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From: jbg@sei.cmu.edu (John Goodenough)
Newsgroups: comp.lang.ada
Subject: Re: Wanted: Performance Analysis Tools on PCs Info
Message-ID: <26009@as0c.sei.cmu.edu>
Date: 24 May 91 18:21:26 GMT
References: <1193@aviary.Stars.Reston.Unisys.COM>
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In-reply-to: gordon@Stars.Reston.Unisys.COM's message of 16 May 91 20:32:21 GMT
List-Id: <comp.lang.ada>


In article Wanted: Performance Analysis Tools on PCs Info of 16 May 91
20:32:21 GMT gordon@Stars.Reston.Unisys.COM (Del Gordon) writes:

>   There's a
>   project where Ada and PCs are required, and run-time performance
>   analysis is required to show that a given program does not use more
>   than a given percentage of the CPU or memory at any time.

Of course, if this is what your specification says you have to do, you have to
do it, but people should be aware that a measurement of overall CPU loading is
a very rough and sometimes quite misleading measure of how much extra capacity
is truly available in a system.  One of our case studies of the application of
rate monotonic analysis is of a system that was idle 46% of the time and was
not meeting its deadlines.  Rate monotonic analysis helped to show how to
restructure the system (by modifying a few hundred lines of application-level
code) so that all deadlines were met even though the system was still idle 46%
of the time.  (In essence, the restructuring of the code ensured that the
highest rate activity was not blocked very long by lower rate activities and
the rate monotonic analysis showed which blocking times needed to be reduced
and by how much.)  

A write-up of this case study might be available in a few months.  In the
meantime, to get a feeling for why gross measures of system load might be
misleading and to see some examples of better measures of available capacity
in a system, you might look at a paper by Steve Vestal in the Tri-Ada '90
Proceedings, although this won't help you to make the measurements your
project requires now.
John B. Goodenough					Goodenough@sei.cmu.edu
Software Engineering Institute				412-268-6391