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priq and bandwidth definition



I have a similar setup to what Daniel specifies in
http://www.benzedrine.cx/ackpri.html but have a nagging question that
I haven't been able to find an answer for.
Why do you need to specify bandwidth on the parent queue in order for
the prioritizations to work correctly?  Shouldn't the packet scheduler
always transmit higher priority packets before lower priority packets
regardless of the bandwidth cap that is specified?  In my situation,
the 'lowdelay' SSH sessions are unbearably slow unless I set my
bandwidth down to 300Kb.  Of course this solves the problem of poor
interactive SSH performance, but it means I am sacrificing ~200Kb of
potential speed in order to attain that.
The parser accepts the following lines
altq on $ext_if priq queue {default, torrent}
   queue default priority 15 priq (default)
   queue torrent priority 1 priq (red)
..
pass out quick on $ext_if from any to any keep state queue (torrent, default)
and the documentation says that if a limit is not specified, it will
simply use the maximum rate of the interface specified (which I think
is translated into 100 mbit in my case).  This interface connects to a
cable modem that has roughly 4mbit down so of course that 100 mbit
assumption isn't quite right.
I have tried the other schedulers, but can't think of why a simple
weighted queueing shouldn't work for me.  Can anyone explain this to
me?
Matt