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

[Willem Jan Withagen]

On 2013-01-05 16:17, Barney Cordoba wrote:
> 
> 
> --- 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.

I completely agree....

Dutch proverb goes:
	"To measure is to know"
Which was the subtitle of my graduation report, and my professional
motto when working as a systems-architect....

That's why it is sad that the system is no longer up and running,
because a 0-order check would be no more that 1 ifconfig would have made
a difference.

But that is all water under the bridge.

--WjW