excessive TCP dulplicate acks revisted

Gregory Wright gwright at antiope.com
Mon Nov 12 09:45:59 PST 2007

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?


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