netdev - Re: [PATCH net-2.6 0/3]: Three TCP fixes

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Message-Id: <20071205.023030.125862645.davem@davemloft.net>
Date:	Wed, 05 Dec 2007 02:30:30 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	jheffner@....edu
Cc:	ilpo.jarvinen@...sinki.fi, netdev@...r.kernel.org
Subject: Re: [PATCH net-2.6 0/3]: Three TCP fixes

From: John Heffner <jheffner@....edu>
Date: Tue, 04 Dec 2007 13:42:41 -0500

> Ilpo Järvinen wrote:
> > ...I'm still to figure out why tcp_cwnd_down uses snd_ssthresh/2
> > as lower bound even though the ssthresh was already halved, 
> > so snd_ssthresh should suffice.
> 
> I remember this coming up at least once before, so it's probably worth a 
> comment in the code.  Rate-halving attempts to actually reduce cwnd to 
> half the delivered window.  Here, cwnd/4 (ssthresh/2) is a lower bound 
> on how far rate-halving can reduce cwnd.  See the "Bounding Parameters" 
> section of <http://www.psc.edu/networking/papers/FACKnotes/current/>.

I assume we're talking about the tcp_cwnd_min() usage in
tcp_cwnd_down(), I don't see where it's dividing by two
there.

Anyways, someone please enlighten me and please also cook
up a patch to add the descriptive comment :-)

Thanks!
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