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There is tc queue discipline DRR(Dificite Round Robin) .

It has same capabilities, as HTB, but instead of using buckets, filled with tokens, it just assignes every queue some Dificit Counter. On packet sending DC is decreased by packet size. If DC is less than packet size, DC is increased by queue's quantum and next queue is processed. So, it can divide outgoing traffec in some ratio, without knowing channel width(which is required for HTB). See http://www.unix.com/man-page/linux/8/tc-drr/

Setup: two hosts, 172.16.1.1 и 172.16.1.2.

On first host we are listening to traffic:

nc -l 8111
nc -l 8112

On second host we check speed:

pv /dev/zero | nc 172.16.1.1 8111
pv /dev/zero | nc 172.16.1.1 8112

Now speed is equal(pv is utility allowing to measure speed of data tranfering via pipeline). Add DRR on second host(HTB at top is used to emulate real channel speed limits):

tc qdisc add dev eth0 root handle 1: htb
tc class add dev eth0 parent 1: classid 1:1 htb rate 100mbit ceil 100mbit
tc qdisc add dev eth0 parent 1:1 handle 2: drr
tc class add dev eth0 parent 2: classid 2:1 drr quantum 600
tc class add dev eth0 parent 2: classid 2:2 drr quantum 1400
tc filter add dev eth0 parent 1: protocol ip prio 1 u32 match ip dport 8111 0xffff classid 2:1
tc filter add dev eth0 parent 1: protocol ip prio 1 u32 match ip dport 8112 0xffff classid 2:2

Speed remains equal :( What am I doing wrong?

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  • Obvious question but is the client on a different host to the server?
    – Matthew Ife
    Sep 17, 2013 at 18:17
  • Yes, it's 2 virtual machines
    – Selivanov Pavel
    Sep 17, 2013 at 21:03
  • Is the speed equal at ~50mbits? Or is it not hitting the htb contraints?
    – Jehan
    Jan 4, 2017 at 19:03

2 Answers 2

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Answer: DRR does not drop packets itself. To get the desired behavior, add child qdiscs to the DRR child classes like pfifo limit 50 to cause the child qdisc to drop packets instead of queueing them effectively indefinitely. The solution was found here: linux.org.ru thread

Reference: man tc-drr

NOTES This implementation does not drop packets from the longest queue on overrun, as limits are handled by the individual child qdiscs.

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+75

drr is a scheduler, you still have to allocate different bandwidth to classes with htb. I guess you though specifying quantum as 600 and 1400 will give close to 1:2 ratio. In fact it will not. You may get close to that ratio on your config only in case of congestion, e.g. create multiple UDP streams, and then measure two in question, but it's still not the thing you are expecting.

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  • Why? If I understand algorithm correctly, in case of congestion(new packets appear faster than they can be sent out) for 2 classes with quamtums 600 and 1400 DRR will send packets from second class more often: for example, if all packets have size 1500(default Ethernet MTU) for every 6 packets in first class 14 packets of second class will be sent. Where is my mistake?
    – Selivanov Pavel
    Sep 17, 2013 at 16:26
  • Did you try at least three UDP streams? It's important to have UDP streams in order to create congestion, third stream should not match either filter. No congestion -> no QoS kicks in at all. If no explicit bandwidth specified, quantum should play role, but again only if congestion happens. Whole idea behind qos that it kicks in only if congestion in particular class in hierarchy happens.
    – Alex_www
    Sep 18, 2013 at 1:26

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