[Click] Problems with RatedUnqueue

[Øivind Kure]

Hi,
I run click in userspace (on a Suse 10.0 machine), essentially as a link emulator.
The essence of the configuration is Fromdevice ->Queue -> shaper -> Todevice.
In addition I use  a standard setup with Classifier, IPClassifier, CheckIPHeader, ArpResponder and ArpQuerier, so the configuration acts as a forwarding element.

For the shaper element I started out with RatedUnqueue . 
The configuration is used in a controlled environment where the load is  1,5 Mbit/sec MPEG2 video or roughly 150 packets a second.  The configuration works with no problem. However, when I reduce the rate of the shaper element (f. ex 30) , the configuration become CPU bound. Packets are dropped from the video, but the queuing element before the shaper reports 0 drops. The cpu load reported by top increases to 0% idle and almost 100% to click. The machine remains cpu bound until the rate in the shaper element is increased to 250, well above the offered load.
This problem has been observed for click 1.5 and click 1.6.  I have also observed similar problems on other linux versions.

If I replace the shaper element with Burster ( which is timer based) , the problem disappears. When the rate in the shaper element  is reduced, the queue starts dropping packets, as is shoul. The cpu load remains almost constant and low.

It might be designed feature I have missed, a bug, or I might have misunderstood something basic. Any explanation to the observed behaviour will be appreciated. 
Regards
Øivind Kure