On Apr 19, 2010, at 9:12 AM, Oliver Geisler wrote: > > >> Ah, that could do it. Open MPI's shared memory files are under /tmp. So if >> /tmp is NFS, you could get extremely high latencies because of dirty page >> writes out through NFS. >> >> You don't necessarily have to make /tmp disk-full -- if you just make OMPI's >> session directories go into a ramdisk instead of to NFS, that should also be >> sufficient. >> > > I just browsed FAQ and "ompi_info --param all all", but didn't find the > answer: > How do I set the OMPI session directory to point it to a ramdisk? >
Set the MCA param orte_tmpdir_base to point at the ramdisk using any of the MCA parameter methods (cmd line, envar, default mca param file). > And another question: > What would be a good size for the ram disk? One general value was > supposed by the FAQ with 128MB, but what is your experience? > (maybe a large topic by itself, so I have to try out, I guess) I don't recall the default shared memory size per process, but you can get that value from ompi_info --param btl sm. Take that value, multiply by your expected ppn, and then give yourself a fudge factor. > > Thanks a lot. > > Oli > > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. > > _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel
