Accelerating Python on GPUs with nvc++ and Cython

The C++ standard library contains a rich collection of containers, iterators, and algorithms that can be composed to produce elegant solutions to complex…

Ashwin Srinath
10 min readadvanced
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Overview

The article discusses how to accelerate Python code on GPUs using the nvc++ compiler and Cython. It provides practical examples, including sorting algorithms and the Jacobi method, demonstrating significant performance improvements over traditional NumPy implementations.

What You'll Learn

1

How to use Cython to call C++ functions from Python

2

How to implement GPU acceleration for C++ algorithms using nvc++

3

Why using stdpar can enhance performance of C++ algorithms

4

When to use local copies of data for GPU access in Cython

Prerequisites & Requirements

  • Basic understanding of C++ and Python programming
  • NVIDIA HPC SDK version 20.9 or higher

Key Questions Answered

How can I accelerate Python code using C++ algorithms?
You can use Cython to call C++ algorithms from Python, allowing you to leverage the performance of C++ standard library functions. By compiling with the nvc++ compiler and using the stdpar option, you can execute these algorithms on GPUs, significantly improving performance compared to traditional Python libraries like NumPy.
What performance improvements can I expect from using GPU acceleration?
The article demonstrates that GPU-accelerated C++ algorithms can perform approximately 20 times faster than NumPy's .sort method for larger problem sizes. This highlights the substantial performance gains achievable through GPU acceleration for compute-intensive tasks.
What are the limitations of using Cython with GPU acceleration?
One limitation is that input data must be copied into memory allocated by the C++ code compiled with nvc++. This means that data allocated by libraries like NumPy cannot be directly accessed by the GPU, requiring additional steps to manage memory effectively.
How do I build a Cython extension using nvc++?
To build a Cython extension with nvc++, you need to create a setup.py script that specifies the nvc++ compiler and includes necessary flags like -stdpar. This allows the extension to utilize GPU acceleration when executing algorithms.

Key Statistics & Figures

Performance improvement of GPU version over NumPy .sort
20x
This performance gain is observed for larger problem sizes when using the GPU-accelerated cppsort function.

Technologies & Tools

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Backend
Cython
Used to call C++ functions from Python and facilitate GPU acceleration.
Compiler
Nvc++
NVIDIA's C++ compiler used to compile code for GPU execution.
Library
Numpy
Used for array manipulation and as a baseline for performance comparison.

Key Actionable Insights

1
Leverage Cython to bridge Python and C++ for performance-critical applications.
Using Cython allows Python developers to access the speed of C++ algorithms without extensive C++ knowledge, making it easier to optimize existing Python code.
2
Consider GPU acceleration for large-scale data processing tasks.
For applications that involve heavy computation, such as sorting large datasets or solving numerical methods, offloading tasks to the GPU can yield significant performance improvements.
3
Always manage memory carefully when using GPU acceleration.
Since the GPU can only access memory allocated in the context of the C++ code, ensure that data is copied appropriately to avoid performance bottlenecks.

Common Pitfalls

1
Failing to copy input data into a format accessible by the GPU can lead to errors.
This occurs because the GPU cannot access memory allocated by Python libraries like NumPy, requiring developers to manage data allocation explicitly.

Related Concepts

Cython
GPU Programming
C++ Standard Library Algorithms
Performance Optimization Techniques