9 Nov
2005
9 Nov
'05
12:27 p.m.
Subject: Re: MSCP SCSI controller speed
From: 9000 VAX <vax9000 at gmail.com>
Date: Wed, 09 Nov 2005 00:23:01 -0500
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
You are right. Those two are not the bottleneck. I measured the actual
execution time when run "dd if=syssrc.tar of=/dev/null" (photo
attached). NetBSD 1.5.2 moves 16kB a time. The measured time is:
4.75ms MSCP-pre-DMA overhead
0.4ms SCSI overhead
7ms DMA of 16kB
4.2ms MSCP-post-DMA overhead
31ms idle time
What kills the speed is the 31ms idle time. I blame NetBSD for that.
You need a real time or single user os to get better results. Plain old
dos might do far better or maybe a custom kernal tuned for this use.
nor wished to
program PCs. That and someone gave me a CMD SCSI adaptor. ;)
You are lucky. Nobody gives me CMD card. But from now on I probably
will not need one any more.