From owner-freebsd-net@FreeBSD.ORG  Fri Nov 28 19:36:09 2008
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To: Rui Paulo <rpaulo@fnop.net>
In-reply-to: Your message of "Fri, 28 Nov 2008 15:36:45 GMT."
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Date: Fri, 28 Nov 2008 19:36:04 +0000
From: David Malone <dwmalone@maths.tcd.ie>
Message-ID: <200811281936.aa78374@walton.maths.tcd.ie>
Cc: freebsd-net@freebsd.org, Kevin Oberman <oberman@es.net>
Subject: Re: FreeBSD Window updates 
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> Yes, this makes sense. Probably this is a bug since 4.4BSD-Lite.

I had a look to see what Linux does - it only generates pure window
updates in the case that the advertised window would change by a
factor of two. I guess this practically eliminates these updates.

I would guess that changing the code to update on a change of a
power of two would be OK. Another option would be to change the
current limit of two MSSes to three, because this would eliminate
window updates between regular delayed ACKs.

> So, from what I understand, we do back off and that implies we are  
> losing performance in the FreeBSD to FreeBSD case, right?

We do the right thing and ignore these pure window updates. I've
checked, and Linux also ignores ACKs that just seem to update the
window.

	David.