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Subject: Re: [virtio-comment] RE: [PATCH v3] virtio-net: support setting coalescing params for multiple vqs
å 2024/1/30 äå2:05, Parav Pandit åé:
Hi Heng,From: Heng Qi <hengqi@linux.alibaba.com> Sent: Tuesday, January 30, 2024 10:15 AM To: virtio-comment@lists.oasis-open.org Cc: Jason Wang <jasowang@redhat.com>; Michael S. Tsirkin <mst@redhat.com>; Xuan Zhuo <xuanzhuo@linux.alibaba.com>; Parav Pandit <parav@nvidia.com> Subject: [PATCH v3] virtio-net: support setting coalescing params for multiple vqs Currently, when each time the driver attempts to update the coalescing parameters for a vq, it needs to kick the device and wait for the ctrlq response to return. The following path is observed: 1. Driver kicks the device; 2. After the device receives the kick, CPU scheduling occurs and DMA multiple buffers multiple times; 3. The device completes processing and replies with a response. Since Linux ctrlq currently cannot add commands in batches, it can only process one request synchronously at a time.It can. Please refactor the kernel code to not depend on OS global rtnl lock. This cannot be the motivation for spec patch discussed in v2 time.
Hi Parav,I don't think this is related to the OS global rtnl_lock. The purpose of removing rtnl_lock is to better support multi-nics OS. I think you're referring to having controlq handle things asynchronously (e.g. batch add commands), and if asynchronous handling is solved, yes, the "kicks" motivation needs to be removed. The remaining motivation is that the device CPU needs to frequently wait for each requested DMA to complete. The more requests there are, the less efficient the device responds.
When a large-queue driver want to issue multiple requests, the subsequent request must wait for the previous request to be processed before it can be sent: 1. The driver kicks the device frequently, this often interrupt the work of the device-side CPU. In addition, each vq request 2. Each request is pipelined and there can always be only one request in the pipeline, causing more delays for the device-side CPU to wait for the DMA request to complete. These interruptions and overhead will strain the CPU responsible for controlling the path of the DPU, especially in multi-device and large-queue scenarios.Please remove above line as you acked below that those driver notifications are ignored by the device in [1]. [1] https://lists.oasis-open.org/archives/virtio-comment/202401/msg00132.html
Please see the above reply.
To solve the above problems, we internally tried batch request, which merges requests from multiple queues and sends them at once. We conservatively tested 8 queue commands and sent them together. The DPU processing efficiency can be improved by 8 times, which greatly eases the DPU's support for multi- device and multi-queue DIM. Suggested-by: Xiaoming Zhao <zxm377917@alibaba-inc.com> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com> --- v2->v3: 1. Update some descriptions. @ Michael 2. virtio_net_ctrl_mrg_coal_vq -> virtnet_ctrl_mrg_coal_vq 3. Reword the commit log. v1->v2: Updated commit log. Due to sensitivity, sorry that can not give v1->the absolute value directly. @Michael device-types/net/description.tex | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git a/device-types/net/description.tex b/device- types/net/description.tex index aff5e08..dbca203 100644 --- a/device-types/net/description.tex +++ b/device-types/net/description.tex @@ -1667,8 +1667,8 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi for notification coalescing. If the VIRTIO_NET_F_VQ_NOTF_COAL feature is negotiated, the driver can - send commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET -for virtqueue notification coalescing. +send commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET, +VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET for virtqueue notification coalescing. \begin{lstlisting} struct virtio_net_ctrl_coal { @@ -1682,11 +1682,17 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi struct virtio_net_ctrl_coal coal; }; +struct virtnet_ctrl_mrg_coal_vq {Since this doing at batch level, ctrl_coal_vq_batch or ctrl_coal_vqs_batch seems better name.
OK. It's a better name.
+ le16 num_entries; /* indicates number of valid entries */ + struct virtio_net_ctrl_coal_vq entries[]; }; + #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 + #define VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET 4A new feature bit is needed as the driver does not know if all the devices support this command or not.
Well, 1.3 is still not released, if the device wants to support dim better, they should update the device.
Then if you suggest a new feature bit, I will add it in the next version.
For example, some device does not support VQS_SET command. The device is already out that supports notification features per VQ (without coalescing support) and does not plan to support coalescing because OS level enqueue command is optimal for it like rest of the tx and rx q.
Even though ctrlq can do like txq/rxq, for example 256 requests are batched, so the device only needs to process a single request, which is friendly to device. Then it can effectively handle requests
from other VMs, perform software forwarding, etc. Thanks, Heng
\end{lstlisting} Coalescing parameters: @@ -1706,6 +1712,7 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi \item For the command VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET, the structure virtio_net_ctrl_coal_vq is write-only for the driver. \item For the command VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET, \field{vq_index} and \field{reserved} are write-only for the driver, and the structure virtio_net_ctrl_coal is read-only for the driver. +\item For the command VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET, the structure virtnet_ctrl_mrg_coal_vq is write-only for the driver. \end{itemize} The class VIRTIO_NET_CTRL_NOTF_COAL has the following commands: @@ -1716,6 +1723,9 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi for an enabled transmit/receive virtqueue whose index is \field{vq_index}. \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 index is \field{vq_index}. +\item VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET: use the structure virtnet_ctrl_mrg_coal_vq to set the \field{max_usecs} and \field{max_packets} parameters + for \field{num_entries} enabled transmit/receive virtqueues. The corresponding index value + of each configured virtqueue is \field{vq_index}. \end{enumerate} The device may generate notifications more or less frequently than specified by set commands of the VIRTIO_NET_CTRL_NOTF_COAL class. @@ -1782,9 +1792,13 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi The driver MUST set \field{vq_index} to the virtqueue index of an enabled transmit or receive virtqueue. +The driver MUST set \field{num_entries} to a non-zero value and MUST +NOT set \field{num_entries} to a value greater than the number of enabled transmit and receive virtqueues. + The driver MUST have negotiated the VIRTIO_NET_F_NOTF_COAL feature when issuing commands VIRTIO_NET_CTRL_NOTF_COAL_TX_SET and VIRTIO_NET_CTRL_NOTF_COAL_RX_SET. -The driver MUST have negotiated the VIRTIO_NET_F_VQ_NOTF_COAL feature when issuing commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET. +The driver MUST have negotiated the VIRTIO_NET_F_VQ_NOTF_COAL feature +when issuing commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET, VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET. The driver MUST ignore the values of coalescing parameters received from the VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET command if the device responds with VIRTIO_NET_ERR. @@ -1794,10 +1808,12 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi The 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. -The 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. +The device MUST respond to VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET and +VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET commands with VIRTIO_NET_ERR if it +was not able to change some of the coalescing parameters. In this case, all of the parameters MUST remain unchanged, for all virtqueues. -The 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 designated virtqueue is not an enabled transmit or receive virtqueue. +The device MUST respond to VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET, +VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET commands with VIRTIO_NET_ERR if the designated virtqueue is not an enabled transmit or receive virtqueue. Upon disabling and re-enabling a transmit virtqueue, the device MUST set the coalescing parameters of the virtqueue to those configured through the VIRTIO_NET_CTRL_NOTF_COAL_TX_SET command, or, if the driver did not set any TX coalescing parameters, to 0. -- 1.8.3.1This 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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