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Date:	Wed, 20 Feb 2008 10:01:18 -0500
From:	Tony Battersby <tonyb@...ernetics.com>
To:	Michael Chan <mchan@...adcom.com>
Cc:	David Miller <davem@...emloft.net>, herbert@...dor.apana.org.au,
	netdev <netdev@...r.kernel.org>, gregkh@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: TG3 network data corruption regression 2.6.24/2.6.23.4

Michael Chan wrote:
> On Tue, 2008-02-19 at 17:14 -0500, Tony Battersby wrote:
>
>   
>> Update: when I revert Herbert's patch in addition to applying your
>> patch, the iSCSI performance goes back up to 115 MB/s again in both
>> directions.  So it looks like turning off SG for TX didn't itself cause
>> the performance drop, but rather that the performance drop is just
>> another manifestation of whatever bug is causing the data corruption.
>>
>> I do not regularly use wireshark or look at network packet dumps, so I
>> am not really sure what to look for.  Given the above information, do
>> you still believe that there is value in examining the packet dump?
>>
>>     
>
> Can you confirm whether you're getting TCP checksum errors on the other
> side that is receiving packets from the 5701?  You can just check
> statistics using netstat -s.  I suspect that after we turn off SG,
> checksum is no longer offloaded and we are getting lots of TCP checksum
> errors instead that are slowing the performance.
>
>
>   
Confirmed.  With a 100 MB read/write test, netstat -s shows 75 bad
segments received, and performance in the one direction is about 5
MB/s.  When I switch to the SysKonnect NIC, netstat -s shows 0 bad
segments received, and performance is 115 MB/s.  So that solves that
mystery - there is still data corruption, but the software-computed TCP
checksum causes the bad packets to be retransmitted rather than being
passed on to the application.

Tony

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