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[lwip-devel] [task #6849] Test how checksum on copy could be integrated

From: Simon Goldschmidt
Subject: [lwip-devel] [task #6849] Test how checksum on copy could be integrated into the stack
Date: Mon, 11 May 2009 16:09:10 +0000
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.4; de; rv: Gecko/2009042315 Firefox/3.0.10

Follow-up Comment #12, task #6849 (project lwip):

1) is done by telling lwIP to not care for creating/checking a specific
checksum (UDP, TCP, ICMP, IP). There are already defines for that.

2) would require a function tcp_enqueue_checksummed. I left that out in a
previous post but I would implement it just like udp_enqueue_checksummed.

Talking about efficiency: we can
a) let the application pre-calculate the checksum
b) create it when copying
c) create it in the driver

c) is obviously the best solution if the hardware supports on-the-fly
generation while copying the data using DMA. If not, it's not a good solution
at all!
Usage of a) and b) depend on the application: If you use TCP_NO_COPY or UDP
zero-copy (e.g. sockets), a) is of course better. If you copy anyway, the
overhead of an improved copy-and-checksum routine to a memcpy is minimal.

I'll try to create another patch for this to discuss about when I find the


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