netdev - Re: [PATCH net-next v8 3/7] net: vhost: factor out busy polling logic to vhost_net_busy

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Date:   Tue, 21 Aug 2018 11:15:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     xiangxia.m.yue@...il.com, mst@...hat.com,
        makita.toshiaki@....ntt.co.jp
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v8 3/7] net: vhost: factor out busy polling logic
 to vhost_net_busy_poll()



On 2018年08月19日 20:11, xiangxia.m.yue@...il.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@...il.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.
>
> To avoid duplicate codes, introduce the helper functions:
> * sock_has_rx_data(changed from sk_has_rx_data)
> * vhost_net_busy_poll_try_queue
>
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> ---
>   drivers/vhost/net.c | 111 +++++++++++++++++++++++++++++++++-------------------
>   1 file changed, 71 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 32c1b52..453c061 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -440,6 +440,75 @@ static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq)
>   	nvq->done_idx = 0;
>   }
>   
> +static int sock_has_rx_data(struct socket *sock)
> +{
> +	if (unlikely(!sock))
> +		return 0;
> +
> +	if (sock->ops->peek_len)
> +		return sock->ops->peek_len(sock);
> +
> +	return skb_queue_empty(&sock->sk->sk_receive_queue);
> +}
> +
> +static void vhost_net_busy_poll_try_queue(struct vhost_net *net,
> +					  struct vhost_virtqueue *vq)
> +{
> +	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);
> +	}
> +}
> +
> +static void vhost_net_busy_poll(struct vhost_net *net,
> +				struct vhost_virtqueue *rvq,
> +				struct vhost_virtqueue *tvq,
> +				bool *busyloop_intr,
> +				bool poll_rx)
> +{
> +	unsigned long busyloop_timeout;
> +	unsigned long endtime;
> +	struct socket *sock;
> +	struct vhost_virtqueue *vq = poll_rx ? tvq : rvq;
> +
> +	mutex_lock_nested(&vq->mutex, poll_rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX);
> +	vhost_disable_notify(&net->dev, vq);
> +	sock = rvq->private_data;
> +
> +	busyloop_timeout = poll_rx ? rvq->busyloop_timeout:
> +				     tvq->busyloop_timeout;
> +
> +	preempt_disable();
> +	endtime = busy_clock() + busyloop_timeout;
> +
> +	while (vhost_can_busy_poll(endtime)) {
> +		if (vhost_has_work(&net->dev)) {
> +			*busyloop_intr = true;
> +			break;
> +		}
> +
> +		if ((sock_has_rx_data(sock) &&
> +		     !vhost_vq_avail_empty(&net->dev, rvq)) ||
> +		    !vhost_vq_avail_empty(&net->dev, tvq))
> +			break;
> +
> +		cpu_relax();
> +	}
> +
> +	preempt_enable();
> +
> +	if (poll_rx)
> +		vhost_net_busy_poll_try_queue(net, tvq);
> +	else if (sock_has_rx_data(sock))
> +		vhost_net_busy_poll_try_queue(net, rvq);

This could be simplified like:

if (poll_rx || sock_has_rx_data(sock))
     vhost_net_busy_poll_try_queue(net, vq);

Thanks

> +	else /* On tx here, sock has no rx data. */
> +		vhost_enable_notify(&net->dev, rvq);
> +
> +	mutex_unlock(&vq->mutex);
> +}
> +
>   static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
>   				    struct vhost_net_virtqueue *nvq,
>   				    unsigned int *out_num, unsigned int *in_num,
> @@ -753,16 +822,6 @@ 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 int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
>   				      bool *busyloop_intr)
>   {
> @@ -770,41 +829,13 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
>   	struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
>   	struct vhost_virtqueue *rvq = &rnvq->vq;
>   	struct vhost_virtqueue *tvq = &tnvq->vq;
> -	unsigned long uninitialized_var(endtime);
>   	int len = peek_head_len(rnvq, sk);
>   
> -	if (!len && tvq->busyloop_timeout) {
> +	if (!len && rvq->busyloop_timeout) {
>   		/* Flush batched heads first */
>   		vhost_net_signal_used(rnvq);
>   		/* Both tx vq and rx socket were polled here */
> -		mutex_lock_nested(&tvq->mutex, VHOST_NET_VQ_TX);
> -		vhost_disable_notify(&net->dev, tvq);
> -
> -		preempt_disable();
> -		endtime = busy_clock() + tvq->busyloop_timeout;
> -
> -		while (vhost_can_busy_poll(endtime)) {
> -			if (vhost_has_work(&net->dev)) {
> -				*busyloop_intr = true;
> -				break;
> -			}
> -			if ((sk_has_rx_data(sk) &&
> -			     !vhost_vq_avail_empty(&net->dev, rvq)) ||
> -			    !vhost_vq_avail_empty(&net->dev, tvq))
> -				break;
> -			cpu_relax();
> -		}
> -
> -		preempt_enable();
> -
> -		if (!vhost_vq_avail_empty(&net->dev, tvq)) {
> -			vhost_poll_queue(&tvq->poll);
> -		} else if (unlikely(vhost_enable_notify(&net->dev, tvq))) {
> -			vhost_disable_notify(&net->dev, tvq);
> -			vhost_poll_queue(&tvq->poll);
> -		}
> -
> -		mutex_unlock(&tvq->mutex);
> +		vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, true);
>   
>   		len = peek_head_len(rnvq, sk);
>   	}