SPEChpc™ 2021 Benchmark Description

621.miniswp_s (Minisweep)

Submitted by Wayne Joubert

Wayne Joubert

Scientific Computing

Oak Ridge National Laboratory

1 Bethel Valley Road
Oak Ridge, TN 37831

Bldg: 5600, Room: A321

Nuclear Engineering - Radiation Transport

The Minisweep proxy application is part of the Profugus radiation transport miniapp project that reproduces the computational pattern of the sweep kernel of the Denovo Sn radiation transport code. The sweep kernel is responsible for most of the computational expense (80-99%) of Denovo. Denovo, a production code for nuclear reactor neutronics modeling, is in use by a current DOE INCITE project to model the International Thermonuclear Experimental Reactor (ITER) fusion reactor. The many runs of this code required to perform reactor simulations at high node counts makes it an important target for efficient mapping to accelerated architectures.

Denovo was one of six applications selected for early application readiness on Oak Ridge National Laboratoryâ€™s Titan system under the Center for Accelerated Application Readiness (CAAR) project and is part of the Exnihilo code suite which received an R&D 100 award for modeling the Westinghouse AP1000 reactor. Minisweep can be considered a successor to the well-known Sweep3D benchmark and is similar to other Sn wavefront codes including Kripke, SN (Discrete Ordinates) Application Proxy (SNAP), and PARTISN.

MPI functions MPI_Isend, MPI_Irecv, along with a variety of variations of MPI_Bcast and MPI_Allreduce are used. The 3-dimensional space being modeled is partitioned into blocks whose size are configured at runtime via command line arguments. The resulting blocks are each bound to their own MPI rank.

Minisweep's input sizes are specified at runtime on the command line. It does not read in anything from an input file. Below is a list of command line options that can be used, as well as their corresponding descriptions taken from Minisweep's official documentation.

Additional information (including compilation/runtime examples)
can be found in Minisweep's github page at the link below:

https://github.com/wdj/minisweep/blob/master/doc/how_to_run.txt

--ncell_x The global number of gridcells along the X dimension. --ncell_y The global number of gridcells along the Y dimension. --ncell_z The global number of gridcells along the Z dimension. --ne The total number of energy groups. For realistic simulations may range from 1 (small) to 44 (normal) to hundreds (not typical). --na The number of angles for each octant direction. For realistic simulations a typical number would be up to 32 or more. NOTE: the number of moments is specified as a compile-time value, NM. Typical values are 1, 4, 16 and 36. NOTE: for CUDA builds, the angle and moment axes are always fully threaded. --niterations The number of sweep iterations to perform. A setting of 1 iteration is sufficient to demonstrate the performance characteristics of the code. --nproc_x Available for MPI builds. The number of MPI ranks used to decompose along the X dimension. --nproc_y Available for MPI builds. The number of MPI ranks used to decompose along the Y dimension. --nblock_z The number of sweep blocks used to tile the Z dimension. Currently must divide ncell_z exactly. Blocks along the Z dimension are kept on the same MPI rank. The algorithm is a wavefront algorithm, where every block is considered as a node of the wavefront grid for the wavefront calculation. NOTE: when nthread_octant==8, setting nblock_z such that nblock_z % 2 == 0 can considerably increase performance. --is_using_device Available for CUDA builds. Set to 1 to use the GPU, 0 for CPU-only (default). --is_face_comm_async For MPI builds, 1 to use asynchronous communication (default), 0 for synchronous only. --nthread_octant For OpenMP or CUDA builds, the number of threads deployed to octants. The total number of threads equals the product of all thread counts along problem axes. Can be 1, 2, 4 or 8. For OpenMP or CUDA builds, should be set to 8. Otherwise should be set to 1 (default). Currently uses a semiblock tiling method for threading octants, different from the production code. --nsemiblock An experimental tuning parameter. By default equals nthread_octant. --nthread_e For OpenMP or CUDA builds, the number of threads deployed to energy groups (default 1). The total number of threads equals the product of all thread counts along problem axes. --nthread_y For OpenMP or CUDA builds, the number of threads deployed to the Y axis within a sweep block (default 1). The total number of threads equals the product of all thread counts along problem axes. For CUDA builds, can be set to a small integer between 1 and 4. Not advised for OpenMP builds, as the parallelism is generally too fine-grained to give good performance. --nthread_z For OpenMP or CUDA builds, the number of threads deployed to the Z axis within a sweep block (default 1). The total number of threads equals the product of all thread counts along problem axes. Since the sweep block thickness in Z (ncell_z/nblock_z) commonly equals 1, this setting should generally be set to 1. Not advised for OpenMP builds, as the parallelism is generally too fine-grained to give good performance. --ncell_x_per_subblock For OpenMP or CUDA builds, a blocking factor for blocking the sweep block to deploy Y/Z threading. By default equals the number of cells along the X dimension for the given MPI rank, or half this amount if the axis is semiblocked due to octant threading. --ncell_y_per_subblock For OpenMP or CUDA builds, a blocking factor for blocking the sweep block to deploy Y/Z threading. By default equals the number of cells along the Y dimension for the given MPI rank, or half this amount if the axis is semiblocked due to octant threading. --ncell_z_per_subblock For OpenMP or CUDA builds, a blocking factor for blocking the sweep block to deploy Y/Z threading. By default equals the number of cells along the Z dimension for the given MPI rank, or half this amount if the axis is semiblocked due to octant threading. Since the sweep block thickness in Z (ncell_z/nblock_z) commonly equals 1, this setting should generally be set to 1.

Output values are summed for all octants and are stored in an array. Minisweep will print the contents of that array. Here is a partial example:

energy_totals[0]: 6016204800.000000 energy_totals[1]: 24064819200.000000 energy_totals[2]: 6016204800.000000 energy_totals[3]: 24064819200.000000 energy_totals[4]: 6016204800.000000 energy_totals[5]: 24064819200.000000 energy_totals[6]: 6016204800.000000 energy_totals[7]: 24064819200.000000 energy_totals[8]: 6016204800.000000 energy_totals[9]: 24064819200.000000 energy_totals[10]: 6016204800.000000

C

Last updated: July 16, 2018