On Tue, Nov 28, 2017 at 12:17:16PM -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 deferring it a moment later > in this patch. > > Signed-off-by: Wei Xu <wexu@xxxxxxxxxx> Given the amount of effort Matthew has put into this, you definitely want Reported-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxxxxxxx> here. Let's give credit where credit is due. Thanks a lot Matthew! > --- > drivers/vhost/net.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 8d626d7..e76535e 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -778,8 +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); > @@ -809,6 +807,8 @@ static void handle_rx(struct vhost_net *net) > */ > iov_iter_advance(&msg.msg_iter, vhost_hlen); > } > + if (nvq->rx_array) > + msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > err = sock->ops->recvmsg(sock, &msg, > sock_len, MSG_DONTWAIT | MSG_TRUNC); > /* Userspace might have consumed the packet meanwhile: > -- > 1.8.3.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
