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Date: Thu, 29 Jul 2004 23:55:08 -0600 (MDT)
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To: freebsd-hackers@freebsd.org, pawmal-posting@freebsd.lublin.pl
From: "M. Warner Losh" <imp@bsdimp.com>
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cc: max@love2party.net
Subject: Re: Ready or not?
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In message: <20040729201909.GA12370@shellma.zin.lublin.pl>
            Pawel Malachowski <pawmal-posting@freebsd.lublin.pl> writes:
: On Wed, Jul 28, 2004 at 03:02:38PM +0200, Max Laier wrote:
: 
: Hello,
: 
: > as PF+ALTQ gateway in production environment. For ALTQ there is the problem 
: > of "will your driver be supported?".
: 
: Could You please explain a bit, why ALTQ model is placed so close
: to network adapter driver (that they have to be modified) instead
: of placing it in upper layers (and leaving NIC drivers untouched)?

The short answer is because there is buffering (queueing) in the NIC
layer, and that limits the ability of of ALTQ to do its job.  In order
to do QoS type things, this queueing makes it harder without the help
of the NIC driver.  It is more complicated than this (I don't
understand all the details), but that is the jist of a larger
presentation of ALTQ that I had the pleasure of viewing at
AsiaBSDcon.

Warner