HFSC problem

Linux Advanced Routing and Traffic Control

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Hi to all,

I want to use HFSC scheduling at output interfaces of software routers
in my testbed. I used HTB before, but since that is not good solution
for delay sensitive applications I decided to try HFSC. For the
beginning, I connected two host to one PC router:

H1(8.8.8.12)----Router-----H2(8.8.8.11)

However with HFSC I got much worse results then with HTB. I cannot
figure out what I did wrong. My experiment was really simple. From H1
I generated one UDP flow with rate 100kbit/s to H2.  On output
interface of the router (towards H2) I configured policy in the
following way:

tc qdisc add dev eth0 root handle 1: hfsc default 11
tc class add dev eth0 parent 1: classid 1:1 hfsc ls rate 100000kbit ul
rate 100000kbit
tc class add dev eth0 parent 1:1 classid 1:11 hfsc rt m1 400kbit d
30ms m2  100kbit
tc class add dev eth0 parent 1:1 classid 1:10 hfsc ls rate 10000kbit
ul rate 10000kbit

and defined tc filter:

tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 match ip src
8.8.8.12 flowid 1:11

I synchronized hosts' clock and run tcpdump on both to measure delay.
Results were disappointing because some of the packets experienced
delay of almost 200ms instead od 30ms. I have never had such large
delay with HTB. The longest delay I had with HTB was about 150 ms.

Can you please help me to solve this problem? I do not see any other
Linux scheduling alternative that can guarantee delay...

Regards,

S.
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