On 2017年11月29日 01:17, 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> --- 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)) {
You need do msg.msg_control = vhost_net_buf_consume() here too, otherwise we may still get it leaked.
Thanks
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:
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