linux-kernel - Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

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Message-ID: <20170329150538-mutt-send-email-mst@kernel.org>
Date:   Wed, 29 Mar 2017 15:07:10 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb
 array during busy polling

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
> For the socket that exports its skb array, we can use lockless polling
> to avoid touching spinlock during busy polling.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/vhost/net.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 53f09f2..41153a3 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
>  	return len;
>  }
>  
> -static int sk_has_rx_data(struct sock *sk)
> +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
>  {
>  	struct socket *sock = sk->sk_socket;
>  
> +	if (rvq->rx_array)
> +		return !__skb_array_empty(rvq->rx_array);
> +
>  	if (sock->ops->peek_len)
>  		return sock->ops->peek_len(sock);
>  

I don't see which patch adds __skb_array_empty.

> @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
>  		endtime = busy_clock() + vq->busyloop_timeout;
>  
>  		while (vhost_can_busy_poll(&net->dev, endtime) &&
> -		       !sk_has_rx_data(sk) &&
> +		       !sk_has_rx_data(rvq, sk) &&
>  		       vhost_vq_avail_empty(&net->dev, vq))
>  			cpu_relax();
>  
> -- 
> 2.7.4