Re: [PATCH] virtio-net: support reset queue

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 09, 2022 at 05:01:58PM +0800, Xuan Zhuo wrote:
> This patch defines some requirements for virtio-net to support reset
> queues.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>  conformance.tex |  2 ++
>  content.tex     | 19 +++++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/conformance.tex b/conformance.tex
> index 42f8537..52b4879 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -136,6 +136,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Packet Transmission}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Setting Up Receive Buffers}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Processing of Incoming Packets}
> +\item \ref{drivernormative:Device Types / Network Device / Device Operation / Reset Virtqueue}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Packet Receive Filtering}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Setting MAC Address Filtering}
>  \item \ref{drivernormative:Device Types / Network Device / Device Operation / Control Virtqueue / Gratuitous Packet Sending}
> @@ -396,6 +397,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Packet Transmission}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Setting Up Receive Buffers}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Processing of Incoming Packets}
> +\item \ref{devicenormative:Device Types / Network Device / Device Operation / Reset Virtqueue}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Packet Receive Filtering}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Setting MAC Address Filtering}
>  \item \ref{devicenormative:Device Types / Network Device / Device Operation / Control Virtqueue / Gratuitous Packet Sending}
> diff --git a/content.tex b/content.tex
> index c6f116c..ce8e37a 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -4000,6 +4000,25 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
>  #define VIRTIO_NET_HASH_REPORT_UDPv6_EX        9
>  \end{lstlisting}
>  
> +\subsubsection{Reset Virtqueue}\label{sec:Device Types / Network Device / Device Operation / Reset Virtqueue}
> +
> +The receive and transmission virtqueues can implement reset based on Virtqueue
> +Reset (See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> +
> +\drivernormative{\paragraph}{Gratuitous Packet Sending}{Device Types / Network Device / Device Operation / Reset Virtqueue}
> +
> +The driver MUST NOT reset the control virtqueue.

Why not though? I am guessing if it does and command is in
progress, it won't know if it completed. So it's safest to retry
then? Reset as a way to recover from a VQ error seems useful for CVQ,
I don't like disabling it like this.
Besides, it's probably too late to make this change for 1.2 ...

> +
> +\devicenormative{\paragraph}{Gratuitous Packet Sending}{Device Types / Network Device / Device Operation / Reset Virtqueue}
> +
> +After automatic receive steering or RSS receive steering has completed the
> +selection of the queue, if the destination receive queue is in reset state,
> +the device MUST re-select a different random queue. If all receive queues are in
> +reset state, the device can drop the packet.
> +
> +A virtio-net device MUST support the above requirements in order to support
> +VIRTIO_F_RING_RESET.
> +

This is more a quality of implementation issue, no? So I'd say SHOULD
here.

>  \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue}
>  
>  The driver uses the control virtqueue (if VIRTIO_NET_F_CTRL_VQ is
> -- 
> 2.31.0