netdev - Re: HTB/HSFC shaping precision

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Date:	Mon, 19 Nov 2007 11:24:54 -0500
From:	jamal <hadi@...erus.ca>
To:	Denys Fedoryshchenko <denys@...p.net.lb>
Cc:	netdev@...r.kernel.org
Subject: Re: HTB/HSFC shaping precision

Denys,

You certainly make a very compelling case. It is always compelling if
you can translate a bug/feature into $$;->.

So in your measurements, what kind of clock sources did you use?
I think the parameters to worry about are: packet size, rate and clock
source. 
I know that based on very old measurements i did on CBQ, regardless of
the clock source if you have a long-lived flow the bandwidth measurement
corrects itself. I wouldnt recommend going to CBQ, but a good start is
to test and post some results.

cheers,
jamal

On Mon, 2007-19-11 at 10:55 +0200, Denys Fedoryshchenko wrote:
> Hi 2 all again
> 
> This is not a bug report this time :-) 
> Just it is very interesting question, about using Linux "shaping" technologies
> in serious jobs.
> 
> What i realised few days ago, many ISP's set on their STM-1(155520000 bits/s)
> links (over Cisco) packet buffer/queue 40 packets(for example).
> It means 103680  pps with 1500 byte packets,  and if buffer is only 40
> packets, it means it require at least 0.3ms scheduler precision? Otherwise i
> can have buffer overflow and as result packetloss(what is much worse than
> delay in most of situations).
> 
> What i am interested - to utilise such links nearby 100%. So anything not
> precise will kill idea.
> Thats important, cause price for links in my area is about $1000-$1500 Mbit/s,
> and just 1% lost/not utilised on STM-1 is up to $2325/USD lost per month.
> I have to count also overhead, LAN jitter, and etc.
> 
> As far as i test, on HFSC if i set dmax 1ms-10ms it works much better (i am
> talking about precision) than HTB with quantum 1514 (it is over ethernet). 
> 
> Anybody have ideas what is the precision of bandwidth shaping in HFSC/HTB?


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