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

[John F. Haugh II]

In article <4616 at alvin.mcnc.org> spl at mcnc.org.UUCP (Steve Lamont) writes:
>A common criticism heard (and one that I made until I began working on
>interactive Crays some three years ago) is that you don't want to be running
>vi or emacs on a Cray.  The character level interrupts will kill the
>poor thing.  This is simply not true.  They simply do not happen
>frequently enough (from the machine's perspective) to worry about.

I have also heard that the overhead of sending single character I/O
requests over the hyperchannel was extremely costly.  The discussion
I've read claims that the amount of effort handling single character
at a time I/O [ like with Vi ] is too expensive in terms of CPU
cycles.

There is a posting in one of the sources groups which provides a Vi
frontend to ed running on a Cray.  I think it had a better description
of why Vi is a big loser on a supercomputer.

I was also going to disagree with Steve's remark vis memory
scheduling by pointing out that the machine has several hundred
megawords of physical memory.  I think that if you found the ratio
between computes [ in MIPS or MFLOPS ] and physical memory, you
might discover that compared to a 386PC with 8MB, a Cray is lacking
memory.  What do you think?
-- 
John F. Haugh II                        +-Button of the Week Club:-------------
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