[LARTC] Kernel timer frequency and HTB

[Andy Furniss]

lists at 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.