[lwip-devel] [bug #20506] LWIP: TCP Layer Performance

[Simon Goldschmidt]

Update of bug #20506 (project lwip):

                Category:                     TCP => Contrib                
              Item Group:         Feature Request => Faulty Behaviour       

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Follow-up Comment #4:

BTW: Attaching an ethereal/wireshark capture file is worth much more than
only seeing the image you attached. E.g. we can see the MAC/IP/TCP headers,
maybe there are problems there?

> i observed that for a http request the time taken from the starting of
tcp_input function to function of http layer is 150ms which I think can be
improved.

That is definitively not normal! As it works fine on other platforms, I
suggest this might be a memory limitation (problem with your memory settings
in lwipopts.h)

Anyway, looking at your trace, the only real gap is between the first and
second HTTP response packet for each JPG. That might be a limitation of the
http server or of your memory.

What disturbs me is that there is no call to tcp_output in the whole httpd.c
file. Calling tcp_write simply enqueues the data to send, without calling
tcp_output, no data will be sent right away. Data will only be sent by timer
functions, which are running about every 250 ms for tcp. This is the best
explanation for your delay, after all.

This is not an error in lwIP itself, but in the http server!
As this http server is also included in our contrib module, I'm setting this
to 'Faulty Behaviour' in module 'Contrib'.

BTW: thanks for reporting this.

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