netdev - Re: RE: A Linux TCP SACK Question

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Date:	Fri, 04 Apr 2008 15:07:17 -0500
From:	Wenji Wu <wenji@...l.gov>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	'John Heffner' <johnwheffner@...il.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: RE: A Linux TCP SACK Question


> On Fri, 4 Apr 2008, Wenji Wu wrote:
> 
> > Every system runs Linux 2.6.24.
> 
> You should have reported kernel version right from the beginning. It 
> may 
> have a huge effect... ;-)
> 
> > When sack is on, the throughput is around 180Mbps
> > When sack is off, the throughput is around 260Mbps
> 
> Not a surprise, once some reordering is detected, SACK TCP switches 
> away 
> from FACK to something that's not what you'd expect (in 2.6.24), you 
> should try 2.6.25-rcs first in which the non-FACK is very close to 
> RFC3517.
> 
> > I was thinking that if the reordered ACKs/SACKs cause cjavascript:parent.send('smtp')
Send Message
Sendonfusion in the
> > sender, and sender will unnecessarily reduce either the CWND or the
> > TCP_REORDERING threshold. I might need to take a serious look at the 
> 
> > SACK implementation. 
> 
> I'd suggest that you don't waste too much effort for 2.6.24. ...Most 
> of it 
> is recoded/updated since then.

Thanks, i would try it on the latest version and report the results.

wenji

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