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

From: address@hidden
Subject: Re: [lwip-users] TCP retransmission flooding at end of stream
Date: Tue, 16 Sep 2014 21:10:20 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

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
- 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.


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