Tag: python

GPU kernel functions for deep learning

This article attempts to outline GPU Kernel Functions and how they are supported in TensorFlow, PyTorch, and OpenAI Triton. GPU Kernel Functions are specialized functions executed on an Nvidia Graphics Processing Unit. These functions play a key role in for parallel and accelerated computing such as tensor matrix operations used in deep learning.

GPU kernel functions for operations commonly used in deep learning include:

  1. Element-wise operations: TensorFlow provides GPU kernels for element-wise operations such as addition, subtraction, multiplication, and division, enabling efficient computation on arrays or tensors.
  2. Matrix operations: GPU kernels in TensorFlow optimize matrix operations like matrix multiplication, matrix addition, and matrix transpose, which are fundamental in many deep learning models.
  3. Convolutional operations: TensorFlow implements GPU kernels for convolutional operations, which are essential for tasks like image recognition and computer vision.
  4. Reduction operations: TensorFlow provides GPU kernels for reduction operations like summation, mean, maximum, and minimum, allowing efficient computation over large arrays or tensors.
  5. Activation functions: GPU kernels are implemented for common activation functions used in deep learning, such as ReLU (Rectified Linear Unit), sigmoid, and tanh.
  6. Pooling operations: TensorFlow’s GPU kernels optimize pooling operations like max pooling and average pooling, commonly used in convolutional neural networks (CNNs).
  7. Recurrent operations: TensorFlow provides GPU kernels for recurrent operations like LSTM (Long Short-Term Memory) and GRU (Gated Recurrent Unit), which are widely used in sequence-based models.

TensorFlow optimizes the execution of operations within a computation graph. When operations can be executed on a GPU, TensorFlow translates the high-level operations into CUDA calls that invoke the corresponding GPU kernels.

PyTorch is another popular open-source deep learning framework that provides a high-level programming interface for building and training machine learning models.

PyTorch differs from TensorFlow in a few ways:

  1. Dynamic Computational Graph: PyTorch uses a dynamic computational graph approach, whereas TensorFlow uses a static computational graph. This means that in PyTorch, the computational graph is constructed and executed on the fly as the code is executed, allowing for more flexibility and dynamic behavior during model training and inference.
  2. Imperative Programming: PyTorch follows an imperative programming style, which allows users to write code that is more intuitive and resembles standard Python programming. This makes it easier to understand and debug the code, as well as experiment with different model architectures and algorithms.
  3. Autograd: PyTorch’s autograd system allows automatic differentiation, which enables computing gradients for model parameters. This makes it easier to implement and train complex models, as users don’t have to manually compute gradients. TensorFlow, on the other hand, uses a static graph approach where gradients need to be explicitly defined and computed.
  4. TorchScript: PyTorch provides a feature called TorchScript, which allows models to be serialized and optimized for deployment in production environments. TorchScript enables efficient execution of PyTorch models on various platforms, including GPUs, CPUs, and mobile devices.

Like TensorFlow, PyTorch also implements GPU kernel functions for efficient computation on GPUs. It implements optimized GPU kernels similar to TensorFlow.

So while both TensorFlow and PyTorch provide GPU kernel function abstractions, their underlying computational graph models and programming styles differ, bringing their own unique advantages and trade-offs.

OpenAI Triton is a programming framework developed by OpenAI for building and deploying large-scale machine learning models efficiently. It leverages TensorFlow as its backend, supporting a wide range of models including deep learning and traditional algorithms. Triton offers tools for distributed computing, automated hyperparameter tuning, and model serving. It simplifies model deployment and management, making it suitable for both research and production environments. Triton abstracts away the need for users to write low-level GPU kernel functions by using TensorFlow’s optimized GPU operations implemented with CUDA, NVIDIA’s parallel computing platform. This approach allows developers to focus on defining high-level machine learning models without worrying about GPU optimization details.

It’s worth noting that Triton is built on top of TensorFlow, which supports alternative GPU acceleration libraries through backend integrations, and this enables Triton to leverage these alternatives to CUDA. One such alternative to CUDA is ROCm (Radeon Open Compute platform), developed by AMD. ROCm is an open-source GPU computing platform that provides support for AMD GPUs. TensorFlow has been working on integrating with ROCm, allowing it to utilize AMD GPUs for deep learning computations. As Triton relies on TensorFlow, it can benefit from this integration to support AMD GPUs through ROCm.

TorchScript for Model Optimization and Model Serving

TorchScript is an intermediate representation of a PyTorch model that can be optimized and run in a non-Python environment, making the PyTorch model suitable for deployment. It is part of the PyTorch ecosystem (Intro_to_TorchScript_tutorial.html , TorchScript JIT.html ).

Why is TorchScript needed ? Python while excellent for ML model development ( interpreted, REPL, simplicity, integration with number of ML libraries), also has characteristics that make it less suitable for model production deployments. These characteristics include interpretation overheads, complex dependency management, high memory/CPU overheads and the lack of easy integration with native technologies such as C++ for high performance and for embedded systems. TorchScript provides tools for optimizations such as operator fusion and static graph analysis which can improve the efficiency and performance during inference. Optimizing the models is crucial for embedded systems with limited resources.

PyTorch had introduced eager/dynamic execution, which had the advantage of faster user feedback but the disadvantage of not having as many optimizations as were possible in static approaches as in Tensorflow.

A blog on Key points to grasp about TorchScript – https://medium.com/@hihuaweizhu/key-points-to-grasp-for-torchscript-beginners-c02cf94aaa50, makes several good points, including that TorchScript is a subset of PyTorch and consists of statically typed variables.

A discussion between eager mode and script mode at https://towardsdatascience.com/pytorch-jit-and-torchscript-c2a77bac0fff suggests the benefit of TorchScript is more about dev/production (versus training/inference), with the production version requiring performance optimizations and portability. Quote: “With TorchScript, PyTorch aims to create a unified framework from research to production. TorchScript will take your PyTorch modules as input and convert them into a production-friendly format.

NVIDIA uses TorchScript to facilitate the deployment and optimization of PyTorch models within their ecosystem. The Torchscript models are compiled to TensorRT, the Nvidia runtime .

AWS ML software stack, Neuron, supports tracing in torchscript. https://awsdocs-neuron.readthedocs-hosted.com/en/latest/frameworks/torch/torch-neuronx/api-reference-guide/inference/api-torch-neuronx-trace.html . https://pytorch.org/docs/master/generated/torch.jit.trace.html#torch.jit.trace . An example of a neuron sdk trace for pytorch – https://github.com/aws-neuron/aws-neuron-sdk/issues/371 .

PyTorch/XLA is another project that integrates with Google XLA compiler to enable running PyTorch models on Google TPUs.

GraphCore produces hardware for deep learning called a GraphCore Intelligence Processing Unit (IPU). The primary software framework provided by GraphCore to execute machine learning models on their IPUs is Poplar. It allows running models from TensorFlow and PyTorch. Poplar optimizes computations for the unique architecture of GraphCore’s IPUs. This includes optimizations for memory bandwidth, parallel processing, and other hardware-specific features.