[LARTC] Fwd: PFIFO to contain more pkts than allowed by TCP peer?

[Andy Furniss]

Daniel Schaffrath wrote:
> Maybe this is the right place to ask?
> 
> Thanks again,
> Daniel
> 
> 
> Begin forwarded message:
> 
>> From: Daniel Schaffrath <daniel.schaffrath at mac.com>
>> Date: 21 July 2007 11:01:01 GMT+02:00
>> To: linux-net at vger.kernel.org
>> Subject: PFIFO to contain more pkts than allowed by TCP peer?
>>
>> Hello everybody,
>>
>> when the one and only connection originating my box is a TCP stream 
>> which is limited by the advertised window of my peer at - lets say - 
>> 47 pkts, I would expect 'tc -s qdisc show' to show at most 47 pkts in 
>> the pfifo of the appropriate device. Unfortunately, this is not the 
>> case. It's around 83 (twice as much??). Anyone any hints how come?

Maybe tcp window scaling - you can tcpdump the syn/syn ack of the 
connection to see what if any scale factors are being used.

If pfifo is just on the root of a device rather than as a child of 
something that retelimits, then there could be 100s of packets in a 
further buffer before you even see a backlog.

Andy.