[LARTC] bandwidth limit

[LARTC] bandwidth limit

[Rendel, Thorsten]

Hi,
i am using the CBQ Qdisc as a shaper for my 100Mbit/s Ethernet LAN. 
I want to limit a bounded, isolated CBQ Class to 10 Mbit/s.
# TC class add dev $DEVICE handle X:0 classid X:Y cbq bandwidth 100Mbit/s rate 10 Mbit/s prio bounded isolated avpkt 1000 allot 1514 weight 1 maxburst 15
In my testbed i use a SmartBit Hardware traffic generator to generate traffic streams, with different protcols and different paket length. I send a UDP traffic stream with 20 Mbit/s.
The results of my measurementes are that for a paket length of 1518 Bytes the shaping works fine, but for a length of 64 Byte the shapings works very bad. I got at the outgoing interface a bandwidth of 4 Mbit/s.
I changed the avpkt, maxburst and allot parameter, but the results didn´t become better.
 What is the reson for this behavior?

Thanx
Thorsten

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Re: [LARTC] bandwidth limit

[Stef Coene]

On Friday 17 May 2002 08:06, Rendel, Thorsten wrote:
> Hi,
> i am using the CBQ Qdisc as a shaper for my 100Mbit/s Ethernet LAN.
> I want to limit a bounded, isolated CBQ Class to 10 Mbit/s.
> # TC class add dev $DEVICE handle X:0 classid X:Y cbq bandwidth 100Mbit/s
> rate 10 Mbit/s prio bounded isolated avpkt 1000 allot 1514 weight 1
> maxburst 15 In my testbed i use a SmartBit Hardware traffic generator to
> generate traffic streams, with different protcols and different paket
> length. I send a UDP traffic stream with 20 Mbit/s. The results of my
> measurementes are that for a paket length of 1518 Bytes the shaping works
> fine, but for a length of 64 Byte the shapings works very bad. I got at the
> outgoing interface a bandwidth of 4 Mbit/s. I changed the avpkt, maxburst
> and allot parameter, but the results didn´t become better. What is the
> reson for this behavior?
CBQ implementation.  
It uses the packet size as an internal parameter to calculate the idle time 
of the link.  With the avpkt you set the average packet size, so if you leave 
it on 1000, the shaping is fine for packets of 1528 bytes.  If you use 
smaller packets, you should adjust avpkt (packet size of 64byte : avpkt 64 or 
even smaller).  After that, you should be able to shape the small packets 
like you want.  But I never tested it for such small packets.
Anyway, for normal traffic, avpkt = 1000 is a good choice.

Stef

-- 

stef.coene@docum.org
 "Using Linux as bandwidth manager"
     http://www.docum.org/
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