[Xen-users] Issue using tc tbf with inter-vm transfers

[Nathan March <nathan@xxxxxxxxxxxxxxxxxxxx>]

 Hi All,

Trying to setup packet shaping, everything works great for this one rule:

tc qdisc add dev vif1.0 root tbf rate 10Mbit burst 1Mb latency 20ms

Should restrict incoming traffic vif1.0 to 10mbit, pretty 
straightforward. Works great when downloading from another server and 
properly caps it off at 1.2MB/s. If I try a transfer from another vm on 
the same dom0 however, it tops out at ~ 32KB/s.  Adjusting values seems 
to have no relation on speed, it always ends up at the same ~32KB/s.
Vif1.0 in this case is the limited vm, vif2.0 is unlimited. There are no 
tc/iptables rules in place here asides from the one listed above.
xen1 ~ # tc -s qdisc show dev vif1.0
qdisc tbf 801b: root rate 10000Kbit burst 1024Kb lat 20.0ms
 Sent 42399193 bytes 29470 pkt (dropped 666, overlimits 51352 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0

xen1 ~ # tc -s qdisc show dev vif2.0
qdisc pfifo_fast 0: root bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
 Sent 262594 bytes 3063 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0

Normally I'd assume it's something I'm doing with wrong TC, except for 
the fact it works fine with external servers as well as VM's on a 
different dom0. Anyone have any insight?
- Nathan

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