17.2. Open MPI v5.0.x series

This file contains all the NEWS updates for the Open MPI v5.0.x series, in reverse chronological order.

17.2.1. Open MPI version 5.0.0

Date:: 25 October 2023

The MPIR API has been removed

As was announced in the summer of 2017, Open MPI has removed support for MPIR-based tools beginning with the release of Open MPI v5.0.0.

Open MPI now uses the PRRTE runtime environment, which supports the PMIx tools API — instead of the legacy MPIR API — for debugging parallel jobs.

Users who still need legacy MPIR support should see https://github.com/hpc/mpir-to-pmix-guide for more information.

Zlib is suggested for better performance

PMIx will optionally use Zlib to compress large data streams. This may result in faster startup times and smaller memory footprints (compared to not using compression).

The Open MPI community recommends building PMIx with Zlib support, regardless of whether you are using an externally-installed PMIx or the bundled PMIx that is included with Open MPI distribution tarballs.

Note that while the Zlib library may be present on many systems by default, the Zlib header files — which are needed to build PMIx with Zlib support — may need to be installed separately before building PMIx.

Caution

Open MPI has changed the default behavior of how it builds and links against its required 3rd-party packages: Libevent, Hardware Locality, PMIx, and PRRTE.

Unlike previous versions of Open MPI, Open MPI 5.0 and later will prefer an external package that meets our version requirements, even if it is older than our internal version.
To simplify managing dependencies, any required packages that Open MPI v5.0.x bundles will be installed in Open MPI’s installation prefix, without name mangling.

For example, if a valid Libevent installation cannot be found and Open MPI therefore builds its bundled version, a libevent.so will be installed in Open MPI’s installation tree. This is different from previous releases, where Open MPI name-mangled the Libevent symbols and then statically pulled the library into libmpi.so.

Internal PMIx and PRRTe versions:
- PMIx release tag v4.2.7. Commit hash: 57c405c52ad76bab0be9f95e29a6df660673081e.
- PRRTE release tag v3.0.2. Commit hash: 1552e36f0852bbc6d901ec95983369f0a3c283f6.
All other notable updates for v5.0.0:
- MPI-4.0 updates and additions:
  - Support for MPI Sessions has been added.
  - Added partitioned communication using persistent sends and persistent receives.
  - Added persistent collectives to the MPI_ namespace (they were previously available via the MPIX_ prefix).
  - Added MPI_Isendrecv() and its variants.
  - Added support for MPI_Comm_idup_with_info().
  - Added support for MPI_Info_get_string().
  - Added support for initial_error_handler and the ERRORS_ABORT infrastructure.
  - Added error handling for unbound errors to MPI_COMM_SELF.
  - Made MPI_Comm_get_info(), MPI_File_get_info(), and MPI_Win_get_info() compliant to the standard.
  - Droped unknown/ignored info keys on communicators, files, and windows.
  - Initial implementations of MPI_COMM_TYPE_HW_GUIDED and MPI_COMM_TYPE_HW_GUIDED added.
  - MPI_Info_get() and MPI_Info_get_valuelen() are now deprecated.
  - Issue a deprecation warning when MPI_Cancel() is called for a non-blocking send request.
- New Features:
  - ULFM Fault Tolerance support has been added. See the ULFM section.
  - CUDA is now supported in the ofi MTL.
  - A threading framework has been added to allow building Open MPI with different threading libraries. It currently supports Argobots, Qthreads, and Pthreads. See the --with-threads option in the configure command. Thanks to Shintaro Iwasaki and Jan Ciesko for their contributions to this effort.
  - New Thread Local Storage API: Removes global visibility of TLS structures and allows for dynamic TLS handling.
  - Added new Accelerator framework. CUDA-specific code was replaced with a generic framework that standardizes various device features such as copies or pointer type detection. This allows for modularized implementation of various devices such as the newly introduced ROCm Accelerator component. The redesign also allows for Open MPI builds to be shipped with CUDA support enabled without requiring CUDA libraries.
  - Added load-linked, store-conditional atomics support for AArch64.
  - Added atomicity support to the ompio component.
  - osc/rdma: Added support for MPI minimum alignment key.
  - Add ability to detect patched memory to memory_patcher. Thanks to Rich Welch for the contribution.
  - coll/ucc: Added support for the MPI_Scatter() and MPI_Iscatter() collectives.
  - New algorithm for Allgather and Allgatherv has been added, based on the paper “Sparbit: a new logarithmic-cost and data locality-aware MPI Allgather algorithm”. Default algorithm selection rules are unchanged; to use these algorithms add: --mca coll_tuned_allgather_algorithm sparbit and/or --mca coll_tuned_allgatherv_algorithm sparbit to your mpirun command. Thanks to Wilton Jaciel Loch and Guilherme Koslovski for their contribution.
- Transport updates and improvements
  - One-sided Communication:
    - Many MPI one-sided and RDMA emulation fixes for the tcp BTL.
      
      This patch series fixs many issues when running with --mca osc rdma --mca btl tcp, i.e., TCP support for one sided MPI calls.
    - Many MPI one-sided fixes for the uct BTL.
    - Added support for acc_single_intrinsic to the one-sided ucx component.
    - Removed the legacy pt2pt one-sided component. Users should now utilize the rdma one-sided component instead. The rdma component will use BTL components — such as the TCP BTL — to effect one-sided communications.
  - Updated the tcp BTL to use graph solving for global interface matching between peers in order to improve MPI_Init() wireup performance.
  - OFI
    - Improved support for the HPE SS11 network.
    - Added cache bypass mechanism. This fixes conflicts with Libfabric, which has its own registration cache. This adds a bypass flag which can be used for providers known to have their own registration cache.
  - Shared Memory:
    - Update the new sm BTL to not use Linux Cross Memory Attach (CMA) in user namespaces.
    - Fixed a crash when using the new sm BTL when compiled with Linux Cross Memory Attach (XPMEM). Thanks to George Katevenis for reporting this issue.
  - Updated the -mca pml option to only accept one PML, not a list.
- Deprecations and removals:
  - The legacy sm (shared memory) BTL has been removed. The next-generation shared memory BTL vader replaces it, and has been renamed to be sm (vader will still work as an alias).
  - ORTE, the underlying Open MPI launcher has been removed, and replaced with the PMIx Reference RunTime Environment (PRTE).
  - PMI support has been removed from Open MPI; now only PMIx is supported. Thanks to Zach Osman for contributing.
  - The following components have been removed, and are replaced by UCX support: PML yalla, PML mxm, SPML ikrit.
  - The MTL psm component has been removed and is no longer supported.
  - Removed all vestiges of Checkpoint Restart (C/R) support.
  - 32 bit atomics are now only supported via C11 compliant compilers.
  - Explicitly disable support for GNU gcc < v4.8.1 (note: the default gcc compiler that is included in RHEL 7 is v4.8.5).
  - Various atomics support removed: S390/s390x, Sparc v9, ARMv4 and ARMv5 with CMA support.
  - The MPI C++ bindings have been removed.
  - The mpirun options --am and --amca options have been deprecated.
  - The libompitrace contributed library has been removed. This library was incomplete and unmaintained. If needed, it is available in the v4.x series.
  - The rankfile format no longer supports physical processor locations. Only logical processor locations are supported.
  - 32-bit builds have been disabled. Building Open MPI in a 32-bit environment is no longer supported. 32 bit support is still available in the v4.x series.
- Other updates and bug fixes:
  - Updated Open MPI to use ROMIO v3.4.1.
  - Add missing MPI_Status conversion subroutines: MPI_Status_c2f08(), MPI_Status_f082c(), MPI_Status_f082f(), MPI_Status_f2f08() and the PMPI_* related subroutines.
  - MPI module: added the mpi_f08 TYPE(MPI_*) types for Fortran. Thanks to George Katevenis for the report and their contribution to the patch.
  - The default atomics have been changed to be GCC, with C11 as a fallback. C11 atomics incurs sequential memory ordering, which in most cases is not desired.
  - Various datatype bugfixes and performance improvements.
  - Various pack/unpack bugfixes and performance improvements.
  - Various OSHMEM bugfixes and performance improvements.
  - Thanks to Jeff Hammond, Pak Lui, Felix Uhl, Naribayashi Akira, Julien Emmanuel, and Yaz Saito for their invaluable contributions.
- Documentation updates and improvements:
  - Open MPI has consolidated and converted all of its documentation to use ReStructured Text. and Sphinx.
    - The resulting documentation is now hosted on https://docs.open-mpi.org (via ReadTheDocs).
    - The documentation is also wholly available offline via Open MPI distribution tarballs, in the docs/_build/html directory.
  - Many, many people from the Open MPI community contributed to the overall documentation effort — not only those who are listed in the Git commit logs — including (but not limited to):
    - Lachlan Bell
    - Simon Byrne
    - Samuel Cho
    - Tony Curtis
    - Lisandro Dalcin
    - Sophia Fang
    - Rick Gleitz
    - Colton Kammes
    - Quincey Koziol
    - Robert Langfield
    - Nick Papior
    - Luz Paz
    - Alex Ross
    - Hao Tong
    - Mitchell Topaloglu
    - Siyu Wu
    - Fangcong Yin
    - Seth Zegelstein
    - Yixin Zhang
    - William Zhang