Date: Fri, 27 Feb 1998 10:11:46 -0800 (PST) From: Archie Cobbs <archie@whistle.com> To: mike@smith.net.au (Mike Smith) Cc: sthaug@nethelp.no, hackers@FreeBSD.ORG Subject: Re: "Best" Fast Ethernet Card Message-ID: <199802271811.KAA00364@bubba.whistle.com> In-Reply-To: <199802270509.VAA26266@dingo.cdrom.com> from Mike Smith at "Feb 26, 98 09:09:51 pm"
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Mike Smith writes: > > > > One *great* bonus is it will do IP, TCP and UDP checksums automagically > > > > in hardware! > > > > > > Oh great. This card was designed *explicitly* for Windows systems, > > > where they think it's funny for the network adapter driver to know > > > enough about the protocol layer to manage junk like this. > > > > Probably not. More likely it was simply meant to give lower CPU usage, > > given the right modifications to the TCP/IP stack. If you check the new > > Gigabit Ethernet cards that are becoming available, you'll find *most* > > of them will do IP checksum on-chip. > > It's odd then that these cards should be surfacing after NDIS 5 made > checksum calculations a feature of the NIC driver, no? > > > I've included below a recent Usenet article by Craig Partridge which > > explains some of the things that can be done to speed up BSD TCP/IP. > > You'll note that he explicitly mentions hardware checksums. > > Sure. However I think the point here is that you can only do hardware > checksums efficiently if you collapse the protocol stack to the point > where code has access to both the hardware and then TCP layer. > > That's expedient, and fast, but potentially *very* ugly. It also > raises the issue of fragment reassembly. There's nothing wrong with taking stable, existing, working code and optimizing it for the common case. For example, you could do it with an internal mbuf flag M_IPSUM that would indicate that the hardware has already verified the checksum on the packet. Sure it's not pretty, but it's a lot cleaner than some other stuff I've seen in there.. (the kernel, that is :-) -Archie ___________________________________________________________________________ Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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