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mini-nbody: A simple N-body Code

A simple gravitational N-body simulation in less than 100 lines of C code, with CUDA optimizations.

Benchmarks

There are 5 different benchmarks provided for CUDA and MIC platforms.

  1. nbody-orig : the original, unoptimized simulation (also for CPU)
  2. nbody-soa : Conversion from array of structures (AOS) data layout to structure of arrays (SOA) data layout
  3. nbody-flush : Flush denormals to zero (no code changes, just a command line option)
  4. nbody-block : Cache blocking
  5. nbody-unroll / nbody-align : platform specific final optimizations (loop unrolling in CUDA, and data alignment on MIC)

Files

nbody.c : simple, unoptimized OpenMP C code timer.h : simple cross-OS timing code

Each directory below includes scripts for building and running a "shmoo" of five successive optimizations of the code over a range of data sizes from 1024 to 524,288 bodies.

cuda/ : folder containing CUDA optimized versions of the original C code (in order of performance on Tesla K20c GPU)

  1. nbody-orig.cu : a straight port of the code to CUDA (shmoo-cuda-nbody-orig.sh)
  2. nbody-soa.cu : conversion to structure of arrays (SOA) data layout (shmoo-cuda-nbody-soa.sh)
  3. nbody-soa.cu + ftz : Enable flush denorms to zero (shmoo-cuda-nbody-ftz.sh)
  4. nbody-block.cu : cache blocking in CUDA shared memory (shmoo-cuda-nbody-block.sh)
  5. nbody-unroll.cu : addition of "#pragma unroll" to inner loop (shmoo-cuda-nbody-unroll.sh)

mic/ : folder containing Intel Xeon Phi (MIC) optimized versions of the original C code (in order of performance on Xeon Phi 7110P)

  1. ../nbody-orig.cu : original code (shmoo-mic-nbody-orig.sh)
  2. nbody-soa.c : conversion to structure of arrays (SOA) data layout (shmoo-mic-nbody-soa.sh)
  3. nbody-soa.cu + ftz : Enable flush denorms to zero (shmoo-mic-nbody-ftz.sh)
  4. nbody-block.c : cache blocking via loop splitting (shmoo-mic-nbody-block.sh)
  5. nbody-align.c : aligned memory allocation and vector access (shmoo-mic-nbody-align.sh)