Re: [PATCH V3 1/2] vhost_net: stop polling socket during rx processing

Michael S. Tsirkin
2016-06-07T12:23:13Z

On Wed, Jun 01, 2016 at 01:56:33AM -0400, Jason Wang wrote:
> We don't stop rx polling socket during rx processing, this will lead
> unnecessary wakeups from under layer net devices (E.g
> sock_def_readable() form tun). Rx will be slowed down in this
> way. This patch avoids this by stop polling socket during rx
> processing. A small drawback is that this introduces some overheads in
> light load case because of the extra start/stop polling, but single
> netperf TCP_RR does not notice any change. In a super heavy load case,
> e.g using pktgen to inject packet to guest, we get about ~8.8%
> improvement on pps:
>
> before: ~1240000 pkt/s
> after: ~1350000 pkt/s
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

I guess this works though I suspect it's even faster to
maintain some state in the vq structure so we don't need
to play with waitq all the time.

For now

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

> ---
> drivers/vhost/net.c | 64 +++++++++++++++++++++++++++--------------------------
> 1 file changed, 33 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index f744eeb..1d3e45f 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -301,6 +301,32 @@ static bool vhost_can_busy_poll(struct vhost_dev *dev,
> !vhost_has_work(dev);
> }
>
> +static void vhost_net_disable_vq(struct vhost_net *n,
> + struct vhost_virtqueue *vq)
> +{
> + struct vhost_net_virtqueue *nvq =
> + container_of(vq, struct vhost_net_virtqueue, vq);
> + struct vhost_poll *poll = n->poll + (nvq - n->vqs);
> + if (!vq->private_data)
> + return;
> + vhost_poll_stop(poll);
> +}
> +
> +static int vhost_net_enable_vq(struct vhost_net *n,
> + struct vhost_virtqueue *vq)
> +{
> + struct vhost_net_virtqueue *nvq =
> + container_of(vq, struct vhost_net_virtqueue, vq);
> + struct vhost_poll *poll = n->poll + (nvq - n->vqs);
> + struct socket *sock;
> +
> + sock = vq->private_data;
> + if (!sock)
> + return 0;
> +
> + return vhost_poll_start(poll, sock->file);
> +}
> +
> static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
> struct vhost_virtqueue *vq,
> struct iovec iov[], unsigned int iov_size,
> @@ -613,6 +639,7 @@ static void handle_rx(struct vhost_net *net)
> if (!sock)
> goto out;
> vhost_disable_notify(&net->dev, vq);
> + vhost_net_disable_vq(net, vq);
>
> vhost_hlen = nvq->vhost_hlen;
> sock_hlen = nvq->sock_hlen;
> @@ -629,7 +656,7 @@ static void handle_rx(struct vhost_net *net)
> likely(mergeable) ? UIO_MAXIOV : 1);
> /* On error, stop handling until the next kick. */
> if (unlikely(headcount < 0))
> - break;
> + goto out;
> /* On overrun, truncate and discard */
> if (unlikely(headcount > UIO_MAXIOV)) {
> iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
> @@ -648,7 +675,7 @@ static void handle_rx(struct vhost_net *net)
> }
> /* Nothing new? Wait for eventfd to tell us
> * they refilled. */
> - break;
> + goto out;
> }
> /* We don't need to be notified again. */
> iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
> @@ -676,7 +703,7 @@ static void handle_rx(struct vhost_net *net)
> &fixup) != sizeof(hdr)) {
> vq_err(vq, "Unable to write vnet_hdr "
> "at addr %p\n", vq->iov->iov_base);
> - break;
> + goto out;
> }
> } else {
> /* Header came from socket; we'll need to patch
> @@ -692,7 +719,7 @@ static void handle_rx(struct vhost_net *net)
> &fixup) != sizeof num_buffers) {
> vq_err(vq, "Failed num_buffers write");
> vhost_discard_vq_desc(vq, headcount);
> - break;
> + goto out;
> }
> vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
> headcount);
> @@ -701,9 +728,10 @@ static void handle_rx(struct vhost_net *net)
> total_len += vhost_len;
> if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
> vhost_poll_queue(&vq->poll);
> - break;
> + goto out;
> }
> }
> + vhost_net_enable_vq(net, vq);
> out:
> mutex_unlock(&vq->mutex);
> }
> @@ -782,32 +810,6 @@ static int vhost_net_open(struct inode *inode, struct file *f)
> return 0;
> }
>
> -static void vhost_net_disable_vq(struct vhost_net *n,
> - struct vhost_virtqueue *vq)
> -{
> - struct vhost_net_virtqueue *nvq =
> - container_of(vq, struct vhost_net_virtqueue, vq);
> - struct vhost_poll *poll = n->poll + (nvq - n->vqs);
> - if (!vq->private_data)
> - return;
> - vhost_poll_stop(poll);
> -}
> -
> -static int vhost_net_enable_vq(struct vhost_net *n,
> - struct vhost_virtqueue *vq)
> -{
> - struct vhost_net_virtqueue *nvq =
> - container_of(vq, struct vhost_net_virtqueue, vq);
> - struct vhost_poll *poll = n->poll + (nvq - n->vqs);
> - struct socket *sock;
> -
> - sock = vq->private_data;
> - if (!sock)
> - return 0;
> -
> - return vhost_poll_start(poll, sock->file);
> -}
> -
> static struct socket *vhost_net_stop_vq(struct vhost_net *n,
> struct vhost_virtqueue *vq)
> {
> --
> 1.8.3.1