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To: "M. L. Dodson" <bdodson@beowulf.utmb.edu>
Cc: freebsd-questions@freebsd.org
Subject: Re: Adding memory slows down 486 to less than 386SX!
References: <199702242128.PAA08444@beowulf.utmb.EDU>
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From: Ashley Baumann <ashleyb@sco.com>
Date: 25 Feb 1997 08:27:50 +0000
In-Reply-To: "M. L. Dodson"'s message of Mon, 24 Feb 1997 15:28:01 -0600
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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