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Date: Fri, 04 Jan 2013 15:41:16 +0100
From: Willem Jan Withagen <wjw@digiware.nl>
Organization: Digiware Management b.v.
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To: Barney Cordoba <barney_cordoba@yahoo.com>
Subject: Re: kern/174851: [bxe] [patch] UDP checksum offload is wrong in bxe
 driver
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Cc: Garrett Cooper <yanegomi@gmail.com>, freebsd-net@freebsd.org,
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On 2013-01-01 0:04, Barney Cordoba wrote:

> The statement above "assumes" that there is a benefit. voIP packets 
> are short, so the benefit of offloading is reduced. There is some
> delay added by the hardware, and there are cpu cycles used in managing
> the offload code. So those operations not only muddy the code,
> but they may not be faster than simply doing the checksum on a much, much
> faster cpu.

Forgoing all the discussions on performance and possible penalties in
drivers.....

I think there is a large set of UDP streams (and growing) that do use
larger packets.

The video streaming we did used a size of header(14)+7*188, which is the
max number of MPEG packet to fit into anything with an MTU < 1500.

Receiving those on small embedded devices which can do HW check-summing
is very beneficial there.
On the large servers we would generate up to 5Gbit of outgoing streams.
I'm sure that offloading UDP checks would be an advantage as well.
(They did run mainly Linux, but FreeBSD would also work)

Unfortunately most of the infrastructure has been taken down, so it is
no longer possible to verify any of the assumptions.

--WjW