RE: [PATCH v5] virtio-net: Fix and update VIRTIO_NET_F_NOTF_COAL feature

[Parav Pandit <parav@nvidia.com>]

> From: Alvaro Karsz <alvaro.karsz@solid-run.com>
> Sent: Thursday, February 16, 2023 9:56 AM

[..]
> +When the device has \field{max_usecs} = 0 or \field{max_packets} = 0, the
> notification conditions are met after every packet received/sent.
> +

> +\subparagraph{RX Example}\label{sec:Device Types / Network Device /
> +Device Operation / Control Virtqueue / Notifications Coalescing / RX
> +Example}
> 
>  If, for example:
>  \begin{itemize}
> -\item \field{rx_usecs} = 10.
> -\item \field{rx_max_packets} = 15.
> +\item \field{max_usecs} = 10.
> +\item \field{max_packets} = 15.
>  \end{itemize}
> -
> -The device will operate as follows:
> -
> +then a device with a single receive virtqueue 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 was received.
>  \item If the notifications are not suppressed by the driver, the device will send
> an used buffer notification, otherwise, the device will not send an used buffer
> notification as long as the notifications are suppressed.
>  \end{itemize}
> 
> -\subparagraph{TX Notifications}\label{sec:Device Types / Network Device /
> Device Operation / Control Virtqueue / Notifications Coalescing / TX
> Notifications}
> +\subparagraph{TX Example}\label{sec:Device Types / Network Device /
> +Device Operation / Control Virtqueue / Notifications Coalescing / TX
> +Example}
> 
>  If, for example:
>  \begin{itemize}
> -\item \field{tx_usecs} = 10.
> -\item \field{tx_max_packets} = 15.
> +\item \field{max_usecs} = 10.
> +\item \field{max_packets} = 15.
>  \end{itemize}
> -
> -The device will operate as follows:
> -
> +then a device with a single transmit virtqueue 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 notifications are not suppressed by the driver, the device will send
> an used buffer notification, otherwise, the device will not send an used buffer
> notification as long as the notifications are suppressed.
>  \end{itemize}
> 
> +\subparagraph{Notifications When Coalescing Parameters
> +Change}\label{sec:Device Types / Network Device / Device Operation /
> +Control Virtqueue / Notifications Coalescing / Notifications When
> +Coalescing Parameters Change}
> +
> +When the coalescing parameters of a device change, the device needs to
> check if the new notification conditions are met and send a used buffer
> notification if so.
> +
> +For example, \field{max_packets} = 15 for a device with a single
> +transmit virtqueue: if the device sends 10 packets and afterwards
> +receives a VIRTIO_NET_CTRL_NOTF_COAL_TX_SET command with
> \field{max_packets} = 8, then the notification condition is immediately
> considered to be met; the device needs to immediately send a used buffer
> notification, if the notifications are not suppressed by the driver.
> +
>  \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.
> @@ -1583,7 +1596,7 @@ \subsubsection{Control Virtqueue}\label{sec:Device
> Types / Network Device / Devi
> 
>  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 used buffer notifications to the driver, if the
> notifications are suppressed as explained in \ref{sec:Basic Facilities of a Virtio
> Device / Virtqueues / Used Buffer Notification Suppression}, even if the
> coalescing counters expired.
> +A device SHOULD NOT send used buffer notifications to the driver if the
> notifications are suppressed, even if the notification conditions are met.
> 
>  Upon reset, a device MUST initialize all coalescing parameters to 0.
> 
> --
> 2.34.1

Reviewed-by: Parav Pandit <parav@nvidia.com>