On Sun, 4 Jul 2010, Andrew Beverley wrote:
I was, in fact, an error in my ruleset. I had put the 'linklayer atm' at
both the branch and leaf levels, so the overhead was computed twice,
creating those holes in the bandwidth.
I am seeing similar behaviour with my setup. Am I making the same
mistake? A subset of my rules is as follows:
tc qdisc add dev ppp0 root handle 1: htb r2q 1
tc class add dev ppp0 parent 1: classid 1:1 htb \
rate ${DOWNLINK}kbit ceil ${DOWNLINK}kbit \
overhead $overhead linklayer atm <------- Here
tc class add dev ppp0 parent 1:1 classid 1:10 htb \
rate 612kbit ceil 612kbit prio 0 \
overhead $overhead linklayer atm <------- And here
tc qdisc add dev ppp0 parent 1:10 handle 4210: \
sfq perturb 10 limit 50
tc filter add dev ppp0 parent 1:0 protocol ip \
prio 10 handle 10 fw flowid 1:10
I removed the overhead option on the first leaf, and the speeds change
to what I expect. However, the rules above are taken straight from the
ADSL Optimizer project, which was the source of the original overhead
patch for tc. So is the ADSL Optimizer project wrong?
After looking at the HTB kernel code I believe that the ADSL Optimizer
project is NOT wrong. You should/must set the linklayer option on both
the root class and leaf (else you would be charging the root/parent node
too little).
It is the expected behavior that small packets cause a significant
reduction in the available bandwidth on the ATM link. Small packets will
(almost) always cause 2 ATM packets (being send) using 106 bytes, thus
eg. sending a 40 bytes TCP ACK packet result in approx 62% overhead.
Cheers,
Jesper Brouer
--
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MSc. Master of Computer Science
Dept. of Computer Science, University of Copenhagen
Author of http://www.adsl-optimizer.dk
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