MSCP SCSI controller speed

[Paul Koning]

>>>>> "Allison" == Allison  <ajp166 at bellatlantic.net> writes:

 >> 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.

 Allison> You need a real time or single user os to get better
 Allison> results.  Plain old dos might do far better or maybe a
 Allison> custom kernal tuned for this use.

All you need is an application, or OS, that can queue up multiple
transfers.  I thought the buffered I/O in Unix would take care of
that.

Certainly if you do single I/Os and wait for the answer each time,
things will be slow, but the OS isn't really at fault then.

       paul