netdev - [PATCH net-next v8 7/7] net: vhost: make busyloop

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Date:   Sun, 19 Aug 2018 05:11:26 -0700
From:   xiangxia.m.yue@...il.com
To:     jasowang@...hat.com, mst@...hat.com, makita.toshiaki@....ntt.co.jp
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Tonghao Zhang <xiangxia.m.yue@...il.com>
Subject: [PATCH net-next v8 7/7] net: vhost: make busyloop_intr more accurate

From: Tonghao Zhang <xiangxia.m.yue@...il.com>

The patch uses vhost_has_work_pending() to check if
the specified handler is scheduled, because in the most case,
vhost_has_work() return true when other side handler is added
to worker list. Use the vhost_has_work_pending() insead of
vhost_has_work().

Topology:
[Host] ->linux bridge -> tap vhost-net ->[Guest]

TCP_STREAM (netperf):
* Without the patch:  38035.39 Mbps, 3.37 us mean latency
* With the patch:     38409.44 Mbps, 3.34 us mean latency

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
---
 drivers/vhost/net.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index db63ae2..b6939ef 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -487,10 +487,8 @@ static void vhost_net_busy_poll(struct vhost_net *net,
 	endtime = busy_clock() + busyloop_timeout;
 
 	while (vhost_can_busy_poll(endtime)) {
-		if (vhost_has_work(&net->dev)) {
-			*busyloop_intr = true;
+		if (vhost_has_work(&net->dev))
 			break;
-		}
 
 		if ((sock_has_rx_data(sock) &&
 		     !vhost_vq_avail_empty(&net->dev, rvq)) ||
@@ -513,6 +511,11 @@ static void vhost_net_busy_poll(struct vhost_net *net,
 	    !vhost_has_work_pending(&net->dev, VHOST_NET_VQ_RX))
 		vhost_net_enable_vq(net, rvq);
 
+	if (vhost_has_work_pending(&net->dev,
+				   poll_rx ?
+				   VHOST_NET_VQ_RX: VHOST_NET_VQ_TX))
+		*busyloop_intr = true;
+
 	mutex_unlock(&vq->mutex);
 }
 
-- 
1.8.3.1