Task-Aware GASPI Library

The Task-Aware GASPI or TAGASPI library extends the functionality of the standard GASPI library by providing new mechanisms for improving the interoperability between parallel task-based programming models, such as OpenMP or OmpSs-2, and RDMA GASPI operations. The TAGASPI approach targets hybrid applications that taskify the RDMA communications. In this way, communication tasks can run in parallel, and also, they can overlap with computation tasks.

TAGASPI is currently compatible with the OmpSs-2 task-based programming model and the LLVM/OpenMP derivative implementation.

References

More information about this work can be found in the article below. Citations to the TAGASPI library should reference this article:

• Sala, K., Macia, S., & Beltran, V. (2021, September). Combining One-Sided Communications with Task-Based Programming Models. In 2021 IEEE International Conference on Cluster Computing (CLUSTER) (pp. 528-541). IEEE. [Article link]

Acknowledgments

This work was financially supported by the PRACE project funded in part by the EU’s Horizon 2020 Research programme (2014-2020) under grant agreement 823767.

Getting Started

This section describes the software requirements of TAGASPI, the building and installation process and how the library can be used from user applications.

Software Requirements

The Task-Aware GASPI library requires the installation of the following tools and libraries:

• Automake, autoconf, libtool, make and and C++ compiler supporting C++17.
• GPI-2 (tag tagaspi-2021.11) which extends the GASPI interface with the low-level operations API. We recommend configuring GPI-2 with MPI support in order to use mpirun or srun for launching hybrid applications. The GPI-2 version that supports the current TAGASPI version is the one included in the tag tagaspi-2021.11.
• Boost library version 1.59 or greater.
• One of the following parallel task-based programming models (required when compiling a user application):
  • OmpSs-2 (version 2023.11 or greater).
  • The derivative implementation of LLVM/OpenMP.

Building and Installing

TAGASPI uses the standard GNU automake and libtool toolchain. When cloning from a repository, the building environment must be prepared through the following command:

$ autoreconf -fiv

When the code is distributed through a tarball, it usually does not need that command.

Then execute the following commands:

$ ./configure --prefix=$INSTALLATION_PREFIX --with-gaspi=$GPI2_HOME --with-boost=$BOOST_HOME ..other options..
$ make
$ make install

where $INSTALLATION_PREFIX is the directory into which to install TAGASPI, $GPI2_HOME is the prefix of the extended GPI-2 installation, and $BOOST_HOME is the prefix of the Boost installation.

Other optional configuration flags are:

• --enable-debug-mode: Adds compiler debug flags and enables additional internal debugging mechanisms. Note that this flag can downgrade the overall performance. Debug mode is disabled by default.

Once TAGASPI is built and installed, e.g, in $TAGASPI_HOME, the installation folder will contain the libraries in $TAGASPI_HOME/lib (or $TAGASPI_HOME/lib64) and the headers in $TAGASPI_HOME/include. At this moment, TAGASPI is supporting C/C++ applications, but we are working on providing the Fortran support. The building procedure installs a single libtagaspi library (both in a dynamic and static format). There is a header file which can be included from user applications that declare all needed functions and constants: TAGASPI.h.

Run-time Options

The TAGASPI library has some run-time options that can be set through environment variables. These are:

• TAGASPI_POLLING_PERIOD (default 100 us): The polling period in microseconds in which the in-flight one-sided TAGASPI operations are checked by a transparent task in the background. This polling task is scheduled every specific number of microseconds to check the pending operations that have been issued by the tasks that called the TAGASPI communication services. This envar expects a positive integer number; the value 0 means that the task should be always running. Notice that the task leverages a CPU while running. By default, this task runs every 100 microseconds. This value may be decreased by the user in communication-intensive applications or increased in applications with low communication weights.

IMPORTANT: The TAGASPI_POLLING_FREQUENCY envar is deprecated and will be removed in future versions. Please use TAGASPI_POLLING_PERIOD instead. The deprecated envar is considered only when TAGASPI_POLLING_PERIOD is not defined.

Using TAGASPI in Hybrid Applications

User applications should be linked against the GPI-2 library, the OmpSs-2's runtime system and the TAGASPI library. Assuming that GPI-2 was built with MPI interoperability, a hybrid OmpSs-2+GASPI application can be compiled and linked as follows:

$ mpicxx -cxx=clang++ -fompss-2 -I$TAGASPI_HOME/include -I$GPI2_HOME/include app.cpp -o app.bin -ltagaspi -L$TAGASPI_HOME/lib -lGPI2 -L$GPI2_HOME/lib

Finally, the application binary can be launched as a regular GASPI/MPI program:

$ mpirun -n 4 ...binding options... ./app.bin

ALPI Tasking Interface

The Task-Aware GASPI library relies on the ALPI interface to communicate with the underlying tasking runtime system. This interface is internally used by TAGASPI to spawn internal tasks and add external events to user tasks that call TAGASPI functions. These lowlevel functionalities provide support for the TAGASPI asynchronous features.

The required interface is ALPI 1.0 (or any compatible) and it is included in the ALPI.hpp header. Any tasking runtime system can support this TAGASPI library by providing support to this interface version.