Date: Sat, 29 Nov 2008 07:59:54 -0800 (PST) From: Venkat Venkatsubra <venkatvenkatsubra@yahoo.com> To: David Malone <dwmalone@maths.tcd.ie>, Rui Paulo <rpaulo@fnop.net> Cc: freebsd-net@freebsd.org, Kevin Oberman <oberman@es.net> Subject: Re: FreeBSD Window updates Message-ID: <88524.13498.qm@web58307.mail.re3.yahoo.com> References: <200811281936.aa78374@walton.maths.tcd.ie>
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Looking at some very old versions (4.3 BSD Reno for instance),=0Athe regula= r acks used to be=A0sent only through these=A0window updates.=0Ai.e. acks w= ere sent only when the apps read the data. Acks are piggybacked=0Awith wind= ow updates. Or, delayed till the delayed ack timer expires if the apps=0Ais= not reading. This would have had other issues with congestion control due = to generating=0Atoo few acks. When this was changed to send acks independen= t of apps reading the data,=0Awe=A0now have lot more acks due to these wind= ow updates in addition to the regular acks.=0A=0AVenkat=0A=0A=0A___________= _____________________=0AFrom: David Malone <dwmalone@maths.tcd.ie>=0ATo: Ru= i Paulo <rpaulo@fnop.net>=0ACc: freebsd-net@freebsd.org; Kevin Oberman <obe= rman@es.net>=0ASent: Friday, November 28, 2008 1:36:04 PM=0ASubject: Re: Fr= eeBSD Window updates=0A=0A> Yes, this makes sense. Probably this is a bug s= ince 4.4BSD-Lite.=0A=0AI had a look to see what Linux does - it only genera= tes pure window=0Aupdates in the case that the advertised window would chan= ge by a=0Afactor of two. I guess this practically eliminates these updates.= =0A=0AI would guess that changing the code to update on a change of a=0Apow= er of two would be OK. Another option would be to change the=0Acurrent limi= t of two MSSes to three, because this would eliminate=0Awindow updates betw= een regular delayed ACKs.=0A=0A> So, from what I understand, we do back off= and that implies we are=A0 =0A> losing performance in the FreeBSD to FreeB= SD case, right?=0A=0AWe do the right thing and ignore these pure window upd= ates. I've=0Achecked, and Linux also ignores ACKs that just seem to update = the=0Awindow.=0A=0A=A0=A0=A0 David.=0A_____________________________________= __________=0Afreebsd-net@freebsd.org mailing list=0Ahttp://lists.freebsd.or= g/mailman/listinfo/freebsd-net=0ATo unsubscribe, send any mail to "freebsd-= net-unsubscribe@freebsd.org"=0A=0A=0A=0A
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