On 2017年12月01日 22:37, Michael S. Tsirkin wrote:
On Fri, Dec 01, 2017 at 03:11:05PM +0800, Jason Wang wrote:
On 2017年12月01日 13:54, 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>
---
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;
I suggest to reorder this patch to 3/3.
Thanks
Why? This doesn't cause any new leaks, does it?
It doesn't, just think it can ease the downstream back porting in case
patch 2-3 were missed if somebody did a bisect and just backport patch 1.
Thanks
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
