Awesome Open Source
Awesome Open Source

Dot product benchmark

*Author: Tobit Flatscher (December 2019)


These are several cache-optimised implementations of the simple dot product of two vectors. The dot product is calculated in parallel using multi-threading with OpenMP and vectorisation either with OpenMP or manually with AVX2 or AVX512 intrinsics. Additionally the code makes use of templating, cache-aligned arrays (with Boost for vectors if available) and compile-time constexpr functions. The different implementations are benchmarked against each other to check how well the compilers deal with auto-vectorisation for such a simple case. Ideally the compiler should perform similarly to the manual intrinsics. While this seems to be the case with the Intel compiler, GCC struggles to achieve the same performance. Interestingly vectors do not seem to be fully cache-line aligned by both compilers even with optimisation flags such as -O3.

The files

  • bin/ Folder for compiled binaries (created by Makefile)
  • obj/ Folder for object files (created by Makefile)
  • src/ Folder for source and header files
  • Makefile The Make-file (default GCC) and settings for the ICC and GCC compiler
  • vec_vs_arr.cbp CodeBlocks project files
  • bin/main.GCC The executable compiled with GCC
  • bin/main.ICC The executable compiled with ICC
  • src/align.hpp Defines the cache-line-alignment relevant C++ macros (call to a Boost-vector if available)
  • src/avx2_omp.hpp Implementation of dot-product by means of manual AVX2 intrinsics and multi-threading with OpenMP
  • src/avx512_omp.hpp Implementation of dot-product by means of manual AVX512 intrinsics and multi-threading with OpenMP
  • src/avx_omp.hpp Determine which version of AVX is available
  • src/benchmark.hpp Generic functions for benchmarking
  • src/constexpr_func.hpp The implementation of a square root with the recursive Newton-Raphson method that can be evaluated to constant expression at compile time
  • src/disclaimer.hpp Prints out a disclaimer and tries to identify operating, compiler and features at compile time
  • src/init.hpp Initialises vectors and arrays with random numbers
  • src/main.cpp The main-file of this program
  • src/omp_simd.hpp Implementation of dot-product by means of auto-vectorisation and multi-threading with OpenMP
  • src/span.hpp std::span-like container by Tristan Brindle that will be introduced in C++20
  • src/timer.hpp A simple wrapper for the chrono-library timer

Launch it

Copy this folder or directly clone this repository by typing

$ git clone 

Make sure if the Intel compiler collection is installed on your system by opening a console and typing

$ icc -v

If it is not available on your system install it (it is free of charge for students) and change the corresponding lines of the Make-file Makefile

1  # Makefile
2  # Tobit Flatscher - (2020)
4  # Compiler settings (alternatively: export COMPILER=)

else you can leave it on GCC and use the Gnu Compiler Collection only. Finally compile it by typing

$ make clean
$ make run

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