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.
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