Date: 25 Feb 1997 08:27:50 +0000 From: Ashley Baumann <ashleyb@sco.com> To: "M. L. Dodson" <bdodson@beowulf.utmb.edu> Cc: freebsd-questions@freebsd.org Subject: Re: Adding memory slows down 486 to less than 386SX! Message-ID: <pxsybcdqohl.fsf@merlin.netlab.london.sco.com> In-Reply-To: "M. L. Dodson"'s message of Mon, 24 Feb 1997 15:28:01 -0600 References: <199702242128.PAA08444@beowulf.utmb.EDU>
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I know very little about FreeBSD internals, but could this be related to DMA?. My understanding is that ISA controllers can only DMA to memory < 16M. If FreeBSD does not guarantee that the disk buffers are below 16M the CPU has to do the work. This could account for the slowdown and the increased CPU utilisation. Just a thought Ashleyb "M. L. Dodson" <bdodson@beowulf.utmb.edu> writes: > Hello, > > I just upgraded a 486DX-25 from 8MB to 20MB memory and sequential > character disk I/O to a SCSI disk is now slower than to an IDE disk > on a 386SX! > ........ > > And why is CPU utilization so high for the block I/O on the 486 > relative to the 386SX? > > Any help would be appreciated. I'm at a loss. > > Bud Dodson
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