Re: [PATCH v2 net-next 3/4] vhost_net: Avoid rx queue wake-ups during busypoll

Jason Wang
2018-07-04T03:26:35Z

On 2018年07月03日 15:31, Toshiaki Makita wrote:
> We may run handle_rx() while rx work is queued. For example a packet can
> push the rx work during the window before handle_rx calls
> vhost_net_disable_vq().
> In that case busypoll immediately exits due to vhost_has_work()
> condition and enables vq again. This can lead to another unnecessary rx
> wake-ups, so poll rx work instead of enabling the vq.
>
> Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
> ---
> drivers/vhost/net.c | 26 +++++++++++++++++++-------
> 1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 811c0e5..791bc8b 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -653,7 +653,8 @@ static void vhost_rx_signal_used(struct vhost_net_virtqueue *nvq)
> nvq->done_idx = 0;
> }
>
> -static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
> +static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
> + bool *busyloop_intr)
> {
> struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
> struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
> @@ -671,11 +672,16 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
> preempt_disable();
> endtime = busy_clock() + tvq->busyloop_timeout;
>
> - while (vhost_can_busy_poll(endtime) &&
> - !vhost_has_work(&net->dev) &&
> - !sk_has_rx_data(sk) &&
> - vhost_vq_avail_empty(&net->dev, tvq))
> + while (vhost_can_busy_poll(endtime)) {
> + if (vhost_has_work(&net->dev)) {
> + *busyloop_intr = true;
> + break;
> + }
> + if (sk_has_rx_data(sk) ||
> + !vhost_vq_avail_empty(&net->dev, tvq))
> + break;
> cpu_relax();
> + }
>
> preempt_enable();
>
> @@ -795,6 +801,7 @@ static void handle_rx(struct vhost_net *net)
> s16 headcount;
> size_t vhost_hlen, sock_hlen;
> size_t vhost_len, sock_len;
> + bool busyloop_intr = false;
> struct socket *sock;
> struct iov_iter fixup;
> __virtio16 num_buffers;
> @@ -818,7 +825,9 @@ static void handle_rx(struct vhost_net *net)
> vq->log : NULL;
> mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
>
> - while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk))) {
> + 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,
> @@ -905,7 +914,10 @@ static void handle_rx(struct vhost_net *net)
> goto out;
> }
> }
> - vhost_net_enable_vq(net, vq);
> + if (unlikely(busyloop_intr))
> + vhost_poll_queue(&vq->poll);
> + else
> + vhost_net_enable_vq(net, vq);
> out:
> vhost_rx_signal_used(nvq);
> mutex_unlock(&vq->mutex);

Acked-by: Jason Wang <jasowang@redhat.com>

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