kern/174851: [bxe] [patch] UDP checksum offload is wrong in bxe driver

[Barney Cordoba]

--- On Fri, 1/4/13, Willem Jan Withagen <wjw at digiware.nl> wrote:

> From: Willem Jan Withagen <wjw at digiware.nl>
> Subject: Re: kern/174851: [bxe] [patch] UDP checksum offload is wrong in bxe driver
> To: "Barney Cordoba" <barney_cordoba at yahoo.com>
> Cc: "Garrett Cooper" <yanegomi at gmail.com>, freebsd-net at freebsd.org, "Adrian Chadd" <adrian at freebsd.org>, "David Christensen" <davidch at freebsd.org>, linimon at freebsd.org
> Date: Friday, January 4, 2013, 9:41 AM
> 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

If you haven't benchmarked it, then you're just guessing. That's my point.

Its like SMP in freeBSD 4. People bought big, honking machines and the
big expensive machines were slower than a single core system at less than
half the price. Just because something sounds better doesn't mean that it is better.

BC