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From: Sean Bruno <seanbru@yahoo-inc.com>
To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>
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Date: Wed, 27 Oct 2010 11:27:02 -0700
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Subject: Excessive Duplicate ACKs
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We moved an application stack from BSD4(BOO!) to BSD7(YAY!) recently and
got a great performance increase, so first:  GOOD JOB.

Periodically, we are seeing strings of duplicate ACK being sent in
<100uSec deltas.  I can't imagine that this should be happening, but
there it is.  I've sanitized an example trace of a transaction,
demonstrating an average case that had 8 dup ACKs, some less than 3
microsends in delta!  sysctl -a also attached (and sanitized).

http://people.freebsd.org/~sbruno/dup_ack_collapsed.txt

http://people.freebsd.org/~sbruno/sysctl_dup_acks.txt


Sean