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Date: Tue, 3 Apr 2018 08:08:26 +0000
From: haibinzhang(张海斌) <haibinzhang@...cent.com>
To: "mst@...hat.com" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: lidongchen(陈立东) <lidongchen@...cent.com>,
yunfangtai(台运方) <yunfangtai@...cent.com>
Subject: [PATCH] vhost-net: add limitation of sent packets for tx polling
handle_tx will delay rx for a long time when tx busy polling udp packets
with small length(e.g. 1byte udp payload), because setting VHOST_NET_WEIGHT
takes into account only sent-bytes but no single packet length.
Tests were done between two Virtual Machines using netperf(UDP_STREAM, len=1),
then another machine pinged the client. Result shows as follow:
Packet# Ping-Latency(ms)
min avg max
Origin 3.319 18.489 57.503
64 1.643 2.021 2.552
128 1.825 2.600 3.224
256 1.997 2.710 4.295
512* 1.860 3.171 4.631
1024 2.002 4.173 9.056
2048 2.257 5.650 9.688
4096 2.093 8.508 15.943
512 is selected, which is multi-VRING_SIZE and close to VHOST_NET_WEIGHT/MTU.
To evaluate this change, another tests were done using netperf(RR, TX) between
two machines with Intel(R) Xeon(R) Gold 6133 CPU @ 2.50GHz. Result as follow
does not show obvious changes:
TCP_RR
size/sessions/+thu%/+normalize%
1/ 1/ -7%/ -2%
1/ 4/ +1%/ 0%
1/ 8/ +1%/ -2%
64/ 1/ -6%/ 0%
64/ 4/ 0%/ +2%
64/ 8/ 0%/ 0%
256/ 1/ -3%/ -4%
256/ 4/ +3%/ +4%
256/ 8/ +2%/ 0%
UDP_RR
size/sessions/+thu%/+normalize%
1/ 1/ -5%/ +1%
1/ 4/ +4%/ +1%
1/ 8/ -1%/ -1%
64/ 1/ -2%/ -3%
64/ 4/ -5%/ -1%
64/ 8/ 0%/ -1%
256/ 1/ +7%/ +1%
256/ 4/ +1%/ +1%
256/ 8/ +2%/ +2%
TCP_STREAM
size/sessions/+thu%/+normalize%
64/ 1/ 0%/ -3%
64/ 4/ +3%/ -1%
64/ 8/ +9%/ -4%
256/ 1/ +1%/ -4%
256/ 4/ -1%/ -1%
256/ 8/ +7%/ +5%
512/ 1/ +1%/ 0%
512/ 4/ +1%/ -1%
512/ 8/ +7%/ -5%
1024/ 1/ 0%/ -1%
1024/ 4/ +3%/ 0%
1024/ 8/ +8%/ +5%
2048/ 1/ +2%/ +2%
2048/ 4/ +1%/ 0%
2048/ 8/ -2%/ 0%
4096/ 1/ -2%/ 0%
4096/ 4/ +2%/ 0%
4096/ 8/ +9%/ -2%
Signed-off-by: Haibin Zhang <haibinzhang@...cent.com>
Signed-off-by: Yunfang Tai <yunfangtai@...cent.com>
Signed-off-by: Lidong Chen <lidongchen@...cent.com>
---
drivers/vhost/net.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 8139bc70ad7d..13a23f3f3ea4 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -44,6 +44,10 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
* Using this limit prevents one virtqueue from starving others. */
#define VHOST_NET_WEIGHT 0x80000
+/* Max number of packets transferred before requeueing the job.
+ * Using this limit prevents one virtqueue from starving rx. */
+#define VHOST_NET_PKT_WEIGHT 512
+
/* MAX number of TX used buffers for outstanding zerocopy */
#define VHOST_MAX_PEND 128
#define VHOST_GOODCOPY_LEN 256
@@ -473,6 +477,7 @@ static void handle_tx(struct vhost_net *net)
struct socket *sock;
struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
bool zcopy, zcopy_used;
+ int sent_pkts = 0;
mutex_lock(&vq->mutex);
sock = vq->private_data;
@@ -580,7 +585,8 @@ static void handle_tx(struct vhost_net *net)
else
vhost_zerocopy_signal_used(net, vq);
vhost_net_tx_packet(net);
- if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
+ if (unlikely(total_len >= VHOST_NET_WEIGHT) ||
+ unlikely(++sent_pkts >= VHOST_NET_PKT_WEIGHT)) {
vhost_poll_queue(&vq->poll);
break;
}
--
2.12.3
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