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 12:41:59 +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 18:32 +0800, Ming Lei wrote:

> After testing on beagle-xm, the patch is good and network is OK, but
> iperf performance is still no improvement, see below:
> 
> [root@root]#iperf -c 192.168.0.103 -w 131072 -t 10
> ------------------------------------------------------------
> Client connecting to 192.168.0.103, TCP port 5001
> TCP window size:   256 KByte (WARNING: requested   128 KByte)
> ------------------------------------------------------------
> [  3] local 192.168.0.119 port 46776 connected with 192.168.0.103 port 5001
> [ ID] Interval       Transfer     Bandwidth
> [  3]  0.0-10.0 sec  41.4 MBytes  34.7 Mbits/sec
> 

I fear there are copies in the tx path as well, in smsc95xx_tx_fixup()

Could you add traces in this function to check if skb_copy_expand() is
called ?