Re: [LARTC] HTB burst, cburst parameters

[Martin Devera <devik@cdi.cz>]

On Mon, 10 Dec 2001, Stef Coene wrote:

> > Not really.
> >
> > It kills all the traffic...giving me very low thruput....i read on the HTB
> > homepage that on x86 machines burst has to be a minimum of 12K or
> > something like that.
> >
> > Whats cburst ?
> If you set cbust equal to packet size, the rate will be checked each time you 
> send cbust bytes and thus each time you send a packet.  This would be ideal 
> and you will never get a bust that exceed the ceil.  Default cburst = 2Kb/8.
> 
> But how do you get a burst?  That's why you have the burst parameter.  Each 
> time you can poll the hardware, you can change to a new class.  Devik 
> calculated the burst for a i386 on a 10mbit and it's 12kb.  So, you can send 
> 12kb, choose an other class, send an other one, choose an other class.  
> That's the fastest way you can work.  The 12kb is sended as fast as possible 
> and creates a burst.  But with the cburst parameter you can control that 
> burst.  If you specify a bigger burst parameter, you can create bigger burst, 
> but unload the CPU/hardware.
> 
> I hope I'm explained it right.  Devik ?

Almost :) The part "send 12k and select other class" is not exact.
Other class is selected also when current one is empty or DRR allotment
is exceeded.
Also cburst is not meant for burst reshaping (like peakrate in tbf)
but can be used for it.
tbf estimators always needs two parameters, rate and burst. There are
two estimators (rate and ceil) thus we have four (2*2) parameters:
rate/burst
ceil/cburst

I'm working on new patch to tc where you have not need to set
bursts. There are automaticaly computed from rate and ceil to
their smallest possible values (but you can still override them).

devik


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