netdev - Re: RE: A Linux TCP SACK Question

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Message-ID: <1e41a3230804151001gc9fa670p511b16bb01e0bc93@mail.gmail.com>
Date:	Tue, 15 Apr 2008 10:01:25 -0700
From:	"John Heffner" <johnwheffner@...il.com>
To:	"Wenji Wu" <wenji@...l.gov>
Cc:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: RE: A Linux TCP SACK Question

On Tue, Apr 15, 2008 at 9:39 AM, Wenji Wu <wenji@...l.gov> wrote:
>  SlowStart            0
>  CongAvoid            0
>  CongestionSignals    3
>  OtherReductions      13166
>  X_OtherReductionsCV  0
>  X_OtherReductionsCM  13166
>  CongestionOverCount  37
>  CurCwnd              10136
>
> MaxCwnd              173760
>  CurSsthresh          94894680
>  LimCwnd              4294965848
>  MaxSsthresh          94894680
>  MinSsthresh          46336

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.

  -John
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