netdev - Re: [Bugme-new] [Bug 9031] New: TPC window is to cautious on send

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Message-Id: <20070916234340.dfe2e94e.akpm@linux-foundation.org>
Date:	Sun, 16 Sep 2007 23:43:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	netdev@...r.kernel.org
Cc:	bugme-daemon@...zilla.kernel.org, a@...ms
Subject: Re: [Bugme-new] [Bug 9031] New: TPC window is to cautious on send

On Sun, 16 Sep 2007 17:02:46 -0700 (PDT) bugme-daemon@...zilla.kernel.org wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=9031
> 
>            Summary: TPC window is to cautious on send
>            Product: Networking
>            Version: 2.5
>      KernelVersion: Any
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: IPV4
>         AssignedTo: shemminger@...l.org
>         ReportedBy: a@...ms
> 
> 
> This has been a longstanding "bug" of sorts when talking to a system that has
> extremely small windows (under 1.5k).
> 
> The only way to give the stack on the other side a nudge is to ACK twice.
> 
> Here is a sample transcript, with a max window size of 1025 bytes.
> 
> 18:25:43.968358 IP dr.ea.ms.http > 192.168.80.2.40246: . 37377:37633(256) ack
> 120 win 5840
> 18:25:43.992402 IP 192.168.80.2.40246 > dr.ea.ms.http: . ack 37121 win 769 <mss
> 256>
> 18:25:44.390305 IP 192.168.80.2.40246 > dr.ea.ms.http: . ack 37121 win 1025
> <mss 256>
> 18:25:44.823084 IP dr.ea.ms.http > 192.168.80.2.40246: . 37633:37889(256) ack
> 120 win 5840
> 
> If I take the "nudge" code out of my IP stack, it sits for an aweful long time,
> waiting on the next packet, when there clearly is room for a few more.
> 
> Should I:
> 1: Have my IP stack lie about the window till it is important?
> 2: Something else?
> 
> I can't see any good reason for the large delay, since it is on a serial link,
> via SLIP.
> 
> I can point you to source code that will allow you to verify the problem for
> yourself, if you would like.
> 

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