Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Jason Wang]

On 2017å03æ29æ 20:07, Michael S. Tsirkin wrote:
> On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
> > For the socket that exports its skb array, we can use lockless polling
> > to avoid touching spinlock during busy polling.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   drivers/vhost/net.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 53f09f2..41153a3 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
> >   	return len;
> >   }
> >   
> > -static int sk_has_rx_data(struct sock *sk)
> > +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
> >   {
> >   	struct socket *sock = sk->sk_socket;
> >   
> > +	if (rvq->rx_array)
> > +		return !__skb_array_empty(rvq->rx_array);
> > +
> >   	if (sock->ops->peek_len)
> >   		return sock->ops->peek_len(sock);
> >   
> I don't see which patch adds __skb_array_empty.

This is not something new, it was introduced by ad69f35d1dc0a 
("skb_array: array based FIFO for skbs").

Thanks

> > @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
> >   		endtime = busy_clock() + vq->busyloop_timeout;
> >   
> >   		while (vhost_can_busy_poll(&net->dev, endtime) &&
> > -		       !sk_has_rx_data(sk) &&
> > +		       !sk_has_rx_data(rvq, sk) &&
> >   		       vhost_vq_avail_empty(&net->dev, vq))
> >   			cpu_relax();
> >   
> > --
> > 2.7.4