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

[Jason Wang]

On 2017年03月29日 20:07, Michael S. Tsirkin wrote:
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 <jasow...@redhat.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.

This is not something new, it was introduced by ad69f35d1dc0a 
("skb_array: array based FIFO for skbs").

Thanks


@@ -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