netdev - TSecr != 0 check in inet

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Message-Id: <200908250054.50664.opurdila@ixiacom.com>
Date:	Tue, 25 Aug 2009 00:54:50 +0300
From:	Octavian Purdila <opurdila@...acom.com>
To:	"Jan-Bernd Themann" <themann@...ibm.com>
Cc:	netdev@...r.kernel.org, Christoph Raisch <raisch@...ibm.com>
Subject: TSecr != 0 check in inet_lro.c

Hi,

We are seeing a performance issue with TSO/LRO which we tracked down to the 
TSecr !=0 check in lro_tcp_ip_check.

It happens when the LRO side's TSval wraps around and gets to 0. That triggers 
the TSO side to send packets with TSecr set to 0, which means that such 
packets won't be aggregated - and that will put a lot of burden on the stack 
which will result in lots of drops.

I'm failing to understand the purpose of this check. Any hints? :)

Thanks,
tavi
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