Re: [PATCH v2 net-next 4/4] vhost_net: Avoid rx vring kicks during busyloop

Jason Wang
2018-07-03T09:05:22Z

On 2018年07月03日 15:31, Toshiaki Makita wrote:
> We may run out of avail rx ring descriptor under heavy load but busypoll
> did not detect it so busypoll may have exited prematurely. Avoid this by
> checking rx ring full during busypoll.

Actually, we're checking whether it was empty in fact?

>
> Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
> ---
> drivers/vhost/net.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 791bc8b..b224036 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -658,6 +658,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> {
> struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
> struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
> + struct vhost_virtqueue *rvq = &rnvq->vq;
> struct vhost_virtqueue *tvq = &tnvq->vq;
> unsigned long uninitialized_var(endtime);
> int len = peek_head_len(rnvq, sk);
> @@ -677,7 +678,8 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> *busyloop_intr = true;
> break;
> }
> - if (sk_has_rx_data(sk) ||
> + if ((sk_has_rx_data(sk) &&
> + !vhost_vq_avail_empty(&net->dev, rvq)) ||
> !vhost_vq_avail_empty(&net->dev, tvq))
> break;
> cpu_relax();
> @@ -827,7 +829,6 @@ static void handle_rx(struct vhost_net *net)
>

I thought below codes should belong to patch 3. Or I may miss something.

Thanks

> while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
> &busyloop_intr))) {
> - busyloop_intr = false;
> sock_len += sock_hlen;
> vhost_len = sock_len + vhost_hlen;
> headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
> @@ -838,7 +839,9 @@ static void handle_rx(struct vhost_net *net)
> goto out;
> /* OK, now we need to know about added descriptors. */
> if (!headcount) {
> - if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> + if (unlikely(busyloop_intr)) {
> + vhost_poll_queue(&vq->poll);
> + } else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> /* They have slipped one in as we were
> * doing that: check again. */
> vhost_disable_notify(&net->dev, vq);
> @@ -848,6 +851,7 @@ static void handle_rx(struct vhost_net *net)
> * they refilled. */
> goto out;
> }
> + busyloop_intr = false;
> if (nvq->rx_ring)
> msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
> /* On overrun, truncate and discard */

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