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Old 7th January 2011
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Carpetsmoker Carpetsmoker is offline
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Default How big are the buffers in FreeBSD drivers?


It is a set of articles he wrote over several months and is not finished writing as of this writing (if you are deeply interested in it go and read them, the most interesting ones are from December and January and the comments to the articles are also contributing to the big picture). Basically he is telling that a lot of network problems users at home (with ADSL/cable or WLAN) experience are because buffers in the network hard*ware or in operating systems are too big. He also proposes workarounds until this problem is attacked by OS vendors and equipment manufacturers.

Basically he is telling the network congestion algorithms can not do their work good, because the network buffers which are too big come into the way of their work (not reporting packet loss timely enough respec*tively try to not lose packets in situations where packet loss would be better because it would trigger action in the congestion algorithms).
Everyone seems to think that big buffers are good, but the truth is more subtle it would seem ...

Interesting read.
UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things.
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Old 8th January 2011
J65nko J65nko is offline
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See http://gettys.wordpress.com/2010/12/...d-bufferbloat/
You don't need to be a genius to debug a pf.conf firewall ruleset, you just need the guts to run tcpdump
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Old 8th January 2011
BSDfan666 BSDfan666 is offline
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OpenBSD's network drivers are transitioning to an interface called MCLGETI, it dynamically allocates mbufs (..BSD network packet buffers) for the RX rings and also attempts to provide mitigation under high loads.

Also, the default TCP receive/send window sizes are small.. a lot smaller than what some other OS's use now, and I believe 4.8 introduced window scaling so in (..most) cases it just does the Right Thing (TM).

At least on OpenBSD/i386, KVA (..kernel/supervisor space) is approximately only 512M of virtual memory.. they tend to make sure that memory isn't being wasted.
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Old 10th January 2011
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Oliver_H Oliver_H is offline
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There is a follow-up to the original article: http://www.leidinger.net/blog/2011/0...cn-in-freebsd/

After reading Jim Gettys investigations about the problems current buffer sizes of network equipment provoke (which may even have implications in the net neutrality debate), I had a look at which active queue management (AQM) algorithms with or without explicit congestion notification (ECN) FreeBSD supports.
use UNIX or die :-)
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