[lwip-users] PPPoS TCP unix port terribly slow

[Mednyy Alexey]

Hello list!

I'm trying to implement port forwarding over LWIP.

One side is Linux x86_64 machine another one is FreeRTOS ARM device.

I have LWIP stack on both sides of PPPoS channel, and data transfers ok.
tty read/write is fast and stable.

On IP level I see that ping example app works well, I can ping opposite
side with raw sockets API and it takes about 12ms over PPPoS on 115200
baudrate.

However when I start to use TCP level things goes terribly slow. Even
simple echo server takes several seconds receive an answer.

I use default lwipopts from
lwip-contrib/examples/example_app/lwipopts.h, just added PPP_SERVER and
PPP_NOTIFY_PHASE support.

Here is my log https://pastebin.com/raw/tfwY1rtV

And lwipopts.h https://pastebin.com/vd2DrxYJ

Can somebody tell me what is wrong with my log/config?

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Best regards, Mednyy Alexey.