Date: Sun, 21 Mar 1999 14:48:27 -0500 (EST) From: Alfred Perlstein <bright@rush.net> To: Terry Lambert <tlambert@primenet.com> Cc: Dag-Erling Smorgrav <des@flood.ping.uio.no>, andreas@klemm.gtn.com, rsnow@lgc.com, hasty@rah.star-gate.com, ckempf@enigami.com, wpaul@skynet.ctr.columbia.edu, freebsd-hackers@FreeBSD.ORG Subject: Re: Gigabit ethernet -- what am I doing wrong? Message-ID: <Pine.BSF.3.96.990321144541.4169H-100000@cygnus.rush.net> In-Reply-To: <199903211824.LAA13217@usr06.primenet.com>
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On Sun, 21 Mar 1999, Terry Lambert wrote: > > > AFAIK "zero copy tcp/ip" went into 3.1 and 4.0. Thanks to David > > > Greenman who implemented and tested this on ftp.cdrom.com. > > > (I hope I got the credits right ;-) > > > > No, that's only zero-copy transmission of files over stream sockets. > > OK, I'm real curious. > > How does this work? > > The lowest possible number of copiees I can consider is 1. This > assumes a DMA from the disk controller into the ethernet card > memory, and a cache-line unaligned one, at that, since the host > would have to pre-supply the packet header. That is zero copy, packet is DMA'd from card, then sent via DMA to another card, hence 0 copy. The CPU doesnt' have much work to do besides the DMA setups and a quick packet check, look at the fastforward code and you can see. -Alfred To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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