[altq:1889] Re: CBQ: small pakets are too limited !

[Luigi Rizzo <rizzo@icir.org>]

if i remember well, altq works at the device driver's level
so it probably uses the MAC frame size instead of the IP size.
The extra 18 bytes (possibly together with a min frame size
of 64 bytes) might explain the difference.

	cheers
	luigi

On Tue, Aug 19, 2003 at 04:41:24PM +0200, Emmanuel Duros wrote:
> 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
> 
> -- 
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