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From: ken@harvard.edu (Ken Cleary)
Newsgroups: comp.arch
Subject: Re: IBM RS6000
Message-ID: <ken.663666109@nucleus>
Date: 12 Jan 91 07:41:49 GMT
References: <1991Jan10.214122.9506@news.arc.nasa.gov>
Sender: news@husc6.harvard.edu
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lamaster@pioneer.arc.nasa.gov (Hugh LaMaster) writes:

>Scientific researchers are beginning to get results on the IBM RS6000 machines.
>2)   The machine is very, very bad at context switches.  So bad, that response
>     time becomes terrible with *one* CPU bound background process running.

I did not do extensive benchmarking, but I tend to agree with the above.
I got only brief access to a demo machine, and I mostly just played with
the MIT X11 demo programs, like plaid, maze, etc.  As soon as I popped the 
first one up, I was amazed by the speed.  As I started running more copies of
these programs, I was surprised by the choppiness and slowdown of them.
I was not running more than 10 total copies of these rapidly animated graphics
demos.  (Yes, I realize that graphics updates may introduce I/O waits, so
perhaps this is not a fair benchmark, since a slow X terminal will take more
wall-clock time, for a graphically-animated client process, even though the
client won't be burning CPU cycles.)  Perhaps the choppiness is an indication
of course-grained time-slicing, so as to minimize context-switching?
{I may be stepping beyond the realms of my expertise, here.}