netdev - RE: A Linux TCP SACK Question

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Message-ID: <Pine.LNX.4.64.0804080007020.20936@wrl-59.cs.helsinki.fi>
Date:	Tue, 8 Apr 2008 09:36:44 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Wenji Wu <wenji@...l.gov>
cc:	'Sangtae Ha' <sangtae.ha@...il.com>,
	'John Heffner' <johnwheffner@...il.com>,
	'Netdev' <netdev@...r.kernel.org>
Subject: RE: A Linux TCP SACK Question

On Mon, 7 Apr 2008, Wenji Wu wrote:

> >I don't think reorderings frequently happened in your directly
> >connected networking scenario. Please post your tcpdump file for
> >clearing out all doubts.
> 
> https://plone3.fnal.gov/P0/WAN/Members/wenji/tcp_dump_files_sack/
> 
> Two tcpdump files: one with SACK on, the other with SACK off. The test
> configures described in my previous emails.

NewReno never retransmitted anything in them (except at the very end of 
the transfer). Probably something related to how tp->reordering behaves
I suppose...

ijjarvin@...nthope:~/linux/debug$ /usr/sbin/tcpdump -n -r nosack | grep 
"4888[35] >" | cut -d ' ' -f 7- | cut -d ':' -f 1 | awk '{if ($1 < old) 
{print $1}; old=$1;}'
reading from file nosack, link-type EN10MB (Ethernet)
1
641080641
ijjarvin@...nthope:~/linux/debug$ 

ijjarvin@...nthope:~/linux/debug$ /usr/sbin/tcpdump -n -r sack | grep 
"4888[35] >" | cut -d ' ' -f 7- | cut -d ':' -f 1 | awk '{if ($1 < old) 
{print $1}; old=$1;}'
reading from file sack, link-type EN10MB (Ethernet)
1
7265
10161
141929
175233
196953
446558881
3542223511
ijjarvin@...nthope:~/linux/debug$ 


This is probably far fetched but could you tell us how you make sure that 
earlier connection's metrics are not affecting the latter connection? 
Ie., the discovered reordering is not transferred across the flows (in CBI 
like manner) and thus newreno has unfair advantage?

-- 
 i.
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