Date: Mon, 3 Apr 1995 18:22:29 +1000 From: Bruce Evans <bde@zeta.org.au> To: davidg@Root.COM, luigi@labinfo.iet.unipi.it Cc: hackers@FreeBSD.org Subject: Re: NE2000 Plus performance Message-ID: <199504030822.SAA14278@godzilla.zeta.org.au>
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>1) how much faster are memory-mapped cards wrt io-mapped ones ? Is it > just the clock cycle per word that you save in transferring data > with MOVSW instead of INSW, or there is more (e.g. the driver That is about the only difference for mine. Much more than one clock cycle (at 8MHz) is saved. The memory mapped interface runs at about 3MB/sec while the i/o mapped interface runs at about 2MB/sec. Right now for an Addtron(?) AE-200JL in NE2000 mode on a 486DX2/66-VLB while running ttcp -r, systat reports the following overheads: 17.5%Sys 81.9%Intr 0.5%User 0.0%Nice 0.1%Idl i.e., the system is saturated. For the same setup except in WD8013EBT mode on a 486DX/33-ISA, the overheads are only 20.7%Sys 52.9%Intr 1.2%User 0.0%Nice 25.2%Idl This shows that NE2000 mode has more than 29% overhead for copying data from the ISA bus alone (the ISA bus is approximately equally slow for equivalent i/o's on the two machines). The interrupt overhead won't be much lower than 52.9% on faster (ISA) machines. I think wait states limit the MOVSW speed to 3.3MB/sec on my systems, so 1100K/sec for ethernet input must cost 33%. Bruce
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