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Subject: Re: [virtio-comment] Re: [PATCH v7] virtio-net: support the virtqueue coalescing moderation
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. > > > > å 2023/2/23 äå6:05, David Edmondson åé: > >> 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 <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 . > >>> > >>> 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]Â 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. > 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. > >> - 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. > > > > > > This publicly archived list offers a means to provide input to the > > OASIS Virtual I/O Device (VIRTIO) TC. > > > > In order to verify user consent to the Feedback License terms and > > to minimize spam in the list archive, subscription is required > > before posting. > > > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > > List help: virtio-comment-help@lists.oasis-open.org > > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > > Committee: https://www.oasis-open.org/committees/virtio/ > > Join OASIS: https://www.oasis-open.org/join/ > -- > Come down, come talk to me.
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