logo BabelStream is a benchmark used to measure the memory transfer rates to/from capacity memory. Unlike other memory bandwidth benchmarks this does not include any PCIe transfer time for attached devices. This benchmark is similar in spirit, and based on, the STREAM benchmark [1] for CPUs.

The choice of one programming model over another should ideally not limit the performance that can be achieved on a device. As such there are multiple implementations in a variety of programming models. Currently implemented are:

  • OpenCL
  • CUDA
  • OpenACC
  • OpenMP 3 and 4.5
  • Kokkos
  • RAJA
  • SYCL

As such this tool can be used as a kind of Rosetta Stone which provides both a cross-platform and cross-programming model array of results of achievable memory bandwidth.

[1]: McCalpin, John D., 1995: “Memory Bandwidth and Machine Balance in Current High Performance Computers”, IEEE Computer Society Technical Committee on Computer Architecture (TCCA) Newsletter, December 1995.


The source code is available on GitHub

Run rules

In order to generate a valid BabelStream result, you should obey the following rules:

  1. The array size must be large enough that increasing the array size does not drastically change the reported bandwidth. If you satisfy this you will no longer be affected by any cache effects.

  2. Each kernel should take a few milliseconds. The resolution of the host timer is probably in milliseconds so each kernel execution should be longer than the timer resolution. Increase the array size if the kernels are too fast. You are unlikely to break this rule if you follow rule 1.

If you see a single BabelStream result, expect this to be the largest bandwidth reported by the benchmark unless stated otherwise.