Re: [PATCH net-next v4 3/4] net: vhost: factor out busy polling logic to vhost_net_busy_poll()

[Jason Wang <jasowang@redhat.com>]

On 2018年07月02日 20:57, xiangxia.m.yue@gmail.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>
> Factor out generic busy polling logic and will be
> used for in tx path in the next patch. And with the patch,
> qemu can set differently the busyloop_timeout for rx queue.
>
> Signed-off-by: Tonghao Zhang <zhangtonghao@didichuxing.com>
> ---
>   drivers/vhost/net.c | 94 +++++++++++++++++++++++++++++++----------------------
>   1 file changed, 55 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 62bb8e8..2790959 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -429,6 +429,52 @@ static int vhost_net_enable_vq(struct vhost_net *n,
>   	return vhost_poll_start(poll, sock->file);
>   }
>   
> +static int sk_has_rx_data(struct sock *sk)
> +{
> +	struct socket *sock = sk->sk_socket;
> +
> +	if (sock->ops->peek_len)
> +		return sock->ops->peek_len(sock);
> +
> +	return skb_queue_empty(&sk->sk_receive_queue);
> +}
> +
> +static void vhost_net_busy_poll(struct vhost_net *net,
> +				struct vhost_virtqueue *rvq,
> +				struct vhost_virtqueue *tvq,
> +				bool rx)
> +{
> +	unsigned long uninitialized_var(endtime);
> +	unsigned long busyloop_timeout;
> +	struct socket *sock;
> +	struct vhost_virtqueue *vq = rx ? tvq : rvq;
> +
> +	mutex_lock_nested(&vq->mutex, rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX);
> +
> +	vhost_disable_notify(&net->dev, vq);
> +	sock = rvq->private_data;
> +	busyloop_timeout = rx ? rvq->busyloop_timeout : tvq->busyloop_timeout;
> +
> +	preempt_disable();
> +	endtime = busy_clock() + busyloop_timeout;
> +	while (vhost_can_busy_poll(tvq->dev, endtime) &&
> +	       !(sock && sk_has_rx_data(sock->sk)) &&
> +	       vhost_vq_avail_empty(tvq->dev, tvq))
> +		cpu_relax();
> +	preempt_enable();
> +
> +	if ((rx && !vhost_vq_avail_empty(&net->dev, vq)) ||
> +	    (!rx && (sock && sk_has_rx_data(sock->sk)))) {
> +		vhost_poll_queue(&vq->poll);
> +	} else if (unlikely(vhost_enable_notify(&net->dev, vq))) {

One last question, do we need this for rx? This check will be always 
true under light or medium load.

Thanks

> +		vhost_disable_notify(&net->dev, vq);
> +		vhost_poll_queue(&vq->poll);
> +	}
> +
> +	mutex_unlock(&vq->mutex);
> +}
> +
> +
>   static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
>   				    struct vhost_virtqueue *vq,
>   				    struct iovec iov[], unsigned int iov_size,
> @@ -621,16 +667,6 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
>   	return len;
>   }
>   
> -static int sk_has_rx_data(struct sock *sk)
> -{
> -	struct socket *sock = sk->sk_socket;
> -
> -	if (sock->ops->peek_len)
> -		return sock->ops->peek_len(sock);
> -
> -	return skb_queue_empty(&sk->sk_receive_queue);
> -}
> -
>   static void vhost_rx_signal_used(struct vhost_net_virtqueue *nvq)
>   {
>   	struct vhost_virtqueue *vq = &nvq->vq;
> @@ -645,39 +681,19 @@ static void vhost_rx_signal_used(struct vhost_net_virtqueue *nvq)
>   
>   static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
>   {
> -	struct vhost_net_virtqueue *rvq = &net->vqs[VHOST_NET_VQ_RX];
> -	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
> -	struct vhost_virtqueue *vq = &nvq->vq;
> -	unsigned long uninitialized_var(endtime);
> -	int len = peek_head_len(rvq, sk);
> +	struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
> +	struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
>   
> -	if (!len && vq->busyloop_timeout) {
> -		/* Flush batched heads first */
> -		vhost_rx_signal_used(rvq);
> -		/* Both tx vq and rx socket were polled here */
> -		mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_TX);
> -		vhost_disable_notify(&net->dev, vq);
> +	int len = peek_head_len(rnvq, sk);
>   
> -		preempt_disable();
> -		endtime = busy_clock() + vq->busyloop_timeout;
> -
> -		while (vhost_can_busy_poll(&net->dev, endtime) &&
> -		       !sk_has_rx_data(sk) &&
> -		       vhost_vq_avail_empty(&net->dev, vq))
> -			cpu_relax();
> -
> -		preempt_enable();
> -
> -		if (!vhost_vq_avail_empty(&net->dev, vq))
> -			vhost_poll_queue(&vq->poll);
> -		else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> -			vhost_disable_notify(&net->dev, vq);
> -			vhost_poll_queue(&vq->poll);
> -		}
> +	if (!len && rnvq->vq.busyloop_timeout) {
> +		/* Flush batched heads first */
> +		vhost_rx_signal_used(rnvq);
>   
> -		mutex_unlock(&vq->mutex);
> +		/* Both tx vq and rx socket were polled here */
> +		vhost_net_busy_poll(net, &rnvq->vq, &tnvq->vq, true);
>   
> -		len = peek_head_len(rvq, sk);
> +		len = peek_head_len(rnvq, sk);
>   	}
>   
>   	return len;