OpenMosix, opinions?

Ferdinand Mahr fmahr at gmx.de
Thu Oct 23 09:06:09 EDT 2003


Hi Leo,

> Imaging that we have an aplication. A pararell aplication that doesn't use a
> lot I/O operation, but intensive cpu, and some messages. Something like a
> pure parallel app. We implement it using PVM or MPI ... MPI. And we make a
> test, and we have some result.
> 
> Now, we have our beowulf, with a linux kernel with OpenMosix with a patch that
> can migrate threads (light weith process, Mighsm, http://mcaserta.com/maask/)
> or threads compiled with http://moss.csc.ncsu.edu/~mueller/pthreads/, that
> com from here: http://filibusta.crema.unimi.it/openmosix/fsu_threads_on_om/
> benchmark.htm.
> 
> We have our program, and we change it that use threads for the paralel
> behaviour and not MPI. And we run the same test. So, what will be better? Any
> one have tested it?

I haven't tested your special situation, but here are my thoughts about
it:

- Why changing an application that you already have? It costs you an
unnecessary amount of time and money.

- Migshm seems to enable OpenMosix to migrate System V shared memory
processes, not threads. But, "Threads created using the clone() system
call can also be migrated using Migshm", that's what you want, right? I
don't know how well that works, but it limits you to clone(), and I
don't know if thats sufficient for reasonable thread programming. Still
(as you mentioned before), you really can only write code that uses
minimum I/O and interprocess/thread communication because of network
limitations.

- Programs using PThreads don't run in parallel with OpenMosix/Migshm,
they can only be migrated in whole.

- If your MPI/PVM programs are well designed, they are usually really
fast and can scale very well when CPU-bound.

- Currently (Open)Mosix is better for load-balancing than HPC,
especially in clusters with different hardware configurations. In HPC
clusters, you usually have identical compute nodes.

Hope that helps,
Ferdinand
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