Re: [lwip-users] TCP retransmission flooding at end of stream

[address@hidden]

Michael Steinecke wrote:
> currently I'm struggling while creating an application for a custom
> STM32F429ZG based custom board using LwIP.
Too sad the F429 discovery board doesn't have an ethernet connector or I 
could try to reproduce this :-)
> To achieve maximum throughput, I have done some further, potential dangerous
> changes:
> - The MSS, TCP_SND_BUF, pbuf len, etc is increased from u16_t to u32_t. The
> MTU is still 1500. The problem with u16_t is the limitation the send buffer
> to a maximum of 0xFFFE bytes. For some checks in LwIP 0xFFFF is interpreted
> as 0x0000, but is need to have segments of 0xFFFF bytes for a fast
> processing of SD Card pages.

Which version of lwIP are you using? Do you know that we support TCP 
window scaling by now (LWIP_WND_SCALE)?

> - I decreased the TCP timer intervals from 250 ms to 10 ms. A even higher
> rate tends to produce a lot of retransmissions.
You should really not need to do this! I rather expect more problems 
than anything being solved. Especially when your main issue is sending 
data, not receiving.

I can't help you much on the rest, I'm afraid.


Simon