Re: [PATCH net-next 2/3] virtio-net: batch dim request

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在 2024/1/17 上午3:49, Simon Horman 写道:
On Tue, Jan 16, 2024 at 09:11:32PM +0800, Heng Qi wrote:
Currently, when each time the driver attempts to update the coalescing
parameters for a vq, it needs to kick the device.
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.

When large-queue devices issue multiple requests and kick the device
frequently, this often interrupt the work of the device-side CPU.
In addition, each vq request is processed separately, causing more
delays for the 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.

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@xxxxxxxxxxxxxxx>
Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>

@@ -3546,16 +3552,32 @@ static void virtnet_rx_dim_work(struct work_struct *work)
  		update_moder = net_dim_get_rx_moderation(dim->mode, dim->profile_ix);
  		if (update_moder.usec != rq->intr_coal.max_usecs ||
  		    update_moder.pkts != rq->intr_coal.max_packets) {
-			err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, qnum,
-							       update_moder.usec,
-							       update_moder.pkts);
-			if (err)
-				pr_debug("%s: Failed to send dim parameters on rxq%d\n",
-					 dev->name, qnum);
-			dim->state = DIM_START_MEASURE;
+			coal->coal_vqs[j].vqn = cpu_to_le16(rxq2vq(i));
+			coal->coal_vqs[j].coal.max_usecs = cpu_to_le32(update_moder.usec);
+			coal->coal_vqs[j].coal.max_packets = cpu_to_le32(update_moder.pkts);
+			rq->intr_coal.max_usecs = update_moder.usec;
+			rq->intr_coal.max_packets = update_moder.pkts;
+			j++;
+ if (!j)
+		goto ret;
+	coal->num_entries = cpu_to_le32(j);
+	sg_init_one(&sgs, coal, sizeof(struct virtnet_batch_coal) +
+		    j * sizeof(struct virtio_net_ctrl_coal_vq));
+	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
+				  &sgs))
+		dev_warn(&vi->vdev->dev, "Failed to add dim command\n.");
+	for (i = 0; i < j; i++) {
+		rq = &vi->rq[(coal->coal_vqs[i].vqn) / 2];
Hi Heng Qi,

The type of .vqn is __le16, but here it is used as an
integer in host byte order. Perhaps this should be (completely untested!):

		rq = &vi->rq[le16_to_cpu(coal->coal_vqs[i].vqn) / 2];

Hi Simon,

Thanks for the catch, I will check this out.

+		rq->dim.state = DIM_START_MEASURE;
+	}

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