On Tue, Nov 28, 2017 at 07:50:58PM +0200, Michael S. Tsirkin wrote: > 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> > > Looks like a good way to fix it, but it will still leak if recvmsg > returns a wrong length (I'm not sure this can happen in practice, but > best to keep it simple). Right, it is better to defend this case, will include it in v2. > > Also, we need to add this before each recvmsg, including overrun, > and discard on error. OK. Wei > > > --- > > 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
