[PATCH] vhost: make vhost_zerocopy_callback more efficient by poll_queue base on vhost status

[Qin Chuanyu <qinchuanyu@huawei.com>]

guest kick vhost base on vring flag status and get perfermance improved,
vhost_zerocopy_callback could do this in the same way, as
virtqueue_enable_cb need one more check after change the status of
avail_ring flags, vhost also do the same thing after vhost_enable_notify

test result list as below:
guest and host: suse11sp3, netperf, intel 2.4GHz
+-------+----------+---------+----------+---------+
|       |   old              |   new              |
+-------+----------+---------+----------+---------+
|  UDP  |  Gbit/s  |   PPS   |  Gbit/s  |   PPS   |
|  256  | 0.74805  | 321309  | 0.77933  | 334743  |
|  512  |   1.42   | 328475  |   1.44   | 333550  |
| 1024  |   2.79   | 334426  |   2.81   | 336986  |
| 1460  |   3.71   | 316215  |   4.02   | 342325  |
+-------+----------+---------+----------+---------+

Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com>
---
  drivers/vhost/net.c |   10 +++++++++-
  1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index a0fa5de..9bc0a15 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -322,7 +322,9 @@ static void vhost_zerocopy_callback(struct ubuf_info 
*ubuf, bool success)
  	 * (the value 16 here is more or less arbitrary, it's tuned to trigger
  	 * less than 10% of times).
  	 */
-	if (cnt <= 1 || !(cnt % 16))
+	smp_rmb();
+	if ((!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
+			&& (cnt <= 1 || !(cnt % 16)))
  		vhost_poll_queue(&vq->poll);

  	rcu_read_unlock_bh();
@@ -386,6 +388,12 @@ static void handle_tx(struct vhost_net *net)
  				vhost_disable_notify(&net->dev, vq);
  				continue;
  			}
+			/* there might skb been freed between last
+			* vhost_zerocopy_signal_used and vhost_enable_notify,
+			* so one more check is needed.
+			*/
+			if (zcopy)
+				vhost_zerocopy_signal_used(net, vq);
  			break;
  		}
  		if (in) {
-- 
1.7.3.1.msysgit.0