netdev - RE: RE: A Linux TCP SACK Question

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Date:	Tue, 15 Apr 2008 12:55:24 -0500
From:	Wenji Wu <wenji@...l.gov>
To:	'John Heffner' <johnwheffner@...il.com>
Cc:	'Ilpo Järvinen' <ilpo.jarvinen@...sinki.fi>,
	'Netdev' <netdev@...r.kernel.org>
Subject: RE: RE: A Linux TCP SACK Question



>We can see that in both cases you are getting throttled by
>tcp_moderate_cwnd (X_OtherReductionsCM).  I'm not sure offhand why
>it's reaching this code - I would have thought that the high
>tp->reordering would prevent this.  Ilpo, do you have any insights?

>It's not all that surprising that packets_in_flight is a higher value
>with newreno than sack, which would explain the higher window with
>newreno.

>Wenji, the web100 kernel has a sysctl - WAD_MaxBurst.  I suspect it
>may make a significant difference if you set this to a large value.

It is surprising! When I increase WAD_MaxBurst (Patched with Web100) from 3
to 20, the throughput in both cases (SACK ON/OFF) will saturate the 1Gbps
Link!!!


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