Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling
From: Jason Wang
Date: Wed Mar 29 2017 - 23:53:33 EST
On 2017å03æ30æ 10:33, Michael S. Tsirkin wrote:
On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote:
On 2017å03æ29æ 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 <jasowang@xxxxxxxxxx>
---
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
Same comment about a compiler barrier applies then.
Ok, rethink about this, since skb_array could be resized, using lockless
version seems wrong.
For the comment of using compiler barrier, caller
(vhost_net_rx_peek_head_len) uses cpu_relax(). But I haven't figured out
why a compiler barrier is needed here. Could you please explain?
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