From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: TCP transmit performance regression
Date: Thu, 05 Jul 2012 10:33:12 +0200
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Cc: Network Development <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>
To: Ming Lei <tom.leiming@gmail.com>
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On Thu, 2012-07-05 at 16:27 +0800, Ming Lei wrote:

> After some investigation, the problem is caused by enabling
> DEBUG_SLAB, so it is not a regression.
> 

Strange, unless your machine is a _very_ slow one maybe ?

> 
> Looks no improvement. I still don't know why the window size becomes so
> small even in good situation(disabling DEBUG_SLAB), and the small
> window size will cause almost every tcp data packet acked.

You are probably missing the fact that window scaling is enabled.

If you dont post a pcap, I am afraid we cant really help.