Re: [lwip-users] Slow TCP

[Kieran Mansley]

On Wed, 2011-03-02 at 07:51 +1300, Bernard Mentink wrote:
> Hi Kieran,
> 
> 
> Ok, attached is a wireshark capture file.
> 
> 
> Please have a look, and let me know what you think is happening ...

Just to be sure: which end is running lwIP?  I think it's 192.168.0.100
(the http server)

A few things:
 - everything looks mostly fine for the first 10 seconds or so of the
trace.
 - then I can see the server making increasing numbers of unnecessary
retransmissions.  i.e. retransmitting packets that the client has
acknowledged as received.  This is probably the root of the problem.
 - then we start to see connections being reset by the server.  This in
itself is a bit odd, unless your server normally works by aborting
rather than closing connections.
 - the client doesn't seem to be expecting the resets, and even seems to
ignore them: it carries on trying to use those connections
retransmitting packets and so the server repeatedly replies to them with
resets.

So, yes something is wrong.  I'm not sure what though.

Could you try experimenting with fewer concurrent connections and see if
that is the trigger?  How does you web server deal with concurrent
connections?  Does it for example use multiple threads?  Which API are
you using in your web server to send and receive packets?

It would be useful if you could show us some of your code, particularly
around how your application interfaces to lwIP, and how your driver
interfaces to lwIP.  These are the most common areas for problems.

Kieran