On Thu, Jun 20, 2024 at 12:19:05AM +0800, Heng Qi wrote:
> If the device does not respond to a request for a long time,
> then control vq polling elevates CPU utilization, a problem that
> exacerbates with more command requests.
>
> Enabling control vq's irq is advantageous for the guest, and
> this still doesn't support concurrent requests.
>
> Suggested-by: Jason Wang <jasow...@redhat.com>
> Signed-off-by: Heng Qi <hen...@linux.alibaba.com>
> ---
> drivers/net/virtio_net.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index b45f58a902e3..ed10084997d3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -372,6 +372,8 @@ struct virtio_net_ctrl_rss {
> struct control_buf {
> struct virtio_net_ctrl_hdr hdr;
> virtio_net_ctrl_ack status;
> + /* Wait for the device to complete the cvq request. */
> + struct completion completion;
> };
>
> struct virtnet_info {
> @@ -664,6 +666,13 @@ static bool virtqueue_napi_complete(struct napi_struct
> *napi,
> return false;
> }
>
> +static void virtnet_cvq_done(struct virtqueue *cvq)
> +{
> + struct virtnet_info *vi = cvq->vdev->priv;
> +
> + complete(&vi->ctrl->completion);
> +}
> +
> static void skb_xmit_done(struct virtqueue *vq)
> {
> struct virtnet_info *vi = vq->vdev->priv;
> @@ -2724,14 +2733,8 @@ static bool virtnet_send_command_reply(struct
> virtnet_info *vi,
> if (unlikely(!virtqueue_kick(vi->cvq)))
> goto unlock;
>
> - /* Spin for a response, the kick causes an ioport write, trapping
> - * into the hypervisor, so the request should be handled immediately.
> - */
> - while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> - !virtqueue_is_broken(vi->cvq)) {
> - cond_resched();
> - cpu_relax();
> - }
> + wait_for_completion(&ctrl->completion);
> + virtqueue_get_buf(vi->cvq, &tmp);
>
> unlock:
> ok = ctrl->status == VIRTIO_NET_OK;
Hmm no this is not a good idea, code should be robust in case
of spurious interrupts.
Also suprise removal is now broken ...
> @@ -5312,7 +5315,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>
> /* Parameters for control virtqueue, if any */
> if (vi->has_cvq) {
> - callbacks[total_vqs - 1] = NULL;
> + callbacks[total_vqs - 1] = virtnet_cvq_done;
> names[total_vqs - 1] = "control";
> }
>
> @@ -5832,6 +5835,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (vi->has_rss || vi->has_rss_hash_report)
> virtnet_init_default_rss(vi);
>
> + init_completion(&vi->ctrl->completion);
> enable_rx_mode_work(vi);
>
> /* serialize netdev register + virtio_device_ready() with ndo_open() */
> --
> 2.32.0.3.g01195cf9f
