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Re: [lwip-users] TCP bandwidth limited by rate of ACKs

From: Bill Auerbach
Subject: Re: [lwip-users] TCP bandwidth limited by rate of ACKs
Date: Mon, 10 Oct 2011 11:31:11 -0400

>-----Original Message-----
>I was expecting to reach 80+ Mbit/s, so I captured the conversation
>with Wireshark, and I noticed that the sender is being throttled
>because the receiver (the STB running lwip) is not sending ACKs
>fast enough.
>cf. STB_TCP_RX_2.pcap (6 MB -- I truncated payloads to 100 bytes)
>(I've also attached a copy of my current lwipopts.h)
>Can someone nudge me in the right direction to optimize my
>build of lwip?

Some things are to optimize are the internet checksum, use zero-copy receive
and transmit, do SMEMCPY more efficiently, review/optimize memcpy, and use

Use LWIP_CHKSUM_ALGORITHM = 3 as it looks like it might be the best choice
for your processor.  Or better, code the checksum in assembly language.

If you can't use zero-copy receive and you have to copy the data, use a DMA
memory-to-memory copy if your hardware supports it.  The less you touch the
data the better.

Everything else I've done has been hardware dependent or used FPGA resources
(e.g. internet checksum).


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