Getting Started

This page provides information on how to quickly get up and running with CHAI.

Installation

CHAI is hosted on GitHub here. To clone the repo into your local working space, type:

$ git clone --recursive [email protected]:LLNL/CHAI.git

The --recursive argument is required to ensure that the BLT submodule is also checked out. BLT is the build system we use for CHAI.

Building CHAI

CHAI uses CMake and BLT to handle builds. Make sure that you have a modern compiler loaded and the configuration is as simple as:

$ mkdir build && cd build
$ cmake -DCUDA_TOOLKIT_ROOT_DIR=/path/to/cuda ../

By default, CHAI will attempt to build with CUDA. CMake will provide output about which compiler is being used, and what version of CUDA was detected. Once CMake has completed, CHAI can be built with Make:

$ make

For more advanced configuration, see Configuring CHAI.

Basic Usage

Let’s take a quick tour through CHAI’s most important features. A complete listing you can compile is included at the bottom of the page. First, let’s create a new ManagedArray object. This is the interface through which you will want to access data:

chai::ManagedArray<double> a(100);

This creates a ManagedArray storing elements of type double, with 100 elements allocated in the CPU memory.

Next, let’s assign some data to this array. We’ll use CHAI’s forall helper function for this, since it interacts with the ArrayManager for us to ensure the data is in the appropriate ExecutionSpace:

forall(sequential(), 0, 100, [=] (int i) {
  a[i] = 3.14 * i;
});

CHAI’s ArrayManager can copy this array to another ExecutionSpace transparently. Let’s use the GPU to double the contents of this array:

forall(cuda(), 0, 100, [=] __device__ (int i) {
  a[i] = 2.0 * a[i];
});

We can access the array again on the CPU, and the ArrayManager will handle copying the modified data back:

forall(sequential(), 0, 100, [=] (int i) {
  std::cout << "a[" << i << "] = " << a[i] << std::endl;
});