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Neural Network Evaluation Parallelization
Neural networks work by activating neurons in the prior row based on the linear combination of the prior row and weights determined by the network's training.
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Matrix operations are easily parallelized. Below is a table showing the number of operations needed to multiply an NxN matrix by a vector of length N, the number of cycles needed if optimally parallelized, and the number of cores to achieve optimal parallelization.
| N | Operations | Parallelized Cycles | Cores Required |
|---|---|---|---|
| 2 | 6 | 2 | 4 |
| 4 | 28 | 3 | 16 |
| 8 | 120 | 4 | 64 |
| 16 | 496 | 5 | 256 |
| 32 | 2,016 | 6 | 1,024 |
| 64 | 8,128 | 7 | 4,096 |
| 128 | 32,640 | 8 | 16,384 |
Commercial CPUs top out at around 32 cores (AMD Ryzen Threadripper 3970X), so for anything more complex than 5x5 matrices, we need to use GPUs, which have more cores.
GPUs
GPUs have many more cores than any CPU. Although they cannot handle processes as complex as CPUs, they are great at performing simple addition and multiplication very quickly.
GPUs also have the advantage of specially designed circuits to do addition and multiplication in a single clock cycle (GPUs can take several). They can also have circuits specifically designed to do matrix multiplication, able to multiply two 4x4 matrices in a single clock cycle.
For more information on GPUs, see Cornell, and NVIDIA.
On the computer used for training, we are using an RTX A4000. Its full datasheet can be found here.
ONNX
ONNX
ONNX (The Open Neural Network Exchange) is an AI ecosystem that created standards for representing machine learning algorithms. These standards allow ONNX machine learning algorithms to be run on a wide variety of machines (unfortunately excluding Apple).
ONNX supports a wide variety of frameworks, including Matlab, Keras, TensorFlow, and PyTorch. For a full list and detailed instructions on converting to and from ONNX models, see this page: https://onnx.ai/supported-tools.html
Instructions for converting a TensorFlow model to ONNX:
- Install ONNX convertor:
pip install git+https://github.com/onnx/tensorflow-onnx - To convert a model from TensorFlow to ONNX, run the following.
python -m tf2onnx.convert --saved-model tensorflow-model-path --output model.onnx - The model is now ready to be run on ONNX Runtime.
ONNX Runtime
ONNX does not itself perform inference. To do that, you need to install a runtime that can run ONNX. Use the following website for installation and operation instructions: https://onnxruntime.ai/index.html#getStartedTable
Using this, you can perform inference up to 17x faster. ONNX Runtime also allows you to accelerate PyTorch training (only PyTorch so far) up to 40% faster.