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Date:   Wed, 4 Jul 2018 11:27:05 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        "David S. Miller" <davem@...emloft.net>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Tonghao Zhang <xiangxia.m.yue@...il.com>
Subject: Re: [PATCH v2 net-next 4/4] vhost_net: Avoid rx vring kicks during
 busyloop



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.
>
> Signed-off-by: Toshiaki Makita <makita.toshiaki@....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)
>   
>   	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 */

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

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