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From: dwc@homxc.UUCP (D.CHEN)
Newsgroups: comp.arch,comp.os.misc
Subject: Re: Unix File System Performance
Message-ID: <1350@homxc.UUCP>
Date: Mon, 21-Sep-87 16:43:29 EDT
Article-I.D.: homxc.1350
Posted: Mon Sep 21 16:43:29 1987
Date-Received: Wed, 23-Sep-87 02:14:11 EDT
References: <1384@faline.bellcore.com> <1397@faline.bellcore.com>
Organization: AT&T Bell Laboratories, Holmdel
Lines: 33
Xref: mnetor comp.arch:2285 comp.os.misc:207

> >>> Martin claimed a high proportion of jobs were I/O bound.
> >>I asked: ... Where do you get the idea that a high proportion are I/O bound?
> >>
> >From extensive workload analysis.  Try putting in a make.  Look at
> >your CPU utilization.  If its not 100%, you are waiting on I/O when you
> >could be processing.  Depending on how much you like to wait on I/O,
> >you are I/O bound.
> 
> This isn't realistic, given that disks have both a seek and rotational
> delay, the only way to get rid of ALL disk I/O time for a single job is
> to prefetch the data into main memory.  Only if you can predict what
> file I want before I ask for it can you have 100% CPU utilization.
> If you can do that, you can make a lot of money in the stock market. :-)

actually, from a bottleneck point of view, only SYSTEMs can be I/O
bound, not workloads.  although one job may always have i/o delay,
multiprocessing can allow the system to run without i/o delay.

> 
> I'll agree, those could benefit from more I/O bandwidth.  But do they
> need to be done under UNIX?  Wouldn't a dedicated OS to handle the
> disks and communications work better in the first case, even if the
> clients were UNIX systems?  Merging files might better be left to IBM MVS?
> As for shipping 32 M on all systems, this is a tradeoff between your
> development time and the incremental memory cost * # systems shipped.
> If you only ship a few systems and the 32 M solves the problem adequately,
> you'd be better off sticking it in.  Is the first one a real situation?
> 
why not do them under UNIX?  i'm sure that the other "special"
OSs must have also evolved under workload analysis.

danny chen
homxc!dwc