[LARTC] rate limited pfifo_fast?

[LARTC] rate limited pfifo_fast?

[Kevin O'Connor]

Hi,

I have a cable modem with a bandwidth capped upload rate.  I'd like to
prioritize packets going outbound according to the TOS header of the IP
field.  I've read through the LARTC Howto several times, and I think I have
a good feel for the information it it.  It also seems that what I'm trying
to do is pretty straight-forward and common.  Unfortunately, the HOWTO
doesn't seem to have a good answer for this simple problem, nor have I been
able work out how to do this from wading through a lot of other
documentation.

It appears that the pfifo_fast qdisc has most of what I want - prioritizing
by TOS header.  Unfortunately, it is a "work conserving" queue, and won't
work with my cable modem unless I can artificially slow down the link.

The tbf qdisc seems like it has the second part of what I want - an
artificial upload cap.  Unfortunately, it doesn't do prioritizing.  I'm
using just the tbf qdisc right now with decent results, but it still isn't
exactly what I want - sometimes bulk connections will cause latency for
interactive sessions and I find that my maximum upload rate is slightly
impaired on bulk connections.

So the question is, how do I successfully combine the above two qdiscs?

Ideally, I'd like to have three queues (interactive, normal, and bulk) like
pfifo_fast has, with maximum latencies (or queue size) for each of the
queues (eg, 50ms, 100ms, 500ms respectively).  And then prioritize the
queues so that interactive data is always taken first and bulk data last.

It would seem the htb qdisc has what I want.  Unfortunately, the
documentation (in both the howto and the htb website) all describe
complicated scenarios where I need something much simpler.  Also, I can't
seem to find the answer to simple questions like - how do I set the maximum
queue size (and/or maximum latency) for a qdisc that is a child of an HTB
qdisc?

Any help would be appreciated.  If I can get this going, I'd be happy to
contribute a section in the HOWTO for this.  (And, I think it would make a
good addition as this seems like a common task.)

-Kevin

-- 
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 | Kevin O'Connor                     "BTW, IMHO we need a FAQ for      |
 | kevin@koconnor.net                  'IMHO', 'FAQ', 'BTW', etc. !"    |
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Re: [LARTC] rate limited pfifo_fast?

[Stef Coene]

On Tuesday 16 September 2003 09:21, Kevin O'Connor wrote:
> Hi,
>
> I have a cable modem with a bandwidth capped upload rate.  I'd like to
> prioritize packets going outbound according to the TOS header of the IP
> field.  I've read through the LARTC Howto several times, and I think I have
> a good feel for the information it it.  It also seems that what I'm trying
> to do is pretty straight-forward and common.  Unfortunately, the HOWTO
> doesn't seem to have a good answer for this simple problem, nor have I been
> able work out how to do this from wading through a lot of other
> documentation.
>
> It appears that the pfifo_fast qdisc has most of what I want - prioritizing
> by TOS header.  Unfortunately, it is a "work conserving" queue, and won't
> work with my cable modem unless I can artificially slow down the link.
>
> The tbf qdisc seems like it has the second part of what I want - an
> artificial upload cap.  Unfortunately, it doesn't do prioritizing.  I'm
> using just the tbf qdisc right now with decent results, but it still isn't
> exactly what I want - sometimes bulk connections will cause latency for
> interactive sessions and I find that my maximum upload rate is slightly
> impaired on bulk connections.
>
> So the question is, how do I successfully combine the above two qdiscs?
>
> Ideally, I'd like to have three queues (interactive, normal, and bulk) like
> pfifo_fast has, with maximum latencies (or queue size) for each of the
> queues (eg, 50ms, 100ms, 500ms respectively).  And then prioritize the
> queues so that interactive data is always taken first and bulk data last.
>
> It would seem the htb qdisc has what I want.  Unfortunately, the
> documentation (in both the howto and the htb website) all describe
> complicated scenarios where I need something much simpler.  Also, I can't
> seem to find the answer to simple questions like - how do I set the maximum
> queue size (and/or maximum latency) for a qdisc that is a child of an HTB
> qdisc?
You can add a htb qdisc and 1 class.  And attach the pfifo_fast to the class.  
So the htb class will limit the traffic and the pfifo_qdisc will prioritize 
the packets.

Stef

-- 
stef.coene@docum.org
 "Using Linux as bandwidth manager"
     http://www.docum.org/
     #lartc @ irc.openprojects.net

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