Date: Sun, 17 Feb 2002 16:13:03 -0800 (PST) From: Julian Elischer <julian@elischer.org> To: Terry Lambert <tlambert2@mindspring.com> Cc: Roy Sigurd Karlsbakk <roy@karlsbakk.net>, Dag-Erling Smorgrav <des@ofug.org>, Thomas Hurst <tom.hurst@clara.net>, hiten@uk.FreeBSD.org, hackers@FreeBSD.ORG, freebsd-questions@FreeBSD.ORG Subject: Re: in-kernel HTTP Server for FreeBSD? Message-ID: <Pine.BSF.4.21.0202171609260.39539-100000@InterJet.elischer.org> In-Reply-To: <3C703A92.2EBD3E67@mindspring.com>
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On Sun, 17 Feb 2002, Terry Lambert wrote: > > Fourth, I think the reason he made the joke about MSCE's > was that there are ways of doing true zero copy, using > DMA directly between devices. There are a couple of > people that have done this by, for example, rewriting > the Tigon II firmware to permit page aligned buffers, > and DMA'ing directly between disk and ethernet controllers. > > Technically, that's not zero copy, either, since there's > a copy on the disk, and one in some controller memory. > > "Zero copy" usually means "zero unnecessary copies"; but > what someone thinks of as "necessary" is really based on > their bias towards an existing implementation. At TFS we did this on BSD4.3, Mach 2.5 and FreeBSD(2.x) with proprietary protocols and proprieary network cards with lots of onboard RAM. We divided the RAM up into buffers and when we needed to send data we programmed the disk controllers to move the data directly to the network cards by DMA. This was on old slow busses but it gave us an order of magnitude advantage in bang per buck over the oposition.. Allowed us to do as much as them but on much cheaper hardware :-) Julian To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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