[PATCH V2 2/2] vhost_net: conditionally enable tx polling

From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Jason Wang <jasowang@redhat.com>
Subject: [PATCH V2 2/2] vhost_net: conditionally enable tx polling
Date: Mon, 30 May 2016 02:47:54 -0400	[thread overview]
Message-ID: <1464590874-39539-3-git-send-email-jasowang@redhat.com> (raw)
In-Reply-To: <1464590874-39539-1-git-send-email-jasowang@redhat.com>

We always poll tx for socket, this is sub optimal since:

- it will be only used when we exceed the sndbuf of the socket.
- since we use two independent polls for tx and vq, this will slightly
  increase the waitqueue traversing time and more important, vhost
  could not benefit from commit
  9e641bdcfa4ef4d6e2fbaa59c1be0ad5d1551fd5 ("net-tun: restructure
  tun_do_read for better sleep/wakeup efficiency") even if we've
  stopped rx polling during handle_rx since tx poll were still left in
  the waitqueue.

Fix this by conditionally enable tx polling only when -EAGAIN were
met.

Test shows about 8% improvement on guest rx pps.

Before: ~1350000
After:  ~1460000

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/net.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index e91603b..5a05fa0 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -378,6 +378,7 @@ static void handle_tx(struct vhost_net *net)
 		goto out;
 
 	vhost_disable_notify(&net->dev, vq);
+	vhost_net_disable_vq(net, vq);
 
 	hdr_size = nvq->vhost_hlen;
 	zcopy = nvq->ubufs;
@@ -459,6 +460,8 @@ static void handle_tx(struct vhost_net *net)
 					% UIO_MAXIOV;
 			}
 			vhost_discard_vq_desc(vq, 1);
+			if (err == -EAGAIN)
+				vhost_net_enable_vq(net, vq);
 			break;
 		}
 		if (err != len)
-- 
1.8.3.1
