On Thursday, 2023-02-23 at 08:20:34 -05, Michael S. Tsirkin wrote:
> On Thu, Feb 23, 2023 at 11:43:29AM +0000, David Edmondson wrote:
>>
>> On Thursday, 2023-02-23 at 18:52:14 +08, Heng Qi wrote:
>> > Hi, David.
>> >
>> > 在 2023/2/23 下午6:05, David Edmondson 写道:
>> >> On Wednesday, 2023-02-22 at 22:06:32 +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 <[email protected]>
>> >>> Reviewed-by: Xuan Zhuo <[email protected]>
>> >>> ---
>> >>> This patch is on top of Alvaro's latest v7 patch:
>> >>> https://lists.oasis-open.org/archives/virtio-dev/202302/msg00431.html .
>> >>>
>> >>> v6->v7:
>> >>> 1. Clarify the relationship of
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_TX/RX_SET and
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET. @Alvaro Karsz, @Michael S. Tsirkin
>> >>> 2. Remove formula for vqn range. @Parav Pandit
>> >>> 3. Some expressions are clearer. @Parav Pandit, @Michael S.
>> >>> Tsirkin
>> >>>
>> >>> v5->v6:
>> >>> 1. Explain that the device may set a different value than the
>> >>> one passed in by the driver. @David Edmondson
>> >> A couple of things about this:
>> >> - why say "a value close to a power of 2" - couldn't the device pick any
>> >> value it chooses?
>> >
>> > This is just a hint from the spec, it is "MAY", not "MUST" in the
>> > conformance of the device, the device can still set any value it
>> > receives.
>>
>> Okay.
>>
>> > And, since "virtqueue notification coalescing" feature will be used in
>> > the netdim [1] algorithm,
>> > and the coalescing moderation of netdim is roughly as follows, so it
>> > is allowed to give the hint in the spec:
>> > "
>> > #define NET_DIM_RX_EQE_PROFILES { \
>> > {.usec = 1, .pkts = NET_DIM_DEFAULT_RX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 8, .pkts = NET_DIM_DEFAULT_RX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 64, .pkts = NET_DIM_DEFAULT_RX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 128, .pkts = NET_DIM_DEFAULT_RX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 256, .pkts = NET_DIM_DEFAULT_RX_CQ_PKTS_FROM_EQE,} \
>> > }
>> >
>> > #define NET_DIM_RX_CQE_PROFILES { \
>> > {.usec = 2, .pkts = 256,}, \
>> > {.usec = 8, .pkts = 128,}, \
>> > {.usec = 16, .pkts = 64,}, \
>> > {.usec = 32, .pkts = 64,}, \
>> > {.usec = 64, .pkts = 64,} \
>> > }
>> >
>> > #define NET_DIM_TX_EQE_PROFILES { \
>> > {.usec = 1, .pkts = NET_DIM_DEFAULT_TX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 8, .pkts = NET_DIM_DEFAULT_TX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 32, .pkts = NET_DIM_DEFAULT_TX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 64, .pkts = NET_DIM_DEFAULT_TX_CQ_PKTS_FROM_EQE,}, \
>> > {.usec = 128, .pkts = NET_DIM_DEFAULT_TX_CQ_PKTS_FROM_EQE,} \
>> > }
>> >
>> > #define NET_DIM_TX_CQE_PROFILES { \
>> > {.usec = 5, .pkts = 128,}, \
>> > {.usec = 8, .pkts = 64,}, \
>> > {.usec = 16, .pkts = 32,}, \
>> > {.usec = 32, .pkts = 32,}, \
>> > {.usec = 64, .pkts = 32,} \
>> > }
>> > "
>> > [1] https://docs.kernel.org/networking/net_dim.html
>> >
>> >> - I think that we need to be more explicit that the values passed in the
>> >> SET request may not be honoured exactly.
>> >
>> > Yes, there are already examples in the current spec:
>> > "
>> > +When a device receives a command of the VIRTIO_NET_CTRL_NOTF_COAL
>> > class to set a coalescing parameter,
>> > +it may set the parameter to a value close to a power of 2. For example:
>> > +If the device receives \field{max_usecs} = 7 from the
>> > VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command, it may set \field{max_usecs}
>> > = 8 for a given enabled virtqueue.
>> > "
>> > If you find this unclear, do you need more examples or clarification,
>> > or do you have a better way?
>>
>> Explicit is good:
>>
>> When a device receives a command of the VIRTIO_NET_CTRL_NOTF_COAL class
>> to set a coalescing parameter it may choose to use a value different to
>> that specified in the command, for example a power of two value close to
>> the specified parameter.
>
>
> Hmm. This clarification actually belongs in Alvaro's patch btw, no?
> Basically with the best-effort sentence.
Sure.
>> The value chosen by the device can be retrieved
>> using the VIRTIO_NET_CTRL_NOTF_VQ_GET command.
>
> I do however feel that maybe we should not allow any value.
> Values lower than what is specified are definitely ok.
Amusingly, or not, that runs counter to the provided example (setting 7
usecs, getting 8).
>
>> >> - should the chosen value be returned in the SET call? (Not too fussed
>> >> about this, though it may result in an implementation immediately
>> >> calling GET after SET to see what actually happened.)
>> >
>> > As you said, I think we can just call GET to view.
>> >
>> >> - the example which shows how the global and per-VQ set operations
>> >> interact is reasonably worded ("the device responds with coalescing
>> >> parameters of virtqueue1 set by command5"), so that seems okay.
>> >
>> > Yeah.
>> >
>> > Thanks.
>> >
>> >>> v4->v5:
>> >>> 1. Add the correspondence between virtio_net_ctrl_coal and
>> >>> virtio_net_ctrl_coal_vq and control commands. @Michael S. Tsirkin
>> >>> 2. Add read and write attributes for each field. @Michael S.
>> >>> Tsirkin
>> >>> 3. A clearer description of how to set coalescing parameters for
>> >>> vq reset. @Michael S. Tsirkin
>> >>> 4. Fix some syntax errors. @Michael S. Tsirkin, @David Edmondson
>> >>>
>> >>> 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 | 99 ++++++++++++++++++++++++++++++--
>> >>> 1 file changed, 94 insertions(+), 5 deletions(-)
>> >>>
>> >>> diff --git a/device-types/net/description.tex
>> >>> b/device-types/net/description.tex
>> >>> index e71e33b..745e4d9 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 +1511,14 @@ \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:
>> >>> +\begin{itemize}
>> >>> +\item a driver can send a VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command to
>> >>> set coalescing parameters of a given
>> >>> + enabled transmit/receive virtqueue.
>> >>> +\item a driver can send a VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET command to a
>> >>> device, and the device responds with
>> >>> + coalescing parameters of a given enabled transmit/receive
>> >>> virtqueue.
>> >>> +\end{itemize}
>> >>> +
>> >>> \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 +1530,76 @@ \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}
>> >>> +The VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET commands use the
>> >>> +virtio_net_ctrl_coal structure to set \field{max_usecs} and
>> >>> \field{max_packets} for all
>> >>> +transmit/receive virtqueues.
>> >>> +
>> >>> +The VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command uses the
>> >>> virtio_net_ctrl_coal_vq structure
>> >>> +to set \field{max_usecs} and \field{max_packets} for the supplied
>> >>> virtqueue number \field{vqn}.
>> >>> +
>> >>> +The VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET command gets the values of
>> >>> \field{max_usecs} and
>> >>> +\field{max_packets} of the specified virtqueue from the device by
>> >>> setting \field{vqn}
>> >>> +in the virtio_net_ctrl_coal_vq structure.
>> >>> +
>> >>> +# Read/Write attributes for coalescing parameters
>> >>> +\begin{itemize}
>> >>> +\item For commands VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET, \field{max_usecs}
>> >>> + and \field{max_packets} are write-only for a driver.
>> >>> +\item For the command VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET, \field{vqn},
>> >>> \field{reserved}, \field{max_usecs}
>> >>> + and \field{max_packets} are write-only for a driver.
>> >>> +\item For the command VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET, \field{vqn} and
>> >>> \field{reserved} are write-only
>> >>> + for a driver, and, \field{max_usecs} and \field{max_packets} are
>> >>> read-only for the driver.
>> >>> +\end{itemize}
>> >>> +
>> >>> 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{reserved} is reserved and it is ignored by a 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 of setting
>> >>> coalescing parameters 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 of setting
>> >>> coalescing parameters 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 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 coalescing
>> > 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 coalescing 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 responds with coalescing parameters of virtqueue0 set by
>> >>> command2.
>> >>> +\item Command4: VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET with \field{vqn} = 1
>> >>> sets coalescing parameters for virtqueue1, and virtqueue3 retains its
>> >>> previous values.
>> >>> +\item Command5: VIRTIO_NET_CTRL_NOTF_COAL_TX_SET sets coalescing
>> >>> 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 responds with coalescing parameters of virtqueue1 set by
>> >>> command5.
>> >>> +\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}.
>> >>> @@ -1549,6 +1611,15 @@ \subsubsection{Control
>> >>> Virtqueue}\label{sec:Device Types / Network Device / Devi
>> >>> When the device has \field{max_usecs} = 0 or
>> >>> \field{max_packets} = 0, the notification conditions are met after
>> >>> every packet received/sent.
>> >>> +When a device receives a command of the
>> >>> VIRTIO_NET_CTRL_NOTF_COAL class to set a coalescing parameter,
>> >>> +it may set the parameter to a value close to a power of 2. For example:
>> >>> +If the device receives \field{max_usecs} = 7 from the
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command, it may set \field{max_usecs} =
>> >>> 8 for a given enabled virtqueue.
>> >>> +
>> >>> +When the device receives the VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET commands,
>> >>> +it saves the values of coalescing parameters as global values, and the
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command
>> >>> +does not change the global values. If the device is reset, the global
>> >>> values will be set to 0.
>> >>> +When a virtqueue is enabled after virtqueue reset, its coalescing
>> >>> parameters are set to global values.
>> >>> +
>> >>> \subparagraph{RX Example}\label{sec:Device Types / Network Device /
>> >>> Device Operation / Control Virtqueue / Notifications Coalescing / RX
>> >>> Example}
>> >>> If, for example:
>> >>> @@ -1585,11 +1656,29 @@ \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 been negotiated, the driver MUST NOT issue
>> >>> VIRTIO_NET_CTRL_NOTF_COAL commands.
>> >>> +
>> >>> +A driver MUST ignore the values of coalescing parameters received from
>> >>> the VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET command if a device responds 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.
>> >>> +A device SHOULD respond to VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and
> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET commands with VIRTIO_NET_ERR if it
> was not able to change the parameters.
>> >>> +
>> >>> +A device MUST respond to the VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command
>> >>> with VIRTIO_NET_ERR if it was not able to change the parameters.
>> >>> +
>> >>> +A device MUST respond to VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET and
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET commands with VIRTIO_NET_ERR if the
>> >>> given virtqueue is disabled.
>> >>> +
>> >>> +The VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and
>> >>> VIRTIO_NET_CTRL_NOTF_COAL_RX_SET commands set coalescing parameters for
>> >>> all transmit/receive
>> >>> +virtqueues respectively and values of coalescing parameters are
>> >>> recorded as global values by a device.
>> >>> +The device MUST set the global values of coalescing parameters to 0
>> >>> after being reset.
>> >>> +The VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET command sets the coalescing
>> >>> parameters for a given enabled virtqueue without changing the global
>> >>> values.
>> >>> +
>> >>> +After disabling and re-enabling a virtqueue, the device MUST revert
>> >>> coalescing parameters of the virtqueue to the global values.
>> >>> +
>> >>> +A device MAY set the coalescing parameter to a value close to a power
>> >>> of 2 value.
>> >>> +
>> >>> +A device MUST ignore \field{reserved}.
>> >>> A device SHOULD NOT send used buffer notifications to the
>> >>> driver if the notifications are suppressed, even if the
>> >>> notification conditions are met.
>> >
>> >
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>> >
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>> --
>> Come down, come talk to me.
>
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