[LARTC] calculating burst for TBF

[LARTC] calculating burst for TBF

[Andreas Hasenack]

I'm using tc from iproute-2.6.15 with a 2.6.12 kernel.

I was testing the effects of the burst parameter in a tbf qdisc.
Basically, I was testing this statement from the tc-tbf(8) manpage:

"If your buffer is too small, packets may be dropped because more tokens arrive
per timer tick than fit in your bucket.  The minimum buffer size can be
calculated by dividing the rate by HZ."

So, for a 200kbit rate on intel, this would yeld me a minimum burst of 2000bits, or
250 bytes.

I then do this:
tc qdisc add dev eth0 handle 1: root tbf latency 50ms burst 250b rate 200kbit

but all packets are dropped. I then rise burst to 300b, 400b, even 900b and it
is still not working. It only starts working when I raise it to 2000b. Which,
besides being the wrong unit (bits versus bytes), is the result of the rate/HZ
calculation.

The tc(8) manpage says that "b or a bare number = bytes", but it seems this parameter
ends up being bits? If not, what is wrong then?

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