Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling
On 2017年03月30日 10:33, Michael S. Tsirkin wrote: On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote: On 2017年03月29日 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 --- 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 Same comment about a compiler barrier applies then. Ok, rethink about this, since skb_array could be resized, using lockless version seems wrong. For the comment of using compiler barrier, caller (vhost_net_rx_peek_head_len) uses cpu_relax(). But I haven't figured out why a compiler barrier is needed here. Could you please explain? 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
Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling
On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote: > > > On 2017年03月29日 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 > > > --- > > > 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 Same comment about a compiler barrier applies then. > > > > > @@ -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
Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling
On 2017年03月29日 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 --- 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
Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling
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 > --- > 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. > @@ -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
[PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling
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 --- 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); @@ -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