LARTC - Jul 2001 - rate precision of CBQ

Hi all,

I have managed some CBQ class like :

tc class add dev eth0 parent 10:1 classid 10:100 cbq bandwidth 1920KBit
rate 784 KBit allot 1514 weight 1 Kbit prio 8 maxburst 20 avpkt 1000
bounded

It works fine, but I noticed that the rate precision is not very good
(despite the bounded parameter) :

784 kBit => 96 KBytes/s (theoric) but 130-140 KBytes/s in reality
512 kBit => 64 KBytes/s (theoric) but 80-90 KBytes/s in reality
256 kBit => 32 KBytes/s (theoric) but 33-34 KBytes/s in reality

At low rate (< 256k), it seems good but not at higher rate.


Is this problem coming from my parameters (weight, prio, ...) or is it a
known problem with CBQ ?

regards,
------------------------------------------------
Franck BALAZOT (fbalazot@aeta.fr)
AETA.COM
361, Avenue du Général De Gaulle
92140 CLAMART
FRANCE
Tél:01.41.36.12.93
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Franck BALAZOT wrote:
>Hi all,
>
>I have managed some CBQ class like :
>
>tc class add dev eth0 parent 10:1 classid 10:100 cbq bandwidth 1920KBit
>rate 784 KBit allot 1514 weight 1 Kbit prio 8 maxburst 20 avpkt 1000
>bounded
>
>It works fine, but I noticed that the rate precision is not very good
>(despite the bounded parameter) :
>
>784 kBit => 96 KBytes/s (theoric) but 130-140 KBytes/s in reality
>512 kBit => 64 KBytes/s (theoric) but 80-90 KBytes/s in reality
>256 kBit => 32 KBytes/s (theoric) but 33-34 KBytes/s in reality
>
>At low rate (< 256k), it seems good but not at higher rate.
>
>
>Is this problem coming from my parameters (weight, prio, ...) or is it a
>known problem with CBQ ?
>
Try using tbf or something as a leaf qdisc.

Marian Jancar