Samuel K. Gutierrez wrote:

If I'm not mistaken, the warning is only issued if the backing files is stored on the following file systems: Lustre, NFS, Panasas, and GPFS  (see: opal_path_nfs in opal/util/path.c).  Based on the performance numbers that Sylvain provided on June 9th of this year (see attached),  there was a performance difference between mmap on /tmp and mmap on a tmpfs-like file system (/dev/shm in that particular case).  Using the new POSIX component provides us with a portable way to provide similar shared memory performance gains without having to worry about where the OMPI session directory is rooted.

Is there not a way to determine whether the fs is tmpfs or not?  It seems fixing that is a lot  less changes then adapting to Posix shared memory.  My main concern is we have had quite a long runtime with the mmap implementation and know it works for us.  We haven't had nearly as much runtime with this Posix implementation and so who knows what issues we might run into.  Note, I am not saying Posix is broken I am just saying we have not used it within our btl as much and who knows what we might run into (or not).

To me the fs homing issue seems like a weak case.  I understand it is an out of the box feature and nicety but I just wonder if that weakness is better solved without replacing the shared memory calls we use.  Note, I am on the fence to some extent on this.  I understand that we could give this feature a lot of soak time and probably come to a reasonable belief we haven't gone backwards somehow but it just seems like there is very little gain in this IMO.

Am I in the minority on the above belief?

--td

--
Samuel K. Gutierrez
Los Alamos National Laboratory 



I still working on testing the code on Solaris but I don't imagine I will see anything that will change my mind.

--td

Samuel K. Gutierrez wrote:
Hi Rich,

It's a modification to the existing common sm component.  The modifications do include the addition of a new POSIX shared memory facility, however.

Sam

On Aug 11, 2010, at 10:05 AM, Graham, Richard L. wrote:

Is this a modification of the existing component, or a new component ?

Rich


On 8/10/10 10:52 AM, "Samuel K. Gutierrez" <samuel@lanl.gov> wrote:

Hi,

I wanted to give everyone a heads-up about a new POSIX shared memory
component
that has been in the works for a while now and is ready to be pushed
into the
trunk.

http://bitbucket.org/samuelkgutierrez/ompi_posix_sm_new

Some highlights:
o New posix component now the new default.
       o May address some of the shared memory performance issues users
encounter
          when OMPI's session directories are inadvertently placed on a non-
local
          filesystem.
o Silent component failover.
       o In the default case, if the posix component fails initialization,
          mmap will be selected.
o The sysv component will only be queried for selection if it is
placed before
   the mmap component (for example, -mca mpi_common_sm
sysv,posix,mmap).  In the
   default case, sysv will never be queried/selected.
o Per some on-list discussion, now unlinking mmaped file in both mmap
and posix
   components (see: "System V Shared Memory for Open MPI: Request for
Community
   Input and Testing" thread).
o  Assuming local process homogeneity with respect to all utilized
shared
    memory facilities. That is, if one local process deems a
particular shared
    memory facility acceptable, then ALL local processes should be
able to
    utilize that facility. As it stands, this is an important point
because one
    process dictates to all other local processes which common sm
component will
    be selected based on its own, local run-time test.
o Addressed some of George's code reuse concerns.

If there are no major objections by August 17th, I'll commit the code
after the
Tuesday morning conference call.

Thanks!

--
Samuel K. Gutierrez
Los Alamos National Laboratory





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Developer Tools Engineering | +1.650.633.7054
Oracle - Performance Technologies
95 Network Drive, Burlington, MA 01803
Email terry.dontje@oracle.com