Date: Wed, 22 Mar 1995 02:40:17 -0800 (PST) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: bde@zeta.org.au (Bruce Evans) Cc: hasty@star-gate.com, phk@ref.tfs.com, faq@FreeBSD.org, hackers@FreeBSD.org Subject: Re: Why IDE is bad Message-ID: <199503221040.CAA08681@gndrsh.aac.dev.com> In-Reply-To: <199503221019.UAA09977@godzilla.zeta.org.au> from "Bruce Evans" at Mar 22, 95 08:19:58 pm
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> > >I don't think you will find many ide's faster than the WDC, I know > >it can run faster on a better IDE-controller, but this is a fairly > >standard IDE controller so it's a good indication. > >And yes, but FreeBSD doesn't support DMA in IDE (yet ?)... > > The WDC specs that I've seen show DMA speeds slightly slower than > IDE speeds so DMA may not be worth using. > > I forgot to think about the possibility of overlapping DMA cycles > with cpu cycles in my previous mail about this. I reported a 28% > slowdown for counting to 100000000. The cpu mostly executes 2 > instructions in a loop. There should be few bus accesses to slow > the cpu down. Maybe busmastering is broken. It may also be caused by the fact that your CPU has to run SNOOP cycles during the bus master DMA. I do not know if the 486 can run a SNOOP cycle at the same time it does a regular cache access, somehow I really doubt it. I do know that the Pentium can run SNOOPS and access both the instruction and the data caches all in the same cycle. Thats one heck of a lot of data moving all at once!!! > Bruce -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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