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Re: [lwip-users] Raw TCP - PBuf segment not decreasing

From: LRA_
Subject: Re: [lwip-users] Raw TCP - PBuf segment not decreasing
Date: Mon, 18 Mar 2019 19:24:20 -0700 (MST)


Again, thank you very much. I probably am just really bad at using these
sources but I find it hard to find all the info so your help is really

So I have now a different setup, still just for testing. I think I
understand better but it looks like there is some concept I am not grasping.
So I have:
- the "main". 
- The ISRs (ethernet ISR and timer ISR)

So ethernet ISR and timer ISR should be in the same context if they have the
same priority.
The main should be like a low priority task.

In the main I have a function to send data. The function either
a) call tcp_sent() and tcp_write() if no data is loaded. This between
disabling interrupts (all for now) so it's like a priority inversion and the
ISRs should not be where they shouldn't.
b) load up my buffer - a buffer that I created for the purpose.

In the timer ISR:
- Increment lwip timer by 5.
- Call tcp_output every 10 counts, so 50ms.
- Load tcp_write if there is data available and tcp_sent callback has

With this I can see an increase in throughput though I see many lost data -
my buffer fills up too quickly.
I have tried to instead just fill my buffer when TCP snd_buf is full
(tcp_write() returns err_mem).
I am trying to find the bottle neck with no success. In wireshark I see that
never more than 2 segments are sent without an ACK. Some cases it sends 2 at
the same time, get and ACK, send other 2 just 3ms later (all with len=1460).
So this seems high enough throughput on some bursts.

I already tried with nagle enabled and disabled. With nagle disabled I had
to buffer all data into tcp_write to not run out of snd_queuelen. But it
seems to me that, since I don't quite need crazy low latency, nagle should
be enabled.

I can see some issues with my test case even for just a test. 
But not sure if I am in the right path.
This is very different from playing with tiny tests in Linux with Unix

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