Create an OpenCL Context using all CPU and GPU Devices - opencl

Question

I am using OpenCL 1.1. I am going to run my code on all of my gpus and all of my cpus. So, as the synchronization on two different contexts is hard to do, I wanted to create a context which contains all CPUs and GPUs as devices. So, First of all I am going to get all the platforms, then the devices related to each platform and then get CPU & GPU devices and store them in seperate vectors. Then afterward, to make the context I am going to create a vector made by all the CPU and GPU Devices. Then, I will call the clCreateContext. It will work fine but afterwards, when I want to create command queues for each device seprately, it always give me:
OpenCL call falls with error -34.
The code is as follows:
cl_int error = CL_SUCCESS;
cl_uint num_platforms;
clGetPlatformIDs(0, nullptr, &num_platforms);
if (num_platforms == 0){
std::cout << "Cannot find any platform.\n";
return;
}
platform.resize(num_platforms);
error = clGetPlatformIDs(num_platforms, platform.data(), nullptr);
checkError(error);
for (cl_uint i = 0; i < num_platforms; i++){
std::string platform_name;
size_t platform_name_len;
clGetPlatformInfo(platform[i], CL_PLATFORM_NAME, 0, nullptr, &platform_name_len);
platform_name.resize(platform_name_len);
clGetPlatformInfo(platform[i], CL_PLATFORM_NAME, platform_name_len, const_cast<char*>(platform_name.data()), nullptr);
std::cout << "[" << i << "]\t" << platform_name << std::endl;
std::vector<cl_device_id> devices(0);
cl_uint num_cpus = 0, num_gpus = 0;
error = clGetDeviceIDs(platform[i], CL_DEVICE_TYPE_CPU, 0, nullptr, &num_cpus);
error = clGetDeviceIDs(platform[i], CL_DEVICE_TYPE_GPU, 0, nullptr, &num_gpus);
devices.resize(num_cpus);
std::cout << "\tCPUS: \n";
error = clGetDeviceIDs(platform[i], CL_DEVICE_TYPE_CPU, num_cpus, devices.data(), nullptr);
for (cl_uint d = 0; d < num_cpus; d++){
std::string device_name;
size_t device_name_len;
clGetDeviceInfo(devices[d], CL_DEVICE_NAME, 0, nullptr, &device_name_len);
device_name.resize(device_name_len);
clGetDeviceInfo(devices[d], CL_DEVICE_NAME, device_name_len, const_cast<char*>(device_name.data()), nullptr);
std::cout << "\t\t[" << d << "]\t" << device_name << std::endl;
cpu_devices.push_back(devices[d]);
}
std::cout << "\tGPUS: \n";
devices.resize(num_gpus);
error = clGetDeviceIDs(platform[i], CL_DEVICE_TYPE_GPU, num_gpus, devices.data(), nullptr);
for (cl_uint d = 0; d < num_gpus; d++){
std::string device_name;
size_t device_name_len;
clGetDeviceInfo(devices[d], CL_DEVICE_NAME, 0, nullptr, &device_name_len);
device_name.resize(device_name_len);
clGetDeviceInfo(devices[d], CL_DEVICE_NAME, device_name_len, const_cast<char*>(device_name.data()), nullptr);
std::cout << "\t\t[" << d << "]\t" << device_name << std::endl;
gpu_devices.push_back(devices[d]);
}
}
std::vector<cl_device_id> devices;
for (size_t i = 0; i < cpu_devices.size(); i++)
devices.push_back(cpu_devices[i]);
for (size_t i = 0; i < gpu_devices.size(); i++)
devices.push_back(gpu_devices[i]);
ctx = clCreateContext(NULL, static_cast<cl_uint>(devices.size()), devices.data(), nullptr, nullptr, nullptr);
cpu_devices_queue.resize(cpu_devices.size());
for (size_t i = 0; i < cpu_devices.size(); i++){
cpu_devices_queue[i] = clCreateCommandQueue(ctx, cpu_devices[i], 0, &error);
checkError(error);
}
gpu_devices_queue.resize(gpu_devices.size());
for (size_t i = 0; i < gpu_devices.size(); i++){
gpu_devices_queue[i] = clCreateCommandQueue(ctx, gpu_devices[i], 0, &error);
checkError(error);
}

Answer 1

An OpenCL context can only encapsulate devices from a single platform, and cannot be created using devices from two or more different platforms.
You are not actually checking whether your call to clCreateContext succeeds. If you checked the return value or the error code, you would likely see that it was in fact failing. This is why when you later use that context in your call to clCreateCommandQueue, you receive error -34 (CL_INVALID_CONTEXT).