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Subject: Re: [virtio-comment] Re: [PATCH v6] virtio-net: support the virtqueue coalescing moderation
å 2023/2/22 äå2:29, Michael S. Tsirkin åé:
On Wed, Feb 22, 2023 at 04:13:06AM +0000, Parav Pandit wrote:From: Heng Qi <hengqi@linux.alibaba.com> Sent: Tuesday, February 21, 2023 10:22 PM +\item[VIRTIO_NET_F_VQ_NOTF_COAL(52)] Device supports virtqueue notification coalescing. +s/notification/notifications should be plural as multiple notifications are coalesced like the below description of VIRTIO_NET_F_NOTF_COAL.Hmm nope - this is the "reduced relative" construct. It's always in a singular form. The full form would be "coalescing of notifications of virtqueues" and that indeed would use a plural form. But technical writing is usually using the reduced relative form.\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},Virtio spec is using vq number and vq index terminology interchangeably. For example, a new patch about admin vq, uses aq_start_index. MMIO device has vq_index register too. I am inclined to vq_index given current state of spec[mst@tuck virtio]$ git grep vq_index|wc -l 0and new additions by Michael.admin vq? Good point, I will change that to vqn too.Michael, Can you please suggest vqn or vq_index to use?[mst@tuck virtio]$ git grep vqn|wc -l 5 I'd say vqn has precedent.\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 a driver.Remove this trailing "for a driver", it is a duplicate.Nope it's required, without it, it's unclear which side is doing reading and which writing. Unfortunate that it's a bit verbose but we don't have better terms in the spec right now.+\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{vqn} points to an enabled transmit/receive virtqueue, and its value satisfies $ 0 \leq vqn < max_virtqueue_pairs \ast 2 $. +This calculation description is not needed here. It is covered somewhere else.I agree.+\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 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 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 +1611,16 @@ \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 reset, its coalescing parameters are set to the global values. +A VQ reset operation disables (or destroys) the VQ in the device. Hence, a vq under reset doesn't have any valid parameters. Therefore, above wording should be, When a virtqueue is enabled after it is reset, its coalescing parameters are set to global values as configured by VIRTIO_NET_CTRL_NOTF_COAL_TX_SET or VIRTIO_NET_CTRL_NOTF_COAL_RX_SET.Right though this repeats "it" twice. At which point the second it becomes slightly confusing. Not too bad but ""enabled after virtqueue reset" would address this.
Ok, I'll modify this. Thanks.
\subparagraph{RX Example}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Notifications Coalescing / RX Example} If, for example: @@ -1585,11 +1657,29 @@ \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. -- 2.19.1.6.gb485710bThis 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/
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