[lwip-users] Delayed Ack causing problems, where to call tcp_nagle_disable()?

[Richard Barry]

Hi,

lwIP V1.4.0.

I have moved the demo FreeRTOS example from the Windoze simulator onto
real hardware in order to check the timing behaviour (which can't really
be done in the simulator), and found a timing problem.

Using an umodified raw http server from the contrib distribution, I am
attempting to retrieve a large jpg file (approx 37K).  The file is
retrieved in tact, but very slowly.  I am using a point to point connection.

Taking a Wireshark log I see that data is only being sent by lwIP  after
an ACK from Windows.  I have attached the log for good measure.
192.168.0.200 is the lwIP end.

I have considered three things to fix this.  First I have set
TCP_SND_QUEUELEN to (8 * TCP_SND_BUF/TCP_MSS), but that made no
difference.  Second I considered the calls to tcp_output() after
tcp_write() to make sure data is actually going out immediately, but
don't think that is the issue as I'm using an unmodified HTTP server
from the contrib distribution.

Finally, I want to try disabling the nagle algorithm, and see this can
be done by calling tcp_nagle_disable(), but I am unsure where and how to
do this?  I don't want to modify the core lwIP code, so assume it should
be in the http server code.  It is using the raw API version, so it is
not obvious how or where to do to call the macro correctly.

I would be grateful for advise or an example.  Thanks.


Regards,
Richard.

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