Welcome to loopy’s documentation!

loopy is a code generator for array-based code in the OpenCL/CUDA execution model. Here’s a very simple example of how to double the entries of a vector using loopy:

import numpy as np
import loopy as lp
import pyopencl as cl
import pyopencl.array

# setup
# -----
ctx = cl.create_some_context()
queue = cl.CommandQueue(ctx)

n = 15 * 10**6
a = cl.array.arange(queue, n, dtype=np.float32)

# create
# ------
knl = lp.make_kernel(
        "{ [i]: 0<=i<n }",
        "out[i] = 2*a[i]")

# transform
# ---------
knl = lp.split_iname(knl, "i", 128, outer_tag="g.0", inner_tag="l.0")

# execute
# -------
evt, (out,) = knl(queue, a=a)

This example is included in the loopy distribution as examples/python/hello-loopy.py.

When you run this script, the following kernel is generated, compiled, and executed:

#define lid(N) ((int) get_local_id(N))
#define gid(N) ((int) get_group_id(N))

__kernel void __attribute__ ((reqd_work_group_size(128, 1, 1)))
  loopy_kernel(__global float *restrict out, __global float const *restrict a, int const n)
{

    if ((-1 + -128 * gid(0) + -1 * lid(0) + n) >= 0)
          out[lid(0) + gid(0) * 128] = 2.0f * a[lid(0) + gid(0) * 128];
}

(See the full example for how to print the generated code.)

Want to try out loopy?

There’s no need to go through Installation if you’d just like to get a feel for what loopy is. Instead, you may download a self-contained Linux binary. This is purposefully built on an ancient Linux distribution, so it should work on most versions of Linux that are currently out there.

Once you have the binary, do the following:

chmod +x ./loopy-centos6
./loopy-centos6 --target=opencl hello-loopy-lp.py
./loopy-centos6 --target=cuda hello-loopy-lp.py
./loopy-centos6 --target=ispc hello-loopy-lp.py

Grab the example here: examples/python/hello-loopy.py.

You may also donwload the most recent version by going to the list of builds, clicking on the newest one of type “CentOS binary”, clicking on “Browse” under “Build Artifacts”, then navigating to “build-helpers”, and downloading the binary from there.

Table of Contents

If you’re only just learning about loopy, consider the following paper on loo.py that may serve as a good introduction.

Please check Installation to get started.

Indices and tables