On Fri, Feb 17, 2023 at 10:42:21AM +0200, Alvaro Karsz wrote:
> Hi Heng,
>
> > +\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}
> > +
>
> Maybe we can use struct virtio_net_ctrl_coal inside struct
> virtio_net_ctrl_coal_vq instead of repeating max_usecs and
> max_packets?
> I'm not sure if it would be confusing, what do you think?
>
Hi Alvaro.
I guess you mean one of the following two forms:
#1
struct virtio_net_ctrl_coal {
le32 max_packets;
le32 max_usecs;
};
struct virtio_net_ctrl_coal_vq {
le16 vqn;
le16 reserved;
struct virtio_net_ctrl_coal coal;
} coal_vq;
#2
struct virtio_net_ctrl_coal {
le32 max_packets;
le32 max_usecs;
le16 vqn; // if _F_VQ_NOTF_COAL is negotiated
le16 reserved; // if _F_VQ_NOTF_COAL is negotiated
};
If it's #1, I think the format is a bit ugly, it's not semantic to use coal_vq
to send global commands when _F_VQ_NOTF_COAL is not negotiated, and the
presence of vqn and reserved is awkward.
If it's #2, I think this is a bit like the v1 version, using
virtio_net_ctrl_coal as a virtual queue to send commands does not seem to be
semantic, but it is indeed more unified in function.
I think we should hear from Michael and Parav.
> > +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.
> > +
>
> max_packets is the same with VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET and with
> VIRTIO_NET_CTRL_NOTF_COAL_[T/R]X_SET.
> ("Maximum number of packets to receive/send before a RX/TX notification").
> The fact that this is applied to all VQs or to a specific one is
> derived from the command.
> Same for max_usecs.
> Maybe we can join the coalescing parameters somehow instead of
> repeating the explanations?
>
> > +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.
>
> Both sentences seem similar to me.
Yes, this is an irrelevant modification, I will remove this modification.
>
> > +\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.
> >
>
> Maybe we can add here that the driver must ignore the values received
> from VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET, if the device responds with
> VIRTIO_NET_ERR?
Good idea.
Thanks.
>
> > \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.
> > +
> > +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.
>
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