalescing feature

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Thu, 12 May 2022 11:07:39 +0300, Alvaro Karsz <alvaro.karsz@solid-run.com> wrote:
> 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.
>

I would like to know what scenarios this function can be used in, what problems
can be solved or what benefits can be obtained?

Thanks.

>
> 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
>
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