JOHNSON%nuhub.acs.northeastern.edu@RELAY.CS.NET ("I am only an egg.") (09/22/86)
Help again. It has been brought to my
attention here that a user running a fixed job can
be charged varying amounts. Our charging
algorithm is simply rate/hour times CPU used.
This means that a user performing the same task
repeatedly with identical data is using differing
amounts of CPU resource. For our site, this is
not good.
Brent Sterner
Computing & Communications Services
Natural Sciences Building
The University of Western Ontario
London, Ontario, Canada
I've seen this too. There may be other things going on but one of
the big things going on is interrupt time. The last time I looked,
interrupt time was spread out over all users. It's very hard to figure
out who owns what interrupt time and charge for it. Hence the general
spreading of it over all jobs in the system. I've never timed it myself
but others have told me of changes of up to 20 percent plus between
stand-alone cpu time and busy interactive time for the same job. There
is no way I know of to separate this out in VMS. You might try a
weighted average but weighted against what?
I run into this kind of thing when faculty come to me wanting to
know how to time their algorithms for papers they are writing. I have
to explain to them that it can't be done meaningfully on an interactive
system. Of course they don't believe me and demand to know how other
people have timed their algorithms if not on an interative system. I
then explain about overhead and that the only meaningful cpu measurments
are made from a stand-alone system. I then direct them to my boss to
arrange for this. So far no one has gotten any stand-alone time. I
guess they're doing it at 2:00 am or something. It really gets painful
when computer science faculty ask this question. I get embarrassed.
US mail:
Chris Johnson
Academic Computer Services
Northeastern University 39RI
360 Huntington Ave.
Boston, MA. U.S.A. 02115
AT&T: (617) 437-2335
CSNET: johnson@northeastern.edu
ARPANET: johnson%northeastern.edu@relay.cs.net
"So what's reality anyway? Nothin' but a collective hunch."
Lily Tomlin