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    SubjectRe: 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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