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Subject: Re: [virtio-comment] [PATCH v4] virtio-net: support the virtqueue coalescing moderation
On Sunday, 2023-02-19 at 22:45:07 +08, 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 <hengqi@linux.alibaba.com> > Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> > --- > This patch is on top of Alvaro's latest v7 patch: https://lists.oasis-open.org/archives/virtio-dev/202302/msg00431.html . > > v3->v4: > 1. Include virtio_net_ctrl_coal in the virtio_net_ctrl_coal_vq structure. @Alvaro Karsz > 2. Add consideration of vq reset. @Michael S. Tsirkin, @Parav Pandit, @Alvaro Karsz > 3. Avoid too many examples by giving a comprehensive example. @Michael S. Tsirkin > 4. Fix typos and streamline clarifications. @Michael S. Tsirkin, @Parav Pandit, @Alvaro Karsz > > 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 > > device-types/net/description.tex | 64 ++++++++++++++++++++++++++++++-- > 1 file changed, 60 insertions(+), 4 deletions(-) > > diff --git a/device-types/net/description.tex b/device-types/net/description.tex > index e71e33b..fa8bd26 100644 > --- a/device-types/net/description.tex > +++ b/device-types/net/description.tex > @@ -83,6 +83,8 @@ \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_VQ_NOTF_COAL(52)] Device supports virtqueue notification coalescing. > + > \item[VIRTIO_NET_F_NOTF_COAL(53)] Device supports notifications coalescing. > > \item[VIRTIO_NET_F_GUEST_USO4 (54)] Driver can receive USOv4 packets. > @@ -139,6 +141,7 @@ \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} > @@ -1508,6 +1511,12 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi > If the VIRTIO_NET_F_NOTF_COAL feature is negotiated, the driver can > send control commands for dynamically changing the coalescing parameters. > > +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 an enabled transmit/receive virtqueue. > +2. a driver can send a VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET command to a device, and the device > + returns the coalescing parameters of an enabled transmit/receive > virtqueue. Use an enumeration. > + > \begin{note} > The behavior of the device in response to these commands is best-effort: > the device may generate notifications more or less frequently than specified. > @@ -1519,25 +1528,55 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi > le32 max_usecs; > }; > > +struct virtio_net_ctrl_coal_vq { > + le16 vqn; > + le16 reserved; > + struct virtio_net_ctrl_coal coal; > +}; > + > #define VIRTIO_NET_CTRL_NOTF_COAL 6 > #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: > \begin{itemize} > +\item \field{vqn}: The virtqueue number of an enabled transmit or receive virtqueue. > \item \field{max_usecs} for RX: Maximum number of microseconds to delay a RX notification. > \item \field{max_usecs} for TX: Maximum number of microseconds to delay a TX notification. > \item \field{max_packets} for RX: Maximum number of packets to receive before a RX notification. > \item \field{max_packets} for TX: Maximum number of packets to send before a TX notification. > \end{itemize} > > -The class VIRTIO_NET_CTRL_NOTF_COAL has 2 commands: > +\field{vqn} points to an enabled transmit/receive virtqueue, and its value satisfies $ 0 \leq vqn < max_virtqueue_pairs \ast 2 $. > + > +\field{reserved} is reserved and it is ignored by the device. > + > +The class VIRTIO_NET_CTRL_NOTF_COAL has 4 commands: > \begin{enumerate} > -\item VIRTIO_NET_CTRL_NOTF_COAL_TX_SET: set the \field{max_usecs} and \field{max_packets} parameters for all transmit virtqueues. > -\item VIRTIO_NET_CTRL_NOTF_COAL_RX_SET: set the \field{max_usecs} and \field{max_packets} parameters for all receive virtqueues. > +\item VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET: set the \field{max_usecs} and \field{max_packets} parameters for an enabled transmit/receive > + virtqueue whose number is \field{vqn}. > +\item VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET: the device returns the \field{max_usecs} and \field{max_packets} parameters for an enabled > + transmit/receive virtqueue whose number is \field{vqn}. > +\item VIRTIO_NET_CTRL_NOTF_COAL_TX_SET: have the same effect as the VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command repeated for each virtqueue of transmitq1\ldots transmitqN. > +\item VIRTIO_NET_CTRL_NOTF_COAL_RX_SET: have the same effect as the VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command repeated for each virtqueue of receiveq1\ldots receiveqN. > \end{enumerate} > > +If coalescing parameters are being set, the device applies the last coalescing parameters received for a > +virtqueue, regardless of the command used to set the parameters. For example with 2 pairs of virtqueues: > +# Command sequece "sequence" > +Each of the following commands sets \field{max_usecs} and \field{max_packets} parameters for virtqueues. > +\begin{itemize} > +\item Command1: VIRTIO_NET_CTRL_NOTF_COAL_RX_SET sets parameters for virtqueue0 and virtqueue2, and, virtqueue1 and virtqueue3 retain their previous parameter values. > +\item Command2: VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET with \field{vqn} = 0 sets parameters for virtqueue0, and virtqueue2 retains the values from command1. > +\item Command3: VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET with \field{vqn}= 0, the device returns paramters of virtqueue0 set by command2. Missing space before =. > +\item Command4: VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET with \field{vqn} = 1 sets parameters for virtqueue1, and virtqueue3 retains its previous values. > +\item Command5: VIRTIO_NET_CTRL_NOTF_COAL_TX_SET sets parameters for virtqueue1 and virtqueue3, and overrides the values set by command4. > +\item Command6: VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET with \field{vqn}= 1, the device returns paramters of virtqueue1 set by command5. Missing space before =. > +\end{itemize} > + > \subparagraph{Operation}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing / Operation} > > The device sends a used buffer notification once the notification conditions are met and if the notifications are not suppressed as explained in \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Used Buffer Notification Suppression}. > @@ -1585,14 +1624,31 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi > > \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. Too many negatives here. Just "have been negotiated". > + > +A driver MUST ignore the values of coalescing paramters received from VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET, "parameters" Remove the comma? > +if the device returns with VIRTIO_NET_ERR. > > \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. > +Note: VIRTIO_NET_CTRL_NOTF_COAL_VQ_{SET, GET} are exception to it, which must return VIRTIO_NET_ERR if the device was unable to change the parameters. "an exception" > > A device SHOULD NOT send used buffer notifications to the driver if the notifications are suppressed, even if the notification conditions are met. > > +If a virtqueue is disabled, the device MUST clear its parameters configuration, and: > +1. if the device has received a global parameter values sent by VIRTIO_NET_CTRL_NOTF_{RX, TX}_SET: > +after the virtqueue is enabled, its parameters SHOULD be set to the global values. > +2. if the device hasn't received the VIRTIO_NET_CTRL_NOTF_{RX, TX}_SET commands: > +regardless of whether the device has received a VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command, after the > +virtqueue is enabled, its parameters SHOULD be set to 0. Use an enumeration. > + > +When a device receives a virtqueue command to set or return coalescing parameters for the supplied \field{vqn}, > +if the virtqueue is not enabled, the device MUST respond to the command with VIRTIO_NET_ERR. > + > +A device MAY set the coalescing parameter to a value close to a power of 2 value. > + > Upon reset, a device MUST initialize all coalescing parameters to 0. > > \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device -- We're deep in discussion, the party's on mute.
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