[Beowulf] New HPCC results, and an MX question

Vincent Diepeveen diep at xs4all.nl
Wed Jul 20 19:31:34 EDT 2005


At 02:28 PM 7/20/2005 -0700, Greg Lindahl wrote:
>> Unless you want a very selected group to use your software, you'll have
>> to take care that multithreaded software also works fast for clusters.
>
>Vincent,
>
>Funny, in all my years of activity in the high performance computing
>niche, it's fairly rare that people run multi-threaded programs

It's the other way around.

MPI is so primitive that it doesn't allow multithreaded programs very well
and forces people to use a single process for calculations.

This is a severe handicap, as the average student is guessing that
multithreading is superior to multiprocessing.

You put it the other way around now.

You look in a tiny bottle and say: "it's all multiprocessing water".

Better is to look in the real world and see that there is much more water
in the ocean which could be all in your bottle.

Vincent

>accessing MPI. Pure MPI is the most widely used programming model,
>followed as a distant second by OpenMP programs where only the main
>thread does MPI (so a thread-safe MPI is not required), followed by a
>few, rare very codes which are multi-threaded with either OpenMP or
>Posix threads, and all the threads call MPI. Admittedly, this last
>choice is can be a good one if you have a multi-threaded program and
>want to add MPI. But there is a speed hit with low latency networks
>due to the extra locking needed. And that was the small point I was
>attemping to make.
>
>Perhaps you can point me at some huge existing market of threaded MPI
>programs? I'm sure you can speak with authority about your chess
>program, but I didn't realize you were an expert on the general MPI
>marketplace. With the advent of dual-core cpus, I figured the most
>likely future was that most people were going to continue to run their
>pure MPI programs as pure MPI programs.
>
>-- greg
>
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