[LARTC] HTB not that exact

[Stefan Rompf <srompf@isg.de>]

Hi,

I'm experimenting using the HTB queueing discipline for traffic shaping.
However, it is not really exact. Currently, I try this setup:

tc qdisc add dev eth0 root handle 1: htb default 3

tc class add dev eth0 parent 1: classid 1:1 htb rate 20Mbit burst 4kB
tc qdisc add dev eth0 parent 1:1 sfq

tc class add dev eth0 parent 1: classid 1:2 htb rate 3Mbit burst 2kB
tc qdisc add dev eth0 parent 1:2 sfq

tc class add dev eth0 parent 1: classid 1:3 htb rate 77Mbit burst 150kB
tc qdisc add dev eth0 parent 1:3 sfq

tc filter add dev eth0 parent 1:0 prio 7 protocol ip handle 1 fw classid
1:1
tc filter add dev eth0 parent 1:0 prio 7 protocol ip handle 2 fw classid
1:2

/usr/local/sbin/iptables -t mangle -F OUTPUT
/usr/local/sbin/iptables -t mangle -A OUTPUT -p tcp --dport 9021 -j MARK
--set-mark 1
/usr/local/sbin/iptables -t mangle -A OUTPUT -p tcp --dport 9022:9023 -j
MARK --set-mark 2

The network adaptor is connected to a 100MBit switch. When testing with
netio, I can send up to 370kB/sec through class 1:2 and up to 2,4MB/sec
via class 1:1, both measured by one/multiple instances of netio and the
rate output of "tc -s class dev eth0". This effect occurs with Linux
2.4.16,  kernel either compiled with HZ set to 100 or 1024, and of
course independant of the filter type used. During the tests, no packets
need to be dropped, htb just delays.

Output when two netio instances are sending to class 1:2 for some time:

root@barkeeper /root/ >tc -s class list dev eth0
[...]

class htb 1:2 root leaf 800e: prio 0 rate 3Mbit ceil 3Mbit burst 2Kb
cburst 2Kb
 Sent 236734498 bytes 156441 pkts (dropped 0, overlimits 301823)
 rate 378286bps 250pps backlog 44p
 lended: 156397 borrowed: 0 giants: 0 injects: 0
 tokens: -3714 ctokens: -3714

[...]


tbf seems not to be able to do exact rate limiting, too. Anything wrong
in my configuration, or am I just taking false statistics?

Stefan

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