On Thu, Apr 25, 2024 at 8:59 PM Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> wrote:
>
> Control vq polling request results consume more CPU.
> Especially when dim issues more control requests to the device,
> it's beneficial to the guest to enable control vq's irq.
>
> Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
> Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 45 ++++++++++++++++++++++++++++++----------
> 1 file changed, 34 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index a4d3c76654a4..79a1b30c173c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -287,6 +287,12 @@ struct virtnet_info {
> bool has_cvq;
> struct mutex cvq_lock;
>
> + /* Wait for the device to complete the request */
> + struct completion completion;
> +
> + /* Work struct for acquisition of cvq processing results. */
> + struct work_struct get_cvq;
> +
> /* Host can handle any s/g split between our header and packet data */
> bool any_header_sg;
>
> @@ -520,6 +526,13 @@ 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;
> +
> + schedule_work(&vi->get_cvq);
> +}
> +
> static void skb_xmit_done(struct virtqueue *vq)
> {
> struct virtnet_info *vi = vq->vdev->priv;
> @@ -2036,6 +2049,20 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
> return !oom;
> }
>
> +static void virtnet_get_cvq_work(struct work_struct *work)
> +{
> + struct virtnet_info *vi =
> + container_of(work, struct virtnet_info, get_cvq);
> + unsigned int tmp;
> + void *res;
> +
> + mutex_lock(&vi->cvq_lock);
> + res = virtqueue_get_buf(vi->cvq, &tmp);
> + if (res)
> + complete(&vi->completion);
> + mutex_unlock(&vi->cvq_lock);
> +}
> +
> static void skb_recv_done(struct virtqueue *rvq)
> {
> struct virtnet_info *vi = rvq->vdev->priv;
> @@ -2531,7 +2558,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> struct scatterlist *out)
> {
> struct scatterlist *sgs[4], hdr, stat;
> - unsigned out_num = 0, tmp;
> + unsigned out_num = 0;
> int ret;
>
> /* Caller should know better */
> @@ -2566,16 +2593,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> return vi->ctrl->status == VIRTIO_NET_OK;
> }
>
> - /* 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();
> - }
> -
> mutex_unlock(&vi->cvq_lock);
> +
> + wait_for_completion(&vi->completion);
> +
A question here, can multiple cvq requests be submitted to the device?
If yes, what happens if the device completes them out of order?
Thanks
> return vi->ctrl->status == VIRTIO_NET_OK;
> }
>
> @@ -4433,7 +4454,7 @@ 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";
> }
>
> @@ -4952,6 +4973,8 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (vi->has_rss || vi->has_rss_hash_report)
> virtnet_init_default_rss(vi);
>
> + INIT_WORK(&vi->get_cvq, virtnet_get_cvq_work);
> + init_completion(&vi->completion);
> enable_rx_mode_work(vi);
>
> /* serialize netdev register + virtio_device_ready() with ndo_open() */
> --
> 2.32.0.3.g01195cf9f
>
