[rc5] Re: rc5-digest V1 #91

Sean McPherson sean at ntr.net
Thu Aug 21 10:29:14 EDT 1997

> When running SMP, the numbers do NOT scale exactly, for instance adding
> a second P233 would NOT double performace, at most it will increase by
> a factor of 1.5.  Adding a whole new machine, on the other hand, will
> more than double you processing speed for something like RC5, as it is
> sitting idle, not processing anything other than the client.
> ******************************
> Michael Chajkowski
> Desktop Technician
> StarField Productions
> email: mickyc at superiway.net
> ------------------------------

	What do you mean they don't scale? Depends on what OS you use.
Under linux, I'm definitely getting 2X performance. My Dual P200 runs 2
instances of RC5, and each one gets almost exactly the same amount of
keys/sec. The Dual P266 acts the same way, and hmm.... So do our SGI's.
Each CPU runs at 100% efficiency, if not more, as the system can run all
the system required processes on one CPU, and the other can do NOTHING but
rc5, when with 2 sep boxes, EACH hasta run it's own OS, hd access, etc.
Some OS's don't give a very good response on that second CPU, but some do!
Sure, there's a bit of overhead for acocunting and such, and I know you
then share disk IO/backplane/memory, etc, but that can have advantages as
well as the disadvantages.

Also, it seems I didn't explain some of what I said well enough about how
it depends on your situation. You mention having a second box that you can
give to someone else, and that runs RC5 faster total, by adding up the two
boxes' keys. But if you have a large databse on an OS writtent o take
advantage of multiple CPU's, such as Linux, and you write the DB software 
to be multi-CPU aware and threaded well, then a Quad CPU PPro might well
blow past your 2 boxes, as only one can be doing the request at one time!
The other one is a seperate box, and as such, can't help the performance
of the first one! I know that it can handle the NEXT request that comes
in, but one a per-request basis, it might not do as well.

	This wasn't a blatant attack on Non-Intel CPU's, people! My next
chip will prolly be a K6 233 for my NT server in my apartment, but for
businesses needing a lot of horsepower in ONE box, those just don't
necessarily do you any good! Sure, the Quad PPro or Dual PII-266 is
expensive, but if it works better than the AMD/Cyrix's and you HAVE to
have that performnace or lose data/business/time/money, it might be worth
it in the long run.

	Again, I'll close with saying IT DEPENDS ON WHAT YOU USE IT FOR.

Sean McPherson
sean at ntr.net
Systems Administration
NTR.Net Corporation
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