netdev - Re: [PATCH net-next V5 2/3] vhost

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Date:   Wed, 18 Jan 2017 19:03:16 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, stephen@...workplumber.org, wexu@...hat.com,
        stefanha@...hat.com
Subject: Re: [PATCH net-next V5 2/3] vhost_net: tx batching

On Wed, Jan 18, 2017 at 03:02:02PM +0800, Jason Wang wrote:
> This patch tries to utilize tuntap rx batching by peeking the tx
> virtqueue during transmission, if there's more available buffers in
> the virtqueue, set MSG_MORE flag for a hint for backend (e.g tuntap)
> to batch the packets.
> 
> Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> ---
>  drivers/vhost/net.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 5dc3465..c42e9c3 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -351,6 +351,15 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
>  	return r;
>  }
>  
> +static bool vhost_exceeds_maxpend(struct vhost_net *net)
> +{
> +	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
> +	struct vhost_virtqueue *vq = &nvq->vq;
> +
> +	return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV
> +		== nvq->done_idx;
> +}
> +
>  /* Expects to be always run from workqueue - which acts as
>   * read-size critical section for our kind of RCU. */
>  static void handle_tx(struct vhost_net *net)
> @@ -394,8 +403,7 @@ static void handle_tx(struct vhost_net *net)
>  		/* If more outstanding DMAs, queue the work.
>  		 * Handle upend_idx wrap around
>  		 */
> -		if (unlikely((nvq->upend_idx + vq->num - VHOST_MAX_PEND)
> -			      % UIO_MAXIOV == nvq->done_idx))
> +		if (unlikely(vhost_exceeds_maxpend(net)))
>  			break;
>  
>  		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
> @@ -454,6 +462,16 @@ static void handle_tx(struct vhost_net *net)
>  			msg.msg_control = NULL;
>  			ubufs = NULL;
>  		}
> +
> +		total_len += len;
> +		if (total_len < VHOST_NET_WEIGHT &&
> +		    !vhost_vq_avail_empty(&net->dev, vq) &&
> +		    likely(!vhost_exceeds_maxpend(net))) {
> +			msg.msg_flags |= MSG_MORE;
> +		} else {
> +			msg.msg_flags &= ~MSG_MORE;
> +		}
> +
>  		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>  		err = sock->ops->sendmsg(sock, &msg, len);
>  		if (unlikely(err < 0)) {
> @@ -472,7 +490,6 @@ static void handle_tx(struct vhost_net *net)
>  			vhost_add_used_and_signal(&net->dev, vq, head, 0);
>  		else
>  			vhost_zerocopy_signal_used(net, vq);
> -		total_len += len;
>  		vhost_net_tx_packet(net);
>  		if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
>  			vhost_poll_queue(&vq->poll);
> -- 
> 2.7.4