buglwIP - A Lightweight TCP/IP stack - Bugs: bug #60402, Transmitting TCP packets stops...


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bug #60402: Transmitting TCP packets stops after TCP window update is received

Submitted by:  Peter Begella <begi>
Submitted on:  Fri 16 Apr 2021 09:39:26 AM UTC
Category:  TCP Severity:  3 - Normal
Item Group:  Faulty Behaviour Status:  None
Privacy:  Public Assigned to:  None
Open/Closed:  Open Planned Release:  None
lwIP version:  * 2.1.1
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Fri 16 Apr 2021 09:39:26 AM UTC, original submission:  

Hi lwIP developers,

First of all let me thank you your work.

Unfortunately I ran into an issue on Xilinx Zynq7000 system where we use lwip211_v1_1 for transmitting large amount of data over TCP with at least 550Mbit/s throughput.
This is easily achievable (max. is 930Mbit/s) however sometimes there is a glitch somewhere which results in a 1s stop in the transmission. This happens randomly and always comes after a received a TCP Window Update packet.
The only thing I was able to figure out that there are two type of issues which might be caused by the same error.
1. In case TCP_WRITE_FLAG_MORE is not always passed to tcp_write() (for the last portion of the buffer that is transmitted is not set) then the issue comes with a TCP Spurious Retransmission beside the 1s glitch.
2. In case the TCP_WRITE_FLAG_MORE is always passed to tcp_write() then the only symptom is the 1s stop.

Our TCP code is simple.
1. When data is available then send as many data as possible
using tcp_sendbuf() to learn the count then tcp_write() and then tcp_output().
2. From the TCP send callback do the same until all data is acked.
3. Send next buffer if data is available

I have attached two small pcap logs where the issue can be seen.

Can you please suggest a way how to track the issue?

Thank you in advance!

Peter Begella <begi>


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Attach Files:

Attached Files
file #51277:  tcp_1s_stop_after_window_update.pcapng added by begi (29KiB - application/octet-stream)


Depends on the following items: None found

Items that depend on this one: None found


Carbon-Copy List
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  • -email is unavailable- added by begi

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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2021-04-16 begi Attached File- => Added tcp_1s_stop_and_retransmission_after_window_update.pcapng, #51276
        Attached File- => Added tcp_1s_stop_after_window_update.pcapng, #51277
        Carbon-Copy- => Added begi

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