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From: spaf@cs.purdue.EDU (Gene Spafford)
Newsgroups: comp.sys.sequent
Subject: Re: I/O bottleneck?
Message-ID: <14947@ector.cs.purdue.edu>
Date: 6 Jun 91 13:38:28 GMT
References: <30721@hydra.gatech.EDU>
Sender: news@cs.purdue.EDU
Organization: Department of Computer Science, Purdue University
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Vincent notes that sometimes with 200+ people on, the CPU is 30%-40%
idle, and keyboard response is slow.  He concludes it is an I/O
problem.

That is very possibly correct, but i may not be the Ethernet as he
suggests.   Memory-starved machines behave the same way.  If the CPU
is spending a lot of time moving user pages in and out of memory,
processes will be blocked while awaiting their pages, and will not
appear to be using much of the CPU.  Vincent's attempt to type
something makes his job active and causes it to fight for the page
pool, too, thus giving the "jerky" behavior he notices.

Using "vmstat" to observe page faults would be a good idea.  It will
reveal if this is a problem or not.  The cure is not faster I/O, but
more memory.
-- 
Gene Spafford
NSF/Purdue/U of Florida  Software Engineering Research Center,
Dept. of Computer Sciences, Purdue University, W. Lafayette IN 47907-1398
Internet:  spaf@cs.purdue.edu	phone:  (317) 494-7825