Re: network queue lengths

[Michael Richardson <mcr%sandelman.ottawa.on.ca@localhost>]

>>>>> "David" == David Young <dyoung%pobox.com@localhost> writes:
    David> If a NetBSD box is the Internet gateway for several 10-,
    David> 100-, or 1000-megabit clients, and the clients share a 1-,
    David> 2-, or 3-megabit Internet pipe, it is easy for some outbound
    David> stream to fill both the Tx ring (max 64 packets) and the

  Hmm. maybe this explains the problems on my home network.... almost
full /25 of (mostly virtual) hosts behind a 4M/800K pipe.

    David> Now, suppose that we shorten the interface queue, or else we
    David> "shape" traffic using ALTQ.  Outbound traffic nevertheless
    David> spends 1/4 to 3/4 second on the Tx ring, which may defeat
    David> ALTQ prioritization in some instances.

    David> This is getting a bit long, so I am going to hastily draw
    David> some conclusions.  Please tell me if I am way off base:

    David> 1 in order for ALTQ to be really effective at controlling
    David> latency for delay-sensitive traffic, it has to feed a very
    David> short Tx ring

  Yes.
  Can we do this dynamically in some way? Does WRED help here?

    David> 2 maximum queue/ring lengths in NetBSD are tuned for very
    David> high-speed networks, now; the maximums should adapt to hold
    David> down the expected delay while absorbing momentary overflows.

  I would be happy to tell ifconfig some value, since it's not the link
speed that counts... 

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]   Michael Richardson, Sandelman Software Works, Ottawa, ON    |net architect[
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