Re: [lwip-users] Connections slowing down after some time

[Kieran Mansley]

On Fri, 2009-03-06 at 13:11 +0100, Steffen Wolfer wrote:
> Hello,
> 
> I'm using lwIP on an LPC2468 with FreeRTOS. I wrote my own little web
> server on top of lwIP, using the sockets API. Now for the first couple
> of requests, everything runs pretty fast and my web sites, which consist
> of up to six files and an overall size of at least 20 KB, are loaded
> within less than one second.
> However, after some requests everything is heavily slowing down and
> requests need up to one minute to become completely satisfied. I checked
> the lwIP stats but couldn't find any suspicious values. 

I wonder if you're ending up with buffers being used to support out-of-
order TCP segments and these aren't getting flushed properly, leading to
fewer buffers available and so drops and reduced performance.  I think
there was a bug like this recently.  What version of lwIP are you using?
Would be easy to test this by disabling OOSEG support in your lwipopts.h

> On the other
> hand I noticed that ping times before slowing down are about 0.5 ms and
> after turn pretty exactly to 1000 or 2000 ms.

In the past I've seen that when a packet has been buffered but ignored.
Receiving another packet causes an interrupt (or something) that results
in the first packet being noticed, but the second packet is then
buffered and ignored.  And so on.  Not sure if that's any help to you.

> Analyzing with wireshark, I found out that a lot of packets are re-sent
> after slowing down.

If you have a wireshark capture that is often useful to share so we can
see what's going on.

Thanks

Kieran