tc burst size rollover

tc burst size rollover

[Brian Rak]

I'm seeing some weird behavior when I'm trying to add some htb queue 
settings with large burst sizes.  It seems that if I specify a burst 
size over 3355443kb, the number rolls over.  For example:

# tc class add dev vnet1 parent 1: classid 1:1 htb rate 12500kbps ceil 
125000kbps burst 3355444kb
# tc class show dev vnet1  parent 1:
class htb 1:1 root prio 0 rate 100000Kbit ceil 1000Mbit burst 812b 
cburst 1375b

Is there supposed to be a limitation here? I can't seem to find anything 
in the documentation talking about it.

I've tested this with iproute2-3.12.0 on 3.13.1-1.el6.elrepo.x86_64. 
This is the full set of commands I was using (these are what libvirt 
applies by default):

tc qdisc del dev vnet1 root
tc qdisc del dev vnet1 ingress
tc qdisc add dev vnet1 root handle 1: htb default 1
tc class add dev vnet1 parent 1: classid 1:1 htb rate 12500kbps ceil 
125000kbps burst 3355444kb
tc class show dev vnet1  parent 1:


Ultimately, I'm trying to allow bursts at 1000mbit up to 100GB or so, 
then restrict things to a lower speed.  I'm not aware of any way to do 
this aside from using a large burst size.