C[omp]ute

From: andrew cooke <andrew@...>

Date: Fri, 30 Sep 2011 17:42:26 -0300

I'm finding pyopencl to be both very cool (so much less code to write) and
very frustrating (such crappy documentation).  So here are some completely
basic examples that might help others:

Andrew


def test1():
    '''you might think the Array class is something that simplifies code.
       this example shows it is not (change the comments and see the errors).
       instead, it seems to be something that looks like a numpy array,
       but which farms out work to the GPU (operation by operation).'''
    
    ctx = cl.create_some_context()
    queue = cl.CommandQueue(ctx)

    a = n.array([0], dtype=n.int32)

    # this works
    a_dev = cl.Buffer(ctx, cl.mem_flags.WRITE_ONLY, a.nbytes)
    # this alternative (plus below) fails
    #a_dev = cla.to_device(queue, a)

    prg = cl.Program(ctx, """
        __kernel void test1(__global int* a) {
            a[0] = 1;
        }
        """).build()

    event = prg.test1(queue, (1,), None, a_dev)
    event.wait()

    # this works
    cl.enqueue_copy(queue, a, a_dev)
    # this alternative(plus above) fails
    #a = a_dev.get()
    
    print(a)


def test3():
    '''constants (like b) don't need buffering.'''
    
    ctx = cl.create_some_context()
    queue = cl.CommandQueue(ctx)

    a = n.array([0], dtype=n.int32)
    b = n.int32(4)

    a_dev = cl.Buffer(ctx, cl.mem_flags.WRITE_ONLY, a.nbytes)

    prg = cl.Program(ctx, """
        __kernel void test1(__global int* a, const int b) {
            a[0] = b;
        }
        """).build()

    event = prg.test1(queue, (1,), None, a_dev, b)
    event.wait()

    cl.enqueue_copy(queue, a, a_dev)

    print(a)