Date: Mon, 07 Jan 2013 09:20:40 +0100 From: Willem Jan Withagen <wjw@digiware.nl> To: Barney Cordoba <barney_cordoba@yahoo.com> Cc: Garrett Cooper <yanegomi@gmail.com>, freebsd-net@freebsd.org, Adrian Chadd <adrian@freebsd.org>, David Christensen <davidch@freebsd.org>, linimon@freebsd.org Subject: Re: kern/174851: [bxe] [patch] UDP checksum offload is wrong in bxe driver Message-ID: <50EA8558.4010600@digiware.nl> In-Reply-To: <1357399030.5935.YahooMailClassic@web121603.mail.ne1.yahoo.com> References: <1357399030.5935.YahooMailClassic@web121603.mail.ne1.yahoo.com>
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On 2013-01-05 16:17, Barney Cordoba wrote: > > > --- On Fri, 1/4/13, Willem Jan Withagen <wjw@digiware.nl> wrote: > >> From: Willem Jan Withagen <wjw@digiware.nl> >> Subject: Re: kern/174851: [bxe] [patch] UDP checksum offload is wrong in bxe driver >> To: "Barney Cordoba" <barney_cordoba@yahoo.com> >> Cc: "Garrett Cooper" <yanegomi@gmail.com>, freebsd-net@freebsd.org, "Adrian Chadd" <adrian@freebsd.org>, "David Christensen" <davidch@freebsd.org>, linimon@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
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