Re: Kernel timer frequency and HTB

Andy Furniss
2007-04-04T21:42:10Z

lists@antonello.org wrote:
> Hello,
> i have a linux box which is acting as a lan router towards the internet
> doing traffic shaping.
> My link is 10Mbit/s full duplex.
>
> I have set some HTB classes with a rate of 20% (2Mbit/s) and a ceil of
> 95% (9.5Mbit/s). Is such an excursion of bandwidth in the HTB classes
> feasible for HTB to control?

I would have thought it''s OK, 9.5mbit may be a bit close to the limit
depending on what yout overheads on the link are.

>
> What Timer frequency (kernel menuconfig) is the most suitable among 250,
> 300 and 1000Hz for HTB? Also, I really don''t have any ideas on how
the
> frequency could affect the network adapter performance. Is a high
> frequency going to have bad effects on interrupts handling? Has anybody
> any suggestions about this issue?

I would say 1000 is best. An individual class needs a burst/cburst size
big enough to reach its rate/ceil so you can have smaller bursts on classes.

HTB was written when Hz=100 and unless you specify burst/quantum it will
choose them from the rates. If you do use 1000 it may be worth having a
look what it chose with tc -s -d class ls dev ....
>
> I have some warnings about HTB quantums being too big, but as i
> understand, those should only affect the precision of the shaping
> without undermining the shaping completely.

Quantum affects the way excess bandwidth is shared - you can specify it
on each line that has a rate/ceil if you want - minimum should be 1514
on eth with mtu 1500. If you don''t specify it HTB will use the rates to
set it, which may not be what you want.

Andy.