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From: hammond@faline.bellcore.com (Rich A. Hammond)
Newsgroups: comp.arch,comp.unix.wizards,comp.os.misc
Subject: Re: 98% in < 2s
Message-ID: <1411@faline.bellcore.com>
Date: Sat, 19-Sep-87 12:07:44 EDT
Article-I.D.: faline.1411
Posted: Sat Sep 19 12:07:44 1987
Date-Received: Sun, 20-Sep-87 15:39:58 EDT
References: <1665@ncr-sd.SanDiego.NCR.COM> <8579@utzoo.UUCP> <6886@eddie.MIT.EDU> <2473@xanth.UUCP>
Reply-To: hammond@faline.UUCP (Rich A. Hammond)
Organization: Bellcore MRE
Lines: 34
Xref: mnetor comp.arch:2250 comp.unix.wizards:4345 comp.os.misc:195

In article <> earl@mips.UUCP (Earl Killian) writes:
>In article <2473@xanth.UUCP>, kent@xanth.UUCP (Kent Paul Dolan) writes:
>
>> Second, another correspondent noted that in ten million process activations
>> on his system, 98% took less than two seconds of cpu time.  This means that
>> loading them was a significant fraction of all the work done in executing
>> them.

I'm skeptical about concluding that the processes took much work
to load.  The process activations are concentrated from 10AM to 6PM
with a dip around noon.  I'm willing to bet that the common commands
might have already been in main memory or buffer cache.

>It depends.  The realtime to vfork/exec something on my machine is ...

The relevant # is how long vfork takes on 11/780's, where the jobs ran.

>Also be careful not to assume that because 98% of the commands
>executed in < 2s that most of the work that a machine does is in such
>commands.  More complete data is necessary to make that conclusion as
>well.  The other 2% might execute for a long time...

Indeed they did, about 2/3 of 1% of the commands used up 66% of the CPU
resoures.  BUT, this # was cited in response to a question about improving
the UNIX filesystem performance because "A large proportion of all jobs
are I/O bound"  In fact, our observation is that a very few jobs used
up most of the CPU, and they did very little I/O per CPU hour.

I suspect this is still true today, although we have 8650's, Convex,
CCI, Pyramids and Alliants instead of 11/780's.  If I do a vmstat on
the Convex, I typically see: user 98% sys 2% idle 0%, hardly an I/O
bound situation.

Rich Hammond	hammond@bellcore.com