03-forloop

For loop exercise

Here, the purpose is to write a simple program using Kokkos that evaluates a loop from i = 0 to ì = 5. The loop calculates c[i] = a[i] * b[i] for all i on a GPU. Initialize the arrays a and b, eg, as follows:

for (unsigned i = 0; i < n; i++){
  a[i] = i;
  b[i] = 1;
}

At the end, the program should evaluate a verification loop (without Kokkos) to print out each c[i] to see the results are correct.

In addition to Kokkos::initialize() and Kokkos::finalize, you will need Kokkos::parallel_for and Kokkos::fence in this exercise. Furthermore, two different memory management strategies are investigated here:

Case 1: Raw pointers with Unified Memory

Kokkos::kokkos_malloc and Kokkos::kokkos_free are needed here.

Case 2: Views with explicit memory management

Kokkos::View and Kokkos::deep_copy are needed here.

Compiling and running

1. If not already done, enter directory /path/higher-level-gpu-programming/exercises/kokkos/ and clone kokkos by git clone https://github.com/kokkos/kokkos.git. Now the kokkos repo should be located in /path/higher-level-gpu-programming/exercises/kokkos/kokkos/ (you can use different location but this location is hardcoded in the solution Makefiles).

2. Then just create a source file and Makefile and type make. If you encounter compilation errors, make sure the backend compiler for the desired architecture is available, ie, nvcc for Mahti (use module load cuda) or hipcc for Lumi (use module load rocm). Hint! You can use the Makefile from the solution folder as a reference and just change the Kokkos path and the file name.

3. Run on Lumi or Mahti by srun ./executable (add required flags according to the underlying system and user, eg, --account=XXX, --partition=YYY, etc.)

Example solution

Example Kokkos implementations (.cpp) based on ENCCS material (CC-BY-4.0 license) are given in the solution folders. However, the intention is to try solving the exercise first without looking into these.