From owner-freebsd-hackers Wed Mar 22 02:42:13 1995 Return-Path: hackers-owner Received: (from majordom@localhost) by freefall.cdrom.com (8.6.10/8.6.6) id CAA00951 for hackers-outgoing; Wed, 22 Mar 1995 02:42:13 -0800 Received: from gndrsh.aac.dev.com (gndrsh.aac.dev.com [198.145.92.241]) by freefall.cdrom.com (8.6.10/8.6.6) with ESMTP id CAA00929; Wed, 22 Mar 1995 02:42:08 -0800 Received: (from rgrimes@localhost) by gndrsh.aac.dev.com (8.6.8/8.6.6) id CAA08681; Wed, 22 Mar 1995 02:40:17 -0800 From: "Rodney W. Grimes" Message-Id: <199503221040.CAA08681@gndrsh.aac.dev.com> Subject: Re: Why IDE is bad To: bde@zeta.org.au (Bruce Evans) Date: Wed, 22 Mar 1995 02:40:17 -0800 (PST) Cc: hasty@star-gate.com, phk@ref.tfs.com, faq@FreeBSD.org, hackers@FreeBSD.org In-Reply-To: <199503221019.UAA09977@godzilla.zeta.org.au> from "Bruce Evans" at Mar 22, 95 08:19:58 pm X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 1255 Sender: hackers-owner@FreeBSD.org Precedence: bulk > > >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