I'm using tc with kernel 188.8.131.52 for traffic shaping. Limit bandwidth works, adding delay works, but when shaping both bandwidth with delay, the achieved bandwidth is always much lower than the limit if the limit is >1.5 Mbps or so.
tc qdisc del dev usb0 root tc qdisc add dev usb0 root handle 1: tbf rate 2Mbit burst 100kb latency 300ms tc qdisc add dev usb0 parent 1:1 handle 10: netem limit 2000 delay 200ms
Yields a delay (from ping) of 201 ms, but a capacity of just 1.66 Mbps (from iperf). If I eliminate the delay, the bandwidth is precisely 2 Mbps. If I specify a bandwidth of 1 Mbps and 200 ms RTT, everything works. I've also tried ipfw / dummynet, which yields similar results.
I've tried using rebuilding the kernel with HZ=1000 in Kconfig -- that didn't fix the problem. Other ideas?