Pipe queues

[Peter Jeremy]

On Tue, Dec 11, 2007 at 12:31:00PM +0400, rihad wrote:
>Peter Jeremy wrote:
>> On Tue, Dec 11, 2007 at 09:21:17AM +0400, rihad wrote:
>>> And if I _only_ want to shape IP traffic to given speed, without 
>>> prioritizing anything, do I still need queues? This was the whole point.
>> No you don't.  I'm using pipes without queues extensively to simulate
>> WANs without bothering with any prioritisation.
>
>Great! One fine point remains, though:
># ipfw pipe 1 config bw 128Kbit/s
>will use a queue of 50 slots by default. What good are they for, if I 
>didn't ask for queuing in the first place?

'queue' is used in two distinct ways within the ipfw/dummynet code:
1) There's a "queue" object created with 'ipfw queue NNN config ...'
   This is used to support WF2Q+ to allow a fixed bandwidth to be
   unevenly shared between different traffic types.
2) There is a "queue" option on the "pipe" object that defines a FIFO
   associated with the pipe.

I had assumed you were talking about the former (and my response was
related to this) but given your latest posting, and having re-read the
thread, I suspect I may have been wrong.  Whilst I don't use queue
objects, I do use the queue option on my pipes.

In your example, you have a pipe that can handle 128kbps (16kBps).  If
you write a 1600byte packet to it, then the packet will reappear
100msec later.  Any further packets written to that pipe during that
time will be dropped if they can't be placed on a queue.  The
practical throughput depends on the number of queue slots available
and the number of writers.  I suggest you do some reading on queueing
theory for the gory details.

-- 
Peter Jeremy
Please excuse any delays as the result of my ISP's inability to implement
an MTA that is either RFC2821-compliant or matches their claimed behaviour.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-net/attachments/20071211/7cd55042/attachment.pgp