Re: [LARTC] HTB not that exact

[bert hubert <ahu@ds9a.nl>]

On Thu, Dec 06, 2001 at 08:28:07PM +0100, Stefan Rompf wrote:
> Hi,
> 
> I'm experimenting using the HTB queueing discipline for traffic shaping.
> However, it is not really exact. Currently, I try this setup:
> 
> tc qdisc add dev eth0 root handle 1: htb default 3
> 
> tc class add dev eth0 parent 1: classid 1:1 htb rate 20Mbit burst 4kB
> tc qdisc add dev eth0 parent 1:1 sfq

Raise burst, for 20Mbit it needs to be at least 20kbyte!

> The network adaptor is connected to a 100MBit switch. When testing with
> netio, I can send up to 370kB/sec through class 1:2 and up to 2,4MB/sec
> via class 1:1, both measured by one/multiple instances of netio and the
> rate output of "tc -s class dev eth0". This effect occurs with Linux
> 2.4.16,  kernel either compiled with HZ set to 100 or 1024, and of

The rate output of tc -s class is not that reliable. 

> tbf seems not to be able to do exact rate limiting, too. Anything wrong
> in my configuration, or am I just taking false statistics?

Both I think. There are some indications that raising HZ may not work, as it
may not raise the resolution of the timers in the Linux Kernel - I am
investigating this! So try keeping HZ stable, and raising the size of your
bucket.

Regards,

bert

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