netdev - Re: TSO trimming question

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Message-Id: <20071220.040037.48002365.davem@davemloft.net>
Date:	Thu, 20 Dec 2007 04:00:37 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	netdev@...r.kernel.org, herbert@...dor.apana.org.au
Subject: Re: TSO trimming question

From: "Ilpo_Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Thu, 20 Dec 2007 13:40:51 +0200 (EET)

> That's not the only case, IMHO if there's odd boundary due to 
> snd_una+snd_wnd - skb->seq limit (done in tcp_window_allows()), we don't 
> consider it as odd but break the skb at arbitary point resulting
> two small segments to the network, and what's worse, when the later skb 
> resulting from the first split is matching skb->len < limit check as well 
> causing an unnecessary small skb to be created for nagle purpose too, 
> solving it fully requires some thought in case the mss_now != mss_cache 
> even if non-odd boundaries are honored in the middle of skb.

In the most ideal sense, tcp_window_allows() should probably
be changed to only return MSS multiples.

Unfortunately this would add an expensive modulo operation,
however I think it would elimiate this problem case.
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