[Click] queue element taking high number of cpy cycles

[Shilpi Agarwal]

Hi!!

I am running a simple configuration

ss::StrideSched(100)

PollDevice(eth1,true)
->SetCycleCount()
->c0::Classifier(6/001094020740,-)

c0[0]
->CycleCountAccum()
->Strip(12)
->MacEncap(00:02:b3:b6:cA:1F,00:10:94:02:07:f6)
->CycleCountAccum()
->Queue(50)
->CycleCountAccum()
->[0]ss


c0[1]
->Discard;

ss[0]->CycleCountAccum()->ToDevice(eth1);

Now the cpucycles spent in queue are very large..and it increases with number of
packets ..here is some statistics ..


packet   packet  queue   cycles       cycles
rate     size    size    in queue     in whole forwarding patch

300k     68       100    4100.8       4836.83
300k     66       100    4287.86      5032.55
200k     66       100    2681.68      3366.0
200k     66        50    2525.57      3200

Its irrespective of queue size. Even if i increase the queue size to be 5000 or
1000 ..i get the same statistics... I am running Pentium 4 ,2 ghz machine. So
time spent in ns is half of cpu cycles .

Does anyone have any idea ..why is it so ?? I guess..since i have a queue some
of the cpu cycles are common for a fraction of packets. So it gets accumulated
more than once. Thats why if i increase packet rate i see more cpu cycles..if
thats the case..how can i measure the exact number of cpu cycles ?

Thanks
Shilpi




Shilpi Agarwal
Graduate Student
Dept of Electrical Engineering
University of Wisconsin 
Madison-53706
phone:608-233-3714