Re: [LARTC] HTB: quantum vs. burst

[Pavel Mores <pvl@uh.cz>]

On Thu, Jan 16, 2003 at 08:05:24PM +0100, Stef Coene wrote:

> No.  I did some tests my self witb burst and cburst.  The problem is that it's 
> very difficult to measuer and explain it.  You have to believe Devik that it 
> works :)

I'm not saying that I don't believe him. ;)  However, bursting within
complex multilevel hierarchies can bring about a number of rather opaque
interactions.  If you need to be able to understand this (in other
words, to know what you are doing), the basic info from the docs is just
not enough.

> And burst is not made for big bursts like you did.

Yeah, I know.  I'm not saying this is a realistic scenario.  I set it
this big just to see it properly in the dumps and graphs.

> It also helps if you disable HTB_HYSTERESIS in the htb qdisc.  See faq page 
> for more info.

Take a look at the 1:76's graph if you care - see that depression
between 140.  and 170. second?  It's not there because of lack of demand
- 1:77 is still asking for bandwidth.  It's probably 1:76 retaliating
for being pushed above its ceil between 10. and 40. second.  If I
understand the docs correctly, the depression should not be there since
I *did* set 1:76's burst, too.  I was thinking about disabling
HTB_HYSTERESIS in hope that doing so would remove this problem but I
haven't tried it yet.

> > - back to your example - I'd even dare to say that the class you
> >   described wouldn't profit from setting burst at all *unless* there's
> >   another class competing for the bandwidth.  (If there is a contention,
> >   the burst setting will matter.)  Can you confirm this?
> No.  If you have a 10kbyte/s link and you have a class with ceil = rate = 
> 5kbyte/s and a big burst/cburst (100.000byte or so), you can measure the 
> burst.  The first 100.000 byte will be sended by the burst so it will be 
> sended in 10 second.

I just repeated the experiment with the exception that only 1:78 (the
one with burst set) was asking for bandwidth (the competing 1:77 was
silent) and I'm afraid that I'm not able to see any burst anyway.  In my
view, burst won't let me break my ceil. However, cburst will.

> I have some very detailed information about how the burst and cburst from 
> parent and child classes are interacting, but I still have to create a page 
> for it.  It also explains how burst and cburst can exists and how the tokens 
> and ctokens are changing when you are using the burst.  Maybe something I can 
> do tonight.  I will keep you informed.

That would be *great*. :-)

	pvl

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