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Subject: Re: [OMPI devel] System V Shared Memory for Open MPI:Request forCommunity Input and Testing
From: Ashley Pittman (ashley_at_[hidden])
Date: 2010-05-04 10:32:25


On 4 May 2010, at 15:27, Jeff Squyres wrote:
> One thing to be careful with a run-time check is that you might not want *all* processes on a box to try to alloc a sysv segment, fork a child, try to connect, ...etc. With large count boxen, you might run out of sysv shmem segments if all procs try the test and/or run into OS serialization issues (someone here at the Forum cited a 96 core box). So you might want to have local rank 0 (or the orted? ...but that wouldn't work for srun / direct launch, etc.) do a test and communicate the results to the rest of the local procs -- maybe in the modex?

I think as as user I'd be quite surprised if my MPI job was spawning sub-processes during MPI_Init().

Ashley.

-- 
Ashley Pittman, Bath, UK.
Padb - A parallel job inspection tool for cluster computing
http://padb.pittman.org.uk