On Aug 11, 2010, at 12:34 PM, Terry Dontje wrote:
> I've done some minor testing on Linux looking at resident and shared
> memory sizes for np=4, 8 and 16 jobs. I could not see any
> appreciable differences in sizes in the process between sysv, posix
> or mmap usage in the SM btl.
> So I am still somewhat non-plussed about making this the default.
> It seems like the biggest gain out of using posix might be one
> doesn't need to worry about the location of the backing file. This
> seems kind of frivolous to me since there is a warning that happens
> if the backing file is not memory based.
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.
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.
> 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.
>> On Aug 11, 2010, at 10:05 AM, Graham, Richard L. wrote:
>>> Is this a modification of the existing component, or a new
>>> component ?
>>> On 8/10/10 10:52 AM, "Samuel K. Gutierrez" <samuel_at_[hidden]> wrote:
>>> I wanted to give everyone a heads-up about a new POSIX shared memory
>>> that has been in the works for a while now and is ready to be pushed
>>> into the
>>> Some highlights:
>>> o New posix component now the new default.
>>> o May address some of the shared memory performance issues
>>> when OMPI's session directories are inadvertently placed
>>> on a non-
>>> o Silent component failover.
>>> o In the default case, if the posix component fails
>>> 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
>>> and posix
>>> components (see: "System V Shared Memory for Open MPI: Request
>>> Input and Testing" thread).
>>> o Assuming local process homogeneity with respect to all utilized
>>> 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
>>> after the
>>> Tuesday morning conference call.
>>> Samuel K. Gutierrez
>>> Los Alamos National Laboratory
>>> devel mailing list
>>> devel mailing list
>> devel mailing list
> Terry D. Dontje | Principal Software Engineer
> Developer Tools Engineering | +1.650.633.7054
> Oracle - Performance Technologies
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