Cray I/O (was: Re: What kinds of things)

[Michael J. Tighe]

In article <873 at mtxinu.UUCP> shore at mtxinu.com (Melinda Shore) writes:
> Cray performance, at least on the Cray 1, the X-MP, and the Y-MP, is
> far more hampered by limited main memory.  Until fairly recently you
> couldn't get more than 8 megawords on an X and memory gets used up
> pretty quickly.
 
I am not so sure. I agree everybody wants more memory, but when each
of these machines came out (1/X/Y) the standard configuration came
with more memory than any other supercomputer (except the Cray-2)
available at that time. (there was a Cyber 205 that had 16 MW, but
that was a special case). A 16 MW X was available over 3 years ago.
Also they are constantly upgraded (X went from 4 MW to 64 MW, Y from
32 MW -> 128).
 
I think the real culprit is software. If you look at how much the
kernel (and utilities) have grown over the years, you will see where
all your memory has gone. By the time you get done with NFS, NQS, X11,
etc, there is no room left. I was reading the Standard C manual and it
said it needed 2 MW just to be built. Just a few years ago I booted
UNICOS on a 1 MW system. Now I can't even build a compiler on a 2 MW
system.
 
> At the same time, you probably want to avoid the use of an editor like
> GNU Emacs, which has a huge executable and apparently makes some
> obscene number of system calls per keystroke (Unicos isn't
> multithreaded yet).
 
Actually, the performance of GNU Emacs is not as bad as one might
think. You can lock it into a single CPU, and it can be compiled with
shared text. But this does not mean I believe you should turn your $25
million machine into a word processor.
 
> The best solutions are probably a distributed editor like rvi or NSF
> mounting your Cray directories on workstations and doing the editing
> there.
 
NFS seems to be a good choice, although it does have some security
problems. Also, by using Emacs and the function "compile-it" you can
execute your code on the Cray without ever leaving your editor or
logging on to the Cray.
-- 
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Michael Tighe
internet: mjt at super.org
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