On May 4, 2010, at 9:32 AM, Ashley Pittman 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().
Point noted. But actually -- can you give specific reasons as to why a user should care? Keep in mind that this would be a short-lived fork'ed process -- not "spawn" in the MPI sense of the word. (I'm not advocating or refuting the idea -- I just want to understand why a user should care if the run-time system runs a quick test during startup) -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
