On Fri, Dec 01, 2017 at 05:10:36AM -0500, wexu@xxxxxxxxxx wrote: > From: Wei Xu <wexu@xxxxxxxxxx> > > Matthew found a roughly 40% tcp throughput regression with commit > c67df11f(vhost_net: try batch dequing from skb array) as discussed > in the following thread: > https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg187936.html > > Eventually we figured out that it was a skb leak in handle_rx() > when sending packets to the VM. This usually happens when a guest > can not drain out vq as fast as vhost fills in, afterwards it sets > off the traffic jam and leaks skb(s) which occurs as no headcount > to send on the vq from vhost side. > > This can be avoided by making sure we have got enough headcount > before actually consuming a skb from the batched rx array while > transmitting, which is simply done by moving checking the zero > headcount a bit ahead. > > Signed-off-by: Wei Xu <wexu@xxxxxxxxxx> > Reported-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxxxxxxx> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > --- > drivers/vhost/net.c | 20 ++++++++++---------- > 1 file changed, 10 insertions(+), 10 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 8d626d7..c7bdeb6 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -778,16 +778,6 @@ static void handle_rx(struct vhost_net *net) > /* On error, stop handling until the next kick. */ > if (unlikely(headcount < 0)) > goto out; > - if (nvq->rx_array) > - msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > - /* On overrun, truncate and discard */ > - if (unlikely(headcount > UIO_MAXIOV)) { > - iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); > - err = sock->ops->recvmsg(sock, &msg, > - 1, MSG_DONTWAIT | MSG_TRUNC); > - pr_debug("Discarded rx packet: len %zd\n", sock_len); > - continue; > - } > /* OK, now we need to know about added descriptors. */ > if (!headcount) { > if (unlikely(vhost_enable_notify(&net->dev, vq))) { > @@ -800,6 +790,16 @@ static void handle_rx(struct vhost_net *net) > * they refilled. */ > goto out; > } > + if (nvq->rx_array) > + msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > + /* On overrun, truncate and discard */ > + if (unlikely(headcount > UIO_MAXIOV)) { > + iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); > + err = sock->ops->recvmsg(sock, &msg, > + 1, MSG_DONTWAIT | MSG_TRUNC); > + pr_debug("Discarded rx packet: len %zd\n", sock_len); > + continue; > + } > /* We don't need to be notified again. */ > iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len); > fixup = msg.msg_iter; > -- > 1.8.3.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
