# Speed up inference of forecaster through ONNXRuntime#

## Introduction#

In the inferencing process, it is desirable to speed up. One way to do this is to utilize some accelerators, such as ONNXRuntime.

Actually, utilizing ONNXRuntime to accelerate is easy in Chronos, that is directly calling predict_with_onnx (optionally build_onnx). In this guidance, we demonstrate how to speed up inference of forecaster through ONNXRuntime in detail.

We will take TCNForecaster and nyc_taxi dataset as an example in this guide.

## Setup#

Before we begin, we need to install chronos if it isn’t already available, we choose to use pytorch as deep learning backend.

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!pip install --pre --upgrade bigdl-chronos[pytorch]
# install ONNXRuntime
!pip install onnx
!pip install onnxruntime
# uninstall torchtext to avoid version conflict
!pip uninstall -y torchtext


📝Note

• Although Chronos supports inferencing on a cluster, the method to speed up can only be used when forecaster is a non-distributed version.

• Only pytorch backend deep learning forecasters support onnxruntime acceleration.

## Forecaster preparation#

Before the inferencing process, a forecaster should be created and trained. The training process is introduced in the previous guidance Train forcaster on single node in detail, therefore we directly create and train a TCNForecaster based on the nyc taxi dataset.

## Speeding up inference#

When a trained forecaster is ready and forecaster is a non-distributed version, we provide with predict_with_onnx method to speed up inference. The method can be directly called without calling build_onnx and forecaster will automatically build an onnxruntime session with default settings.

📝Note

build_onnx is recommended to use in following cases:

1. To strictly control the thread to be used during inferencing.

2. To alleviate the cold start problem when predict_with_onnx is called for the first time.

Please refer to API documentation for more information on build_onnx.

The predict_with_onnx method supports data in following formats:

1. numpy ndarray (recommended)

3. bigdl.chronos.data.TSDataset

And there are batch_size and quantize parameters you may want to change. If not familiar with manual hyperparameters tuning, just leave batch_size to the default value. Additionally, quantize can be set to True to use the quantized onnx model to predict.

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# get data for training and testing
train_data, test_data = get_data()
# get a trained forecaster
forecaster = get_trained_forecaster(train_data)

[ ]:

# speed up inference through ONNXRuntime
for x, y in test_data:
yhat = forecaster.predict_with_onnx(x.numpy()) # predict


Let’s see the acceleration performance of predict_with_onnx.

The predict latency of without accelerator and with ONNXRuntime are given below. The result “p50” means latency sorted to 50% in multiple predictions and the acceleration performance is significant.

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from bigdl.chronos.metric import Evaluator

x = next(iter(test_data))[0]
def func_original():
forecaster.predict(x.numpy()) # without accelerator
def func_onnxruntime():
forecaster.predict_with_onnx(x.numpy()) # with ONNXRuntime

print("original predict runtime (ms):", Evaluator.get_latency(func_original))
print("pridict runtime with ONNXRuntime (ms):", Evaluator.get_latency(func_onnxruntime))