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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!news.mira.net.au!news.vbc.net!samba.rahul.net!rahul.net!a2i!bug.rahul.net!rahul.net!a2i!in-news.erinet.com!ddsw1!news.mcs.net!news.uoregon.edu!symiserver2.symantec.com!usenet From: tedm@agora.rdrop.com Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: 100BaseT tuning considerations? Date: 14 Sep 1996 17:11:45 GMT Organization: Symantec Corporation Lines: 41 Message-ID: <51ep0h$t3q@symiserver2.symantec.com> References: <4vin1s$4um@server.cs.vt.edu> <4vsr44$iom@hpindda.cup.hp.com> <514p1f$75h@nyx10.cs.du.edu> <DxKIq4.ICq@interactive.net> Reply-To: tedm@agora.rdrop.com NNTP-Posting-Host: 198.6.34.1 X-Newsreader: IBM NewsReader/2 v1.2.5 In <DxKIq4.ICq@interactive.net>, ritz@onyx.interactive.net (Chris Mauritz) writes: >Timothy Hu <thu@nyx10.cs.du.edu> wrote: >Or if you want a faster card with lower cpu utilization, get one >based on the DEC chipset (the SMC 10/100 cards come to mind). >Network Computing did a head to head test of the Intel/3COM/SMC Yes, their always doing NIC comparisons, that's their favorite thing to do. Unfortunately, they seem to think that only Novell Netware and NT exist as server operating systems. A NIC test on Novell has absolutely no relevance to FreeBSD. As far as the factors you ask about, there are basically 3 ways to get data out of core memory and into a bus peripheral card that are used by network adapters. First is IN/OUT instructions referred to as PIO mode, next is a "shared memory" scheme where the processor does a bunch or "rep mov" instructions to adapter card memory, last is some kind of DMA/Busmastering scheme where the CPU sets up a buffer in RAM and the card pulls the data out of memory. Unfortunately, it is not possible to make generalizations such as: "since busmastering requires lower CPU utilization than PIO mode, therefore card X which only does PIO is slower than card Y" simply because how these 3 schemes are implemented in hardware varies tremendously between card manufacturers, motherboards and quality of adapter components. You can the identical chipset used in different NICS from different manufacturers show different results, just because one manufacturer is saving a nickle per card by using a cheaper logic gate, for example. Also, how these schemes are implemented varies. You can have a PIO card take fewer instructions than a "shared memory" card simply because the shared memory card uses a brain-dead register set that takes tons more instructions to set up to make the transfer. Plus that, the device driver talking to the card varies tremendously. If you have a horribly written device driver on great hardware, it is going to be worse than a great device driver on mediocre hardware. Ted