[altq:1887] CBQ: small pakets are too limited !

[Emmanuel Duros <emmanuel.duros@udcast.com>]

Hi,

I have a router based on FreeBSD 4.4R with altq-3.0.

My router is dedicated to route udp traffic that is shaped with altq. My
problem is that I have not been able to shape correctly udp traffic
composed of small packets (e.g. 50 to 500 byte-long). The outgoing
traffic is significantly below the bandwidth set in altq.conf.

However, when I increase the packet size, I can reach the correct
bandwidth.

Here is my setup:

Traffic           fxp0  ALTQ  xl0
generator ------------ router -------------
(UDP)

Altq conf file is:

interface xl0 bandwidth 10000000 cbq
class cbq xl0 root_class NULL pbandwidth 100
class cbq xl0 def_class root_class pbandwidth 100 default
class cbq xl0 udp_class def_class exactbandwidth 2400
	filter xl0 udp_class 0 0 0 0 17

With this configuration I would expect to see a 2.4Mbps outgoing
traffic.
However when genrating UDP packet of 50 bytes at 2.5Mbps, at the routeur
the outgoing throughput is about 1.7Mbps ! altqstat gives the following
output:
Class 0 on Interface xl0: udp_class
	priority: 1 depth: 0 offtime: 7720 [us] wrr_allot: 590 bytes
	nsPerByte: 3333	(2.40M Mbps),	Measured: 1.76M [Mbps]
	pkts: 1418941,	bytes: 137803622
	overs: 49551,	overactions: 48920
	borrows: 0,	delays: 48920
	drops: 96679604,	drop_bytes: 96679604
	QCount: 1,	(qmax: 30)
	AvgIdle: -5 [us],	(maxidle: 2512 minidle: -4999 [us])

When I increase the size of UDP pkt up to 1000 bytes, then I can reache
2.4Mbps.

How can I get the 2.4Mbps as I would expect for UDP traffic made of
small packets as well as "large" packets ????

Thanks 
Emmanuel Duros

-- 
Emmanuel Duros                  http://www.udcast.com
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