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Subject: Re: [virtio-dev] RE: [PATCH v10] virtio-net: support the virtqueue coalescing moderation
å 2023/3/2 äå10:48, Parav Pandit åé:
From: Heng Qi <hengqi@linux.alibaba.com> Sent: Wednesday, March 1, 2023 9:10 AM 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.[..]+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} +Maybe I missed the conversation while I was sick.
I hope you'll be all right very soon.
I remember we discussed that instead of mentioning each individual field, better to describe the whole structure being read-only or write-only.
Consider the following scenarios:1. A read-only field of the structure virtio_net_ctrl_coal is extended for CTRL_NOTF_COAL_RX/TX_SET to get some extra information 2. \field{reserved} of the structure virtio_net_ctrl_coal_vq is reused by CTRL_NOTF_COAL_VQ_SET, and changed from write-only to read-only These cases still need to unpack the structure to describe it with fields, and if we now use field descriptions, we can be satisfied with minimal changes.
+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_TX_SET: use the structure virtio_net_ctrl_coal to set the \field{max_usecs} and \field{max_packets} parameters for all transmit virtqueues. +\item VIRTIO_NET_CTRL_NOTF_COAL_RX_SET: use the structure virtio_net_ctrl_coal to set the \field{max_usecs} and \field{max_packets} parameters for all receive virtqueues. +\item VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET: use the structure virtio_net_ctrl_coal_vq to 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: use the structure virtio_net_ctrl_coal_vq to get the \field{max_usecs} and \field{max_packets} parameters + for an enabled transmit/receive virtqueue whose number is \field{vqn}. \end{enumerate} +\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. +\end{note} +Michael, Why this should be a note? Shouldn't it be a normative line in the device requirements?+If coalescing parameters are being set, the device applies the last +coalescing parameters received for a virtqueue, regardless of thes/received/set to match the if condition wording and regardless sentence after.
Ok. I'll modify it.
+command used to set the parameters. Use the following command sequence with 2 pairs of virtqueues as an example: +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} + +Upon disabling and re-enabling the transmit virtqueue, the device will +set the coalescing parameters of the virtqueue to those configured through the VIRTIO_NET_CTRL_NOTF_COAL_TX_SET command, or to 0 if the command did not set any TX coalescing parameters. + +Upon disabling and re-enabling the receive virtqueue, the device will +set the coalescing parameters of the virtqueue to those configured through the VIRTIO_NET_CTRL_NOTF_COAL_RX_SET command, or to 0 if the command did not set any RX coalescing parameters. +Looks good, however you have well covered in the device normative statements. So possibly it can be removed from here.
I tend to keep this, as we have done in the past, we can have normative descriptions and the corresponding non-normative descriptions.
Thanks.
\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}. @@ -1585,11 +1637,25 @@ \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. +A driver MUST negotiate the VIRTIO_NET_F_NOTF_COAL feature before issuing commands VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and VIRIO_NET_CTRL_NOTF_COAL_RX_SET. + +A driver MUST negotiate the VIRTIO_NET_F_VQ_NOTF_COAL feature before issuing commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET and VIRIO_NET_CTRL_NOTF_COAL_VQ_GET. + +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 MUST ignore \field{reserved}. + +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. + +After disabling and re-enabling a transmit/receive virtqueue, the +device MUST set coalescing parameters of the virtqueue to those +configured using the VIRTIO_NET_CTRL_NOTF_COAL_TX_SET/VIRTIO_NET_CTRL_NOTF_COAL_RX_S ET command, or, if the command did not configure TX/RX coalescing parameters, to 0. 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.gb485710bRest looks good to me. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
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