On Thu, Feb 16, 2023 at 10:43:01PM +0800, Heng Qi wrote:
> Currently coalescing parameters are grouped for all transmit and receive
> virtqueues. This patch supports setting or getting the parameters for a
> specified virtqueue, and a typical application of this function is netdim[1].
>
> When the traffic between virtqueues is unbalanced, for example, one virtqueue
> is busy and another virtqueue is idle, then it will be very useful to
> control coalescing parameters at the virtqueue granularity.
>
> [1] https://docs.kernel.org/networking/net_dim.html
>
> Signed-off-by: Heng Qi <[email protected]>
> Reviewed-by: Xuan Zhuo <[email protected]>
> ---
> v2->v3:
> 1. Add the netdim link. @Parav Pandit
> 2. VIRTIO_NET_F_VQ_NOTF_COAL no longer depends on VIRTIO_NET_F_NOTF_COAL.
> @Michael S. Tsirkin, @Alvaro Karsz
> 3. _VQ_GET is explained more. @Michael S. Tsirkin
> 4. Add more examples to avoid misunderstandings. @Michael S. Tsirkin
> 5. Clarify some statements. @Michael S. Tsirkin, @Parav Pandit, @Alvaro
> Karsz
> 6. Adjust the virtio_net_ctrl_coal_vq structure. @Michael S. Tsirkin
> 7. Fix some typos. @Michael S. Tsirkin
>
> v1->v2:
> 1. Rename VIRTIO_NET_F_PERQUEUE_NOTF_COAL to VIRTIO_NET_F_VQ_NOTF_COAL.
> @Michael S. Tsirkin
> 2. Use the \field{vqn} instead of the qid. @Michael S. Tsirkin
> 3. Unify tx and rx control structres into one structure
> virtio_net_ctrl_coal_vq. @Michael S. Tsirkin
> 4. Add a new control command VIRTIO_NET_CTRL_NOTF_COAL_VQ. @Michael S.
> Tsirkin, @Parav Pandit, @Alvaro Karsz
> 5. The special value 0xFFF is removed because VIRTIO_NET_CTRL_NOTF_COAL
> can be used. @Alvaro Karsz
> 6. Clarify some special scenarios. @Michael S. Tsirkin, @Parav Pandit,
> @Alvaro Karsz
>
> content.tex | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 126 insertions(+), 4 deletions(-)
>
> diff --git a/content.tex b/content.tex
> index e863709..7f99503 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -3084,6 +3084,9 @@ \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_VQ_NOTF_COAL(52)] Device supports the virtqueue
> + notifications coalescing.
> +
> \item[VIRTIO_NET_F_NOTF_COAL(53)] Device supports notifications coalescing.
>
> \item[VIRTIO_NET_F_GUEST_USO4 (54)] Driver can receive USOv4 packets.
> @@ -3140,6 +3143,7 @@ \subsubsection{Feature bit
> requirements}\label{sec:Device Types / Network Device
> \item[VIRTIO_NET_F_NOTF_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.
> +\item[VIRTIO_NET_F_VQ_NOTF_COAL] Requires VIRTIO_NET_F_CTRL_VQ.
> \end{description}
>
> \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types /
> Network Device / Feature bits / Legacy Interface: Feature bits}
> @@ -4501,8 +4505,11 @@ \subsubsection{Control Virtqueue}\label{sec:Device
> Types / Network Device / Devi
> };
>
> #define VIRTIO_NET_CTRL_NOTF_COAL 6
> - #define VIRTIO_NET_CTRL_NOTF_COAL_TX_SET 0
> + #define VIRTIO_NET_CTRL_NOTF_COAL_TX_SET 0
> #define VIRTIO_NET_CTRL_NOTF_COAL_RX_SET 1
> + #define VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET 2
> + #define VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET 3
> +
> \end{lstlisting}
>
> Coalescing parameters:
> @@ -4514,12 +4521,67 @@ \subsubsection{Control Virtqueue}\label{sec:Device
> Types / Network Device / Devi
> \end{itemize}
>
>
> -The class VIRTIO_NET_CTRL_NOTF_COAL has 2 commands:
> +The class VIRTIO_NET_CTRL_NOTF_COAL has 4 commands:
> \begin{enumerate}
> \item VIRTIO_NET_CTRL_NOTF_COAL_TX_SET: set the \field{tx_usecs} and
> \field{tx_max_packets} parameters.
> \item VIRTIO_NET_CTRL_NOTF_COAL_RX_SET: set the \field{rx_usecs} and
> \field{rx_max_packets} parameters.
> +\item VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET: set the \field{max_packets} and
> \field{max_usecs} parameters for a enabled
> + transmit/receive virtqueue whose
> number is \field{vqn}.
> +\item VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET: the device gets the
> \field{max_packets} and \field{max_usecs} parameters of
> + a enabled transmit/receive virtqueue
> whose number is \field{vqn}, and then
> + responds them to the driver.
> \end{enumerate}
>
> +If the VIRTIO_NET_F_VQ_NOTF_COAL feature is negotiated:
> +1. a driver can send a VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command to set the
> coalescing
> + parameters of a enabled transmit/receive virtqueue.
> +2. a driver can send a VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET command to a device,
> and the device
> + responds to the driver with the coalescing parameters of a enabled
> transmit/receive virtqueue.
> +
> +\begin{lstlisting}
> +struct virtio_net_ctrl_coal_vq {
> + le16 vqn;
> + le16 reserved;
> + le32 max_packets;
> + le32 max_usecs;
> +};
> +\end{lstlisting}
> +
> +Virtqueue coalescing parameters:
> +\begin{itemize}
> +\item \field{vqn}: The virtqueue number of the enabled transmit or receive
> virtqueue, excluding the control virtqueue.
> +\item \field{max_packets}: The maximum number of packets sent/received by
> the specified virtqueue before a TX/RX notification.
> +\item \field{max_usecs}: The maximum number of TX/RX usecs that the
> specified virtqueue delays a TX/RX notification.
> +\end{itemize}
> +
> +\field{reserved} is reserved and it is ignored by the device.
> +
> +THe value of \field{vqn} satisfies $ 0 \leq vqn < max_virtqueue_pairs \ast 2
> $.
> +The conversion between \field{vqn} and transmitq/receiveq index:
> +\begin{itemize}
> +$ \lfloor vqn / 2 \rfloor $ is the index of the corresponding receiveq.
> +$ \lfloor (vqn / 2) + 1 \rfloor $ is the index of the corresponding tranmitq.
> +\end{itemize}
> +
> +The VIRTIO_NET_CTRL_NOTF_COAL_RX_SET command is the same as the
> VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET
> +command repeated for each virtqueue of receiveq1\ldots receiveqN.
> +
> +The VIRTIO_NET_CTRL_NOTF_COAL_TX_SET command is the same as the
> VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET
> +command repeated for each virtqueue of transmitq1\ldots transmitqN.
> +
> +If coalescing parameters are being set, the device applies the last
> coalescing parameters received for a
> +virtqueue, regardless of the command used to deliver the parameters. For
> example:
> +# Command sequence 1:
> +1. VIRTIO_NET_CTRL_NOTF_COAL_RX_SET command with $ \field{max_packets} = 15
> $ and $ \field{max_usecs} = 10 $
> +2. VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command with $ \field{vqn} = 0 $, $
> \field{max_packets} = 12 $ and $ \field{max_usecs} = 8 $
> +After #2 command is applied by the device, the coalescing parameters of
> receiveq1 are $ \field{max_packets} = 12 $ and $ \field{max_usecs} = 8 $,
> +and the coalescing parameters of receiveq2\ldots receiveqN are $
> \field{max_packets} = 15 $ and $ \field{max_usecs} = 10 $.
> +
> +# Command sequence 2:
> +1. VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command with $ \field{vqn} = 0 $, $
> \field{max_packets} = 12 $ and $ \field{max_usecs} = 8 $
> +2. VIRTIO_NET_CTRL_NOTF_COAL_RX_SET command with $ \field{max_packets} = 15
> $ and $ \field{max_usecs} = 10 $
> +After #2 command is applied by the device, the coalescing parameters of
> receiveq1\ldots receiveqN are $ \field{max_packets} = 15 $ and $
> \field{max_usecs} = 10 $.
> +
> \subparagraph{RX Notifications}\label{sec:Device Types / Network Device /
> Device Operation / Control Virtqueue / Notifications Coalescing / RX
> Notifications}
>
> If, for example:
> @@ -4532,9 +4594,33 @@ \subsubsection{Control Virtqueue}\label{sec:Device
> Types / Network Device / Devi
>
> \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.
> +\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}
> +
> +Example of setting coalescing parameters for a receive virtqueue:
> +\begin{itemize}
> +\item \field{max_packets} = 15
> +\item \field{max_usecs} = 10
> +\item \field{vqn} = 0
> +\end{itemize}
> +
> +The device will operate as follows:
> +\begin{itemize}
> +\item The device applies the coalescing parameters to receiveq1 because its
> virtqueue number is 0.
> +\item The device will count received packets on receiveq1 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}
> +
> +Example of getting coalescing parameters from a receive virtqueue:
> +\begin{itemize}
> +\item \field{vqn} = 0.
> \end{itemize}
>
> +The device gets the values of the \field{max_packets} and \field{max_usecs}
> parameters from the receiveq1 whose virtqueue number is 0,
> +and then responds them to the driver.
> +
> \subparagraph{TX Notifications}\label{sec:Device Types / Network Device /
> Device Operation / Control Virtqueue / Notifications Coalescing / TX
> Notifications}
>
> If, for example:
> @@ -4550,14 +4636,50 @@ \subsubsection{Control Virtqueue}\label{sec:Device
> Types / Network Device / Devi
> \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}
>
> +Example of setting coalescing parameters for a transmit virtqueue:
> +\begin{itemize}
> +\item \field{max_packets} = 15
> +\item \field{max_usecs} = 10
> +\item \field{vqn} = 1
> +\end{itemize}
> +
> +The device will operate as follows:
> +
> +\begin{itemize}
> +\item The device applies the coalescing parameters to transmitq1 because its
> virtqueue number is 1.
> +\item The device will count sent packets on transmitq1 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}
> +
> +Example of getting coalescing parameters from a transmit virtqueue:
> +\begin{itemize}
> +\item \field{vqn} = 1.
> +\end{itemize}
> +
> +The device gets the values of the \field{max_packets} and \field{max_usecs}
> parameters from the transmitq1 whose virtqueue number is 1,
> +and then responds them to 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.
> +If neither the VIRTIO_NET_F_NOTF_COAL nor the VIRTIO_NET_F_VQ_NOTF_COAL
> feature
> +has not been negotiated, the driver MUST NOT issue VIRTIO_NET_CTRL_NOTF_COAL
> commands.
> +
> +If the VIRTIO_NET_F_VQ_NOTF_COAL feature is negotiated, the driver MUST set
> \field{vqn}
> +to a legal value, that is, \field{vqn} points to an enabled transmit/receive
> virtqueue.
> +
> +A driver MAY NOT get exactly the same value as the coalescing parameter it
> was set to, for example it MAY get a value that is a power of 2.
>
> \devicenormative{\subparagraph}{Notifications Coalescing}{Device Types /
> Network Device / Device Operation / Control Virtqueue / Notifications
> Coalescing}
>
> 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.
>
> +When a device receives a virtqueue command to set/get coalescing parameters
> for a virtqueue with number \field{vqn},
> +if the virtqueue is not enabled, the device SHOULD respond to the command
> with VIRTIO_NET_ERR.
What if vq is disabled? do parameters reset?
What about VIRTIO_NET_CTRL_NOTF_COAL?
what if it is envoked while some vq is disabled then vq is enabled?
do parameters for this vq stay 0?
> +
> +A device MAY NOT set the coalescing parameter to the exact same value as the
> one passed in by a driver. For example,
> +the value of \field{max_packets} set by the driver is 15, but the device MAY
> store a value that is a power of 2, that is, 16.
> +
> 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.
>
> Upon reset, a device MUST initialize all coalescing parameters to 0.
> --
> 2.19.1.6.gb485710b
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