[ovs-discuss] QoS Egress Port Traffic Shaping (linux-hfsc ) not Working as Expected for UDP Traffic

[Ramzah Rehman]

 I have two servers connected via 1Gbps cable. I have installed OVS 2.8 on
server one. I have a switch named OVS_BR_LEAF_1 on it. I experimented with
QoS traffic shaping. I have connected eth3 of server one to ovs-switch on
port 2. I want traffic going from server one to server two to observer QoS
traffic rate that I specify.

I added following configuration:

#ovs-vsctl -- set port eth3 qos=@newqos -- --id=@newqos create qos
type=linux-hfsc other-config:max-rate=1000000000 queues:1=@q1 -- --id=@q1
create queue other-config:min-rate=x other-config:max-rate=x

I have following flow entries in my switch:
#vs-ofctl add-flow OVS_BR_LEAF_1
priority=6000,in_port=LOCAL,actions=set_queue:1,normal
#ovs-ofctl add-flow OVS_BR_LEAF_1 priority=6000,in_port=2,actions=normal

Then I checked throughput for TCP traffic (from server one to two) via
iperf and got following results:

got 846 Mbps for x=900 Mbps
got 757 Mbps for x=800 Mbps
got 653 Mbps for x=700 Mbps
got 428 Mbps for x=450 Mbps
got 381 Mbps for x=400 Mbps
got 287 Mbps for x=300 Mbps
got 239 Mbps for x=250 Mbps
got 192 Mbps for x=200 Mbps

Seems like traffic shaping is working fine for TCP traffic. However, for
UDP, I got these results:

148 Mbps for x=800 Mbps
185 Mbps for x=300 Mbps
131 Mbps for x=200 Mbps
93 Mbps for x=100 Mbps
77 Mbps for x=80 Mbps
28.9 Mbps for x=30 Mbps
19.3 Mbps for x=20 Mbps

For UDP, traffic shaping works fine till x=100Mpbs, but for higher values
is shows unexpected behavior. Is there an explanation?

Please help.

Best Regards,
Ramzah Rehman
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