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SYCL Academy

Exercise 16: Coalesced Global Memory

In this exercise you will learn how to apply row-major and column-major when linearizing the global id in order to compare the performance difference due to coalesced global memory access.

1.) Evaluate global memory access

Now that you have a working grayscaling kernel you should evaluate whether the global memory access patterns in your kernel are coalesced.

Consider two alternative ways to linearize the global id:

auto rowMajorLinearId    = (idx[1] * width) + idx[0];  // row-major
auto columnMajorLinearId = (idx[0] * height) + idx[1];  // column-major

Try using both of these and compare the execution time of each.

Build and execution hints

ComputeCpp:

cmake -DSYCL_ACADEMY_USE_COMPUTECPP=ON -DSYCL_IMPLEMENTATION_INSTALL_ROOT=/insert/path/to/computecpp ..
make exercise_16_coalesced_global_memory_source
./Code_Exercises/Exercise_16_Coalesced_Global_Memory/exercise_16_coalesced_global_memory_source

DPC++:

icpx -fsycl -I../../External/Catch2/single_include -I../../Utilities/include/ -I../../External/stb solution.cpp