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SYCL Academy

Exercise 18: Local Memory Tiling

In this exercise you will learn how to cache global memory into local memory in tiles according to work-groups in order to compare the performance difference.

1.) Use local memory

Allocate local memory for the kernel function by creating a local accessor.

The local accessor is created by specifying a range which is the number of elements to allocate.

Note that local memory is allocated per work-group and each work-group can only access it's own local memory.

2.) Cache global memory access in local memory

Cache the global memory required for each work-group in local memory by reading from global accessor and then writing to the local accessor.

Remember to use the local id to know where in local memory to store the data, this can be queried by calling the nd_item member function get_local_id.

Compare the performance with local memory and without local memory.

Build and execution hints

For DPC++: Using CMake to configure then build the exercise:

mkdir build
cd build
cmake .. "-GUnix Makefiles" -DSYCL_ACADEMY_USE_DPCPP=ON -DSYCL_ACADEMY_ENABLE_SOLUTIONS=OFF -DCMAKE_C_COMPILER=icx -DCMAKE_CXX_COMPILER=icpx
make exercise_18

Alternatively from a terminal at the command line:

icpx -fsycl -o sycl-ex-18 -I../External/Catch2/single_include ../Code_Exercises/Exercise_18_Local_Memory_Tiling/source.cpp
./sycl-ex-18

For AdaptiveCpp:

# <target specification> is a list of backends and devices to target, for example
# "omp;generic" compiles for CPUs with the OpenMP backend and GPUs using the generic single-pass compiler.
# The simplest target specification is "omp" which compiles for CPUs using the OpenMP backend.
cmake -DSYCL_ACADEMY_USE_ADAPTIVECPP=ON -DSYCL_ACADEMY_INSTALL_ROOT=/insert/path/to/adaptivecpp -DACPP_TARGETS="<target specification>" ..
make exercise_14

alternatively, without CMake:

cd Code_Exercises/Exercise_18_Local_Memory_Tiling
/path/to/adaptivecpp/bin/acpp -o sycl-ex-18 -I../../External/Catch2/single_include --acpp-targets="<target specification>" source.cpp
./sycl-ex-18