Slide 14
Slide 14 text
Hello VexCL: vector sum
OpenCL
1 #include
2 #include
3 #include
4
5 #define __CL_ENABLE_EXCEPTIONS
6 #include
7
8 int main() {
9 // Get list of OpenCL platforms.
10 std::vector platform;
11 cl::Platform::get(&platform);
12
13 if (platform.empty())
14 throw std::runtime_error("No OpenCL platforms");
15
16 // Get first available GPU.
17 cl::Context context;
18 std::vector device;
19 for(auto p = platform.begin(); device.empty() && p != platform.end(); p++) {
20 std::vector pldev;
21 try {
22 p->getDevices(CL_DEVICE_TYPE_GPU, &pldev);
23 for(auto d = pldev.begin(); device.empty() && d != pldev.end(); d++) {
24 if (!d->getInfo()) continue;
25 device.push_back(*d);
26 context = cl::Context(device);
27 }
28 } catch(...) {
29 device.clear();
30 }
31 }
32 if (device.empty()) throw std::runtime_error("No GPUs");
33
34 // Create command queue.
35 cl::CommandQueue queue(context, device[0]);
36
37 // Prepare input data, transfer it to the device.
38 const size_t N = 1 << 20;
39 std::vector a(N, 1), b(N, 2), c(N);
40
41 cl::Buffer A(context, CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR,
42 a.size() * sizeof(float), a.data());
43
44 cl::Buffer B(context, CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR,
45 b.size() * sizeof(float), b.data());
46
47 cl::Buffer C(context, CL_MEM_READ_WRITE,
48 c.size() * sizeof(float));
49
50 // Create kernel source
51 const char source[] = R"(
52 kernel void add(
53 ulong n,
54 global const float *a,
55 global const float *b,
56 global float *c
57 )
58 {
59 ulong i = get_global_id(0);
60 if (i < n) c[i] = a[i] + b[i];
61 }
62 )";
63
64 // Compile OpenCL program for the device.
65 cl::Program program(context, cl::Program::Sources(
66 1, std::make_pair(source, strlen(source))
67 ));
68 try {
69 program.build(device);
70 } catch (const cl::Error&) {
71 std::cerr
72 << "OpenCL compilation error" << std::endl
73 << program.getBuildInfo(device[0])
74 << std::endl;
75 throw std::runtime_error("OpenCL build error");
76 }
77 cl::Kernel add(program, "add");
78
79 // Set kernel parameters.
80 add.setArg(0, static_cast(N));
81 add.setArg(1, A);
82 add.setArg(2, B);
83 add.setArg(3, C);
84
85 // Launch kernel on the compute device.
86 queue.enqueueNDRangeKernel(add, cl::NullRange, N, cl::NullRange);
87
88 // Get result back to host.
89 queue.enqueueReadBuffer(C, CL_TRUE, 0, c.size() * sizeof(float), c.data());
90 std::cout << c[42] << std::endl; // Should get '3' here.
91 }
VexCL
1 #include
2 #include
3 #include
4
5 int main() {
6 // Get first available GPU
7 vex::Context ctx(vex::Filter::GPU && vex::Filter::Count(1));
8 if (!ctx) throw std::runtime_error("No GPUs");
9
10 // Prepare and copy input data
11 const size_t n = 1024 * 1024;
12 std::vector a(n, 1), b(n, 2), c(n);
13 vex::vector A(ctx, a), B(ctx, b), C(ctx, n);
14
15 // Launch compute kernel
16 C = A + B;
17
18 // Get results back to host
19 vex::copy(C, c);
20 std::cout << c[42] << std::endl;
21 }