commit a2ac99905f1ea8b15997a6ec39af69aa28a3653b upstream.
handle_tx will delay rx for tens or even hundreds of milliseconds 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.
Ping-Latencies shown below were tested between two Virtual Machines using netperf (UDP_STREAM, len=1), and then another machine pinged the client:
vq size=256 Packet-Weight Ping-Latencies(millisecond) min avg max Origin 3.319 18.489 57.303 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
vq size=512 Packet-Weight Ping-Latencies(millisecond) min avg max Origin 6.537 29.177 66.245 64 2.798 3.614 4.403 128 2.861 3.820 4.775 256 3.008 4.018 4.807 512 3.254 4.523 5.824 1024 3.079 5.335 7.747 2048 3.944 8.201 12.762 4096 4.158 11.057 19.985
Seems pretty consistent, a small dip at 2 VQ sizes. Ring size is a hint from device about a burst size it can tolerate. Based on benchmarks, set the weight to 2 * vq size.
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, and vq size was tweaked through qemu. Results shown below does not show obvious changes.
vq size=256 TCP_RR vq size=512 TCP_RR size/sessions/+thu%/+normalize% size/sessions/+thu%/+normalize% 1/ 1/ -7%/ -2% 1/ 1/ 0%/ -2% 1/ 4/ +1%/ 0% 1/ 4/ +1%/ 0% 1/ 8/ +1%/ -2% 1/ 8/ 0%/ +1% 64/ 1/ -6%/ 0% 64/ 1/ +7%/ +3% 64/ 4/ 0%/ +2% 64/ 4/ -1%/ +1% 64/ 8/ 0%/ 0% 64/ 8/ -1%/ -2% 256/ 1/ -3%/ -4% 256/ 1/ -4%/ -2% 256/ 4/ +3%/ +4% 256/ 4/ +1%/ +2% 256/ 8/ +2%/ 0% 256/ 8/ +1%/ -1%
vq size=256 UDP_RR vq size=512 UDP_RR size/sessions/+thu%/+normalize% size/sessions/+thu%/+normalize% 1/ 1/ -5%/ +1% 1/ 1/ -3%/ -2% 1/ 4/ +4%/ +1% 1/ 4/ -2%/ +2% 1/ 8/ -1%/ -1% 1/ 8/ -1%/ 0% 64/ 1/ -2%/ -3% 64/ 1/ +1%/ +1% 64/ 4/ -5%/ -1% 64/ 4/ +2%/ 0% 64/ 8/ 0%/ -1% 64/ 8/ -2%/ +1% 256/ 1/ +7%/ +1% 256/ 1/ -7%/ 0% 256/ 4/ +1%/ +1% 256/ 4/ -3%/ -4% 256/ 8/ +2%/ +2% 256/ 8/ +1%/ +1%
vq size=256 TCP_STREAM vq size=512 TCP_STREAM size/sessions/+thu%/+normalize% size/sessions/+thu%/+normalize% 64/ 1/ 0%/ -3% 64/ 1/ 0%/ 0% 64/ 4/ +3%/ -1% 64/ 4/ -2%/ +4% 64/ 8/ +9%/ -4% 64/ 8/ -1%/ +2% 256/ 1/ +1%/ -4% 256/ 1/ +1%/ +1% 256/ 4/ -1%/ -1% 256/ 4/ -3%/ 0% 256/ 8/ +7%/ +5% 256/ 8/ -3%/ 0% 512/ 1/ +1%/ 0% 512/ 1/ -1%/ -1% 512/ 4/ +1%/ -1% 512/ 4/ 0%/ 0% 512/ 8/ +7%/ -5% 512/ 8/ +6%/ -1% 1024/ 1/ 0%/ -1% 1024/ 1/ 0%/ +1% 1024/ 4/ +3%/ 0% 1024/ 4/ +1%/ 0% 1024/ 8/ +8%/ +5% 1024/ 8/ -1%/ 0% 2048/ 1/ +2%/ +2% 2048/ 1/ -1%/ 0% 2048/ 4/ +1%/ 0% 2048/ 4/ 0%/ -1% 2048/ 8/ -2%/ 0% 2048/ 8/ 5%/ -1% 4096/ 1/ -2%/ 0% 4096/ 1/ -2%/ 0% 4096/ 4/ +2%/ 0% 4096/ 4/ 0%/ 0% 4096/ 8/ +9%/ -2% 4096/ 8/ -5%/ -1%
Acked-by: Michael S. Tsirkin mst@redhat.com Signed-off-by: Haibin Zhang haibinzhang@tencent.com Signed-off-by: Yunfang Tai yunfangtai@tencent.com Signed-off-by: Lidong Chen lidongchen@tencent.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Ben Hutchings ben.hutchings@codethink.co.uk Signed-off-by: Sasha Levin sashal@kernel.org --- 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 f463171352245..b8496f713bc62 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -39,6 +39,10 @@ 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(vq) ((vq)->num * 2) + /* MAX number of TX used buffers for outstanding zerocopy */ #define VHOST_MAX_PEND 128 #define VHOST_GOODCOPY_LEN 256 @@ -308,6 +312,7 @@ 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; @@ -408,7 +413,8 @@ static void handle_tx(struct vhost_net *net) vhost_zerocopy_signal_used(net, vq); total_len += len; 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(vq))) { vhost_poll_queue(&vq->poll); break; }