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

From: Jason Wang
Date: Mon May 30 2016 - 02:48:33 EST

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

Test shows about 8% improvement on guest rx pps.

Before: ~1350000
After: ~1460000

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
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)
vhost_discard_vq_desc(vq, 1);
+ if (err == -EAGAIN)
+ vhost_net_enable_vq(net, vq);
if (err != len)