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From: lamaster@pioneer.arc.nasa.gov (Hugh LaMaster)
Newsgroups: comp.arch
Subject: Re: IBM RS6000
Message-ID: <1991Jan10.214122.9506@news.arc.nasa.gov>
Date: 10 Jan 91 21:41:22 GMT
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Reply-To: lamaster@pioneer.arc.nasa.gov (Hugh LaMaster)
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Scientific researchers are beginning to get results on the IBM RS6000 machines.
(Some RS6000's have apparently been shipping in quantity recently.)
I heard two comments today, which correspond with other things I have heard.
These comments are (beware, hearsay coming):

1)   The machines are as fast as other micros on scalar code, and a lot faster
     on vector code (other things being equal: clock speed, cache, etc. etc).
     Many of the codes here *are* vectorizable.

2)   The machine is very, very bad at context switches.  So bad, that response
     time becomes terrible with *one* CPU bound background process running.

Again, this is *hearsay*.  But, I am particularly curious if anyone has any
insight on 2) above.  Is it as bad as these various sources have reported?
Does anyone have any numbers on the cost of a context switch?  Is it a
function of process size, or ...whatever?

If it bad, why is it?  What is it about the design?  

Memory management?  

Cache?

O/S bug or feature?

How could IBM have missed something like this in the design (it should have
been obvious when the first prototype was built...?  Doesn't everyone do
big compiles as background jobs?)

Or, maybe this is just a smear campaign by IBM's rivals, who are upset that
IBM has an apparently hot product?

  Hugh LaMaster, M/S 233-9,  UUCP:                ames!lamaster
  NASA Ames Research Center  Internet:            lamaster@ames.arc.nasa.gov
  Moffett Field, CA 94035    With Good Mailer:    lamaster@george.arc.nasa.gov 
  Phone:  415/604-6117