[lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Jakub Schmidtke]

Hi,

I am using lwip with NO_SYS=1, and I have noticed

that outgoing TCP packets are very delayed.

It looks like between writing a packet (using tcp_write),

and the time it actually written to the interface it takes usually about 200ms.

I examined the code, and it looks like lwip only writes regular packets every 500ms.

Basically tcp_write only adds segments to a list, and they are only actually sent inside tcp_slowtmr.

Which, by default, is only called once every two calls to tcp_tmr().

Which gets called every 250ms, so the data being written with tcp_write will be sent out up to 500ms later.

This is a really, really long time!

Am I missing something?

Thanks!