9 Nov
2005
9 Nov
'05
4:22 p.m.
>>>> "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