Date: Mon, 19 Nov 2007 13:36:37 -0500 From: Gregory Wright <gwright@antiope.com> To: Andre Oppermann <andre@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: excessive TCP dulplicate acks revisted Message-ID: <B33B08C6-72F7-4893-98AB-FA916F63FCE7@antiope.com> In-Reply-To: <473CDDAC.9020503@freebsd.org> References: <46B41421-3112-40C6-84D9-094FA771F93E@antiope.com> <4735CE3A.7020905@freebsd.org> <C621C4E4-4230-4658-B668-A0612B632565@antiope.com> <473780DB.2040705@freebsd.org> <17995F62-7E9B-42E3-A7FA-30143C704C34@antiope.com> <473CDDAC.9020503@freebsd.org>
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> Gregory Wright wrote: >> On Nov 11, 2007, at 5:23 PM, Andre Oppermann wrote: >>> Gregory Wright wrote: >>>> On Nov 10, 2007, at 10:28 AM, Andre Oppermann wrote: >>>>> >>>> Hi Andre, >>>> I also took a look at the bge (4) driver in 7.0-BETA2. As far >>>> as I can tell, >>>> it does not support TSO (there is no ioctl supporting TSO enable/ >>>> disable >>>> as there is for the em(4) driver). >>> >>>> Might the chip --- a BCM5704_B0 --- not be completely >>>> initialized? This >>>> might explain why the machine with the BCM5714_B3 chips works, >>>> while >>>> the other machine shows the duplicate ACK bug. >>> >>> Perhaps. Do you see the duplicate ACKs in a tcpdump on both the >>> sender >>> and the receiver? If you see it on the sender too, then it must >>> be a >>> bug in our network stack or the driver (by requeuing the same packet >>> over and over again). >>> >>> --Andre >> The logs show that the duplicate ACKs are generated only by the >> receiver. I suspect a bug in the driver, perhaps the ACK packet >> is not being removed from the TX buffer ring. Examining the >> transmitted >> packets should be enough to rule out a network stack problem. Is >> there any debugging infrastructure I can use or do I just have to >> hack in on my own? > > We don't have an infrastructure to deal with this kind of driver > problems. You have to instrument the driver code to report stuck > mbufs. > Hi Andre, I have some additional information that indicates this is a driver bug. There was a report to one of the Gentoo linux mailing lists of the same problem with BCM5704s, in which everything worked at 1 Gb/s, but duplicate ACKs were seen at 100 Mb/s. Link to the message: http://forums.gentoo.org/viewtopic-t-530707-highlight-bcm5704.html The report said that the problem was solved by upgrading the linux kernel from 2.6.17 to 2.6.18. I've compared the tg3 drivers in the two releases are were quite a few changes, so it will take a while to track down what the key fix was. So the bug in the bge driver for these chips can likely be fixed. Thanks for your help. Best Wishes, Greghome | help
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