Re: [PATCH net-next 3/3] virtio-net: reduce the CPU consumption of dim worker

[Heng Qi]

在 2024/1/17 上午3:56, Simon Horman 写道:

On Tue, Jan 16, 2024 at 09:11:33PM +0800, Heng Qi wrote:

Accumulate multiple request commands to kick the device once,
and obtain the processing results of the corresponding commands
asynchronously. The batch command method is used to optimize the
CPU overhead of the DIM worker caused by the guest being busy
waiting for the command response result.

On an 8-queue device, without this patch, the guest cpu overhead
due to waiting for cvq could be 10+% and above. With this patch,
the corresponding overhead is basically invisible.

Signed-off-by: Heng Qi <hen...@linux.alibaba.com>

...

@@ -3520,22 +3568,99 @@ static int virtnet_send_notf_coal_vq_cmds(struct 
virtnet_info *vi,
        return 0;
  }

+static bool virtnet_add_dim_command(struct virtnet_info *vi,

+                                   struct virtnet_batch_coal *ctrl)
+{
+       struct scatterlist *sgs[4], hdr, stat, out;
+       unsigned out_num = 0;
+       int ret;
+
+       /* Caller should know better */
+       BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ));
+
+       ctrl->hdr.class = VIRTIO_NET_CTRL_NOTF_COAL;
+       ctrl->hdr.cmd = VIRTIO_NET_CTRL_NOTF_COAL_VQS_SET;
+
+       /* Add header */
+       sg_init_one(&hdr, &ctrl->hdr, sizeof(ctrl->hdr));
+       sgs[out_num++] = &hdr;
+
+       /* Add body */
+       sg_init_one(&out, &ctrl->num_entries, sizeof(ctrl->num_entries) +
+                   ctrl->num_entries * sizeof(struct virtnet_coal_entry));

Hi Heng Qi,

I am a bit confused.
With this series applied on top of net-next
struct virtnet_coal_entry doesn't seem to exist.

Hi Simon,

It should be struct virtio_net_ctrl_coal_vq.

Thanks.

+       sgs[out_num++] = &out;
+
+       /* Add return status. */
+       ctrl->status = VIRTIO_NET_OK;
+       sg_init_one(&stat, &ctrl->status, sizeof(ctrl->status));
+       sgs[out_num] = &stat;
+
+       BUG_ON(out_num + 1 > ARRAY_SIZE(sgs));
+       ret = virtqueue_add_sgs(vi->cvq, sgs, out_num, 1, ctrl, GFP_ATOMIC);
+       if (ret < 0) {
+               dev_warn(&vi->vdev->dev, "Failed to add sgs for command vq: 
%d\n.", ret);
+               return false;
+       }
+
+       virtqueue_kick(vi->cvq);
+
+       ctrl->usable = false;
+       vi->cvq_cmd_nums++;
+
+       return true;
+}

...