Hi folks,
WHAT:
Merge the htor-nbc branch to the trunk. This branch adds LibNBC support
to Open MPI (via compiler-wrappers mpi{cc,CC,xx,f90,...}-nbc.
WHY:
Users asked for it - this will enable to use non-blocking collective
operations with Open MPI easily.
WHEN:
Before 1.3 closes
TIMEOUT:
I will do the merge at February 13th if no one opposes.
DESCRIPTION:
LibNBC implements non-blocking collective operations in an MPI-style. It
was planned that Open MPI supports this extension as MPIX_<collective>.
However, this would require another MPIX_{Test,Wait} which might collide
with any MPIX_ extensions (cf. Generalized Requests). So we decided on
the Paris meeting last year that we just import LibNBC and keep the NBC_
namespace which should not collide with anything and enables portability
without code-changes (since LibNBC can be linked with any MPI).
More information on LibNBC is available in "Implementation and
Performance Analysis of Non-Blocking Collective Operations for MPI" and
on http://www.unixer.de/research/nbcoll/ .
Impact to the code base:
The impact will be minimal because LibNBC will be added as a third-party
library (like vt) in ompi/contrib/libnbc. Jeff did all the build-system
magic to get LibNBC's configure script called after ompi is built. So
this glue-code is also minimal.
Impact on compilation time:
The implementation will be compiled and installed by default (unless it
disables itself during configure).
Impact on running time:
No impact since it just offers additional functionality. No Open MPI
functionality will be changed. It is also only linked if those calls are
actually used. The command-line arguments are only added if the user
uses the -nbc mpi-compiler wrapper. However, using the calls does not
necessarily mean that the library achieves any overlap (this depends on
the network and also Open MPI's configuration, e.g., leave_pinned for
InfiniBand).
Best,
Torsten
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