netdev - Re: tbf/htb qdisc limitations

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Date:	Thu, 14 Oct 2010 06:44:05 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Bill Fink <billfink@...dspring.com>
Cc:	Rick Jones <rick.jones2@...com>,
	Steven Brudenell <steven.brudenell@...il.com>,
	netdev@...r.kernel.org
Subject: Re: tbf/htb qdisc limitations

On Wed, Oct 13, 2010 at 11:36:53PM -0400, Bill Fink wrote:
> On Wed, 13 Oct 2010, Jarek Poplawski wrote:
> 
> > On Tue, Oct 12, 2010 at 03:17:18PM -0700, Rick Jones wrote:
> > >>> my burst problem is the only semi-legitimate motivation i can think
> > >>> of. the only other possible motivations i can imagine are setting
> > >>> "limit" to buffer more than 4GB of packets and setting "rate" to
> > >>> something more than 32 gigabit; both of these seem kind of dubious. is
> > >>> there something else you had in mind?
> > >>
> > >>
> > >> No, mainly 10 gigabit rates and additionally 64-bit stats.
> > >
> > > Any issue for bonded 10 GbE interfaces?  Now that the IEEE have ratified 
> > > (June) how far out are 40 GbE interfaces?  Or 100 GbE for that matter.
> > 
> > Alas packet schedulers using rate tables are still around 1G. Above 2G
> > they get less and less accurate, so hfsc is recommended.
> 
> I was just trying to do an 8 Gbps rate limit on a 10-GigE path,
> and couldn't get it to work with either htb or tbf.  Are you
> saying this currently isn't possible?

Let's start from reminding that no precise packet scheduling should be
expected with gso/tso etc. turned on. I don't know current hardware
limits for such a non-gso traffic, but for 8 Gbit rate htb or tbf
would definitely have wrong rate tables (overflowed values) for packet
sizes below 1500 bytes.

> Or are you saying to use
> this hfsc mechanism, which there doesn't seem to be a man page
> for?

There was a try:
http://lists.openwall.net/netdev/2009/02/26/138

Jarek P.
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