Linux tc htb bandwidth ceil being ignored and giving improper results

htblinuxtctraffictraffic-shaping

I'm setting up some htb packet queues like so:

tc qdisc add dev eth0 root handle 10: htb
tc qdisc add dev eth1 root handle 10: htb

tc class add dev eth0 parent 10: classid 10:1012 htb rate 750kbps ceil 750kbps
tc filter add dev eth0 parent 10: protocol ip prio 10 handle 1: cgroup
tc class add dev eth1 parent 10: classid 10:1012 htb rate 750kbps ceil 750kbps
tc filter add dev eth1 parent 10: protocol ip prio 10 handle 1: cgroup

And am testing it by downloading a 10MB file using wget.
I have verified that the packets have the correct classid on them.

When I do the download without these tc rules, I get an average download speed of ~ 9MB/s

When I apply the limit, my speed drops, but it drops to the wrong number. It tops off consistently at 3.7MB/s.

I have no idea why my limit is going over by so much especially considering I have a ceil set. I did notice that the download appears to start limited at 750kbps, but then starts incrementily gaining speed.

Any one have any ideas what I'm doing wrong?

Cheers!

Best Answer

Without further knowledge on your actual config I am going to assume you have a cgroup problem.

Try this to exclude your cgroups and just to limit the device itself.

#!/bin/bash

# Using ifb device to shape ingress traffic
modprobe ifb
ifconfig ifb0 up

# flush tc
tc qdisc del dev eth0 root &> /dev/null
tc qdisc del dev eth0 ingress &> /dev/null
tc qdisc del dev ifb0 root &> /dev/null

# limit all outbound traffic
tc qdisc add dev eth0 root handle 1: htb default 1
tc class add dev eth0 parent 1: classid 1:1 htb rate 1mbit

# forward inbound traffic to ifb
tc qdisc add dev eth0 ingress
tc filter add dev eth0 parent ffff: protocol all u32 match u32 0 0 action mirred egress redirect dev ifb0

# limit all inbound traffic via ifb egress
tc qdisc add dev ifb0 root handle 1: htb default 1
tc class add dev ifb0 parent 1: classid 1:1 htb rate 1mbit

Test and you should see that it works both inbound and outbound. If you only want to limit in one direction, just ignore the other part.

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