netdev - Re: [PATCH 01/10] tcp: collapse more than two on retransmission

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Date:	Mon, 24 Nov 2008 21:05:04 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 01/10] tcp: collapse more than two on retransmission

From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Mon, 24 Nov 2008 16:21:58 +0200

> I always had thought that collapsing up to two at a time was
> intentional decision to avoid excessive processing if 1 byte
> sized skbs are to be combined for a full mtu, and consecutive
> retransmissions would make the size of the retransmittee
> double each round anyway, but some recent discussion made me
> to understand that was not the case. Thus make collapse work
> more and wait less.
> 
> It would be possible to take advantage of the shifting
> machinery (added in the later patch) in the case of paged
> data but that can be implemented on top of this change.

Yes, the ->nr_frags test is a real limiter these days
because on any modern device all TCP data is paged,
whether sendmsg() or sendpage() generated.

So you must have used a non-SG capable device for your
tests or simply turned SG off using ethtool :)

 ...
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>

Applied, thanks!
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