[Click] Problems with RatedUnqueue

[Bart Braem]

Hello,

On 06 Feb 2009, at 13:50, Øivind Kure wrote:

> 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.


This reminds me of a bug we have seen where tasks caused high CPU usage.
Try updating to the latest git release to be sure that this is not a  
bug that is already fixed. If this fixes the problem, compare the  
implementations of RatedUnqueue.
Otherwise, it would be interesting to see output from a profiler.

Regards,
Bart Braem
-- 
Bart Braem
PATS research group - IBBT
Dept. of Mathematics and Computer Sciences
University of Antwerp
Campus Middelheim, G3.30
Middelheimlaan 1
B-2020 Antwerpen, Belgium
Phone: +32 (0)3 265.32.91
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