netdev - TSO trimming question

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Message-ID: <Pine.LNX.4.64.0712192336130.27945@kivilampi-30.cs.helsinki.fi>
Date:	Wed, 19 Dec 2007 23:46:33 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: TSO trimming question

Hi all,

I'm not fully sure what's purpose of this code in tcp_write_xmit:

                       if (skb->len < limit) {
                               unsigned int trim = skb->len % mss_now;

                               if (trim)
                                       limit = skb->len - trim;
			}

Is it used to make sure we send only multiples of mss_now here and leave 
the left-over into another skb? Or does it try to make sure that
tso_fragment result honors multiple of mss_now boundaries when snd_wnd
is the limitting factor? For latter IMHO this would be necessary:

			if (skb->len > limit)
				limit -= limit % mss_now;

-- 
 i.
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