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tensorflow
GitHub Repository: tensorflow/docs-l10n
Path: blob/master/site/en-snapshot/model_optimization/guide/combine/pcqat_example.ipynb
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Kernel: Python 3

Copyright 2021 The TensorFlow Authors.

#@title Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # https://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License.

Sparsity and cluster preserving quantization aware training (PCQAT) Keras example

Overview

This is an end to end example showing the usage of the sparsity and cluster preserving quantization aware training (PCQAT) API, part of the TensorFlow Model Optimization Toolkit's collaborative optimization pipeline.

Other pages

For an introduction to the pipeline and other available techniques, see the collaborative optimization overview page.

Contents

In the tutorial, you will:

  1. Train a tf.keras model for the MNIST dataset from scratch.

  2. Fine-tune the model with pruning and see the accuracy and observe that the model was successfully pruned.

  3. Apply sparsity preserving clustering on the pruned model and observe that the sparsity applied earlier has been preserved.

  4. Apply QAT and observe the loss of sparsity and clusters.

  5. Apply PCQAT and observe that both sparsity and clustering applied earlier have been preserved.

  6. Generate a TFLite model and observe the effects of applying PCQAT on it.

  7. Compare the sizes of the different models to observe the compression benefits of applying sparsity followed by the collaborative optimization techniques of sparsity preserving clustering and PCQAT.

  8. Compare the accurracy of the fully optimized model with the un-optimized baseline model accuracy.

Setup

You can run this Jupyter Notebook in your local virtualenv or colab. For details of setting up dependencies, please refer to the installation guide.

! pip install -q tensorflow-model-optimization
import tensorflow as tf import numpy as np import tempfile import zipfile import os

Train a tf.keras model for MNIST to be pruned and clustered

# Load MNIST dataset mnist = tf.keras.datasets.mnist (train_images, train_labels), (test_images, test_labels) = mnist.load_data() # Normalize the input image so that each pixel value is between 0 to 1. train_images = train_images / 255.0 test_images = test_images / 255.0 model = tf.keras.Sequential([ tf.keras.layers.InputLayer(input_shape=(28, 28)), tf.keras.layers.Reshape(target_shape=(28, 28, 1)), tf.keras.layers.Conv2D(filters=12, kernel_size=(3, 3), activation=tf.nn.relu), tf.keras.layers.MaxPooling2D(pool_size=(2, 2)), tf.keras.layers.Flatten(), tf.keras.layers.Dense(10) ]) opt = tf.keras.optimizers.Adam(learning_rate=1e-3) # Train the digit classification model model.compile(optimizer=opt, loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True), metrics=['accuracy']) model.fit( train_images, train_labels, validation_split=0.1, epochs=10 )

Evaluate the baseline model and save it for later usage

_, baseline_model_accuracy = model.evaluate( test_images, test_labels, verbose=0) print('Baseline test accuracy:', baseline_model_accuracy) _, keras_file = tempfile.mkstemp('.h5') print('Saving model to: ', keras_file) tf.keras.models.save_model(model, keras_file, include_optimizer=False)

Prune and fine-tune the model to 50% sparsity

Apply the prune_low_magnitude() API to achieve the pruned model that is to be clustered in the next step. Refer to the pruning comprehensive guide for more information on the pruning API.

Define the model and apply the sparsity API

Note that the pre-trained model is used.

import tensorflow_model_optimization as tfmot prune_low_magnitude = tfmot.sparsity.keras.prune_low_magnitude pruning_params = { 'pruning_schedule': tfmot.sparsity.keras.ConstantSparsity(0.5, begin_step=0, frequency=100) } callbacks = [ tfmot.sparsity.keras.UpdatePruningStep() ] pruned_model = prune_low_magnitude(model, **pruning_params) # Use smaller learning rate for fine-tuning opt = tf.keras.optimizers.Adam(learning_rate=1e-5) pruned_model.compile( loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True), optimizer=opt, metrics=['accuracy'])

Fine-tune the model, check sparsity, and evaluate the accuracy against baseline

Fine-tune the model with pruning for 3 epochs.

# Fine-tune model pruned_model.fit( train_images, train_labels, epochs=3, validation_split=0.1, callbacks=callbacks)

Define helper functions to calculate and print the sparsity and clusters of the model.

def print_model_weights_sparsity(model): for layer in model.layers: if isinstance(layer, tf.keras.layers.Wrapper): weights = layer.trainable_weights else: weights = layer.weights for weight in weights: if "kernel" not in weight.name or "centroid" in weight.name: continue weight_size = weight.numpy().size zero_num = np.count_nonzero(weight == 0) print( f"{weight.name}: {zero_num/weight_size:.2%} sparsity ", f"({zero_num}/{weight_size})", ) def print_model_weight_clusters(model): for layer in model.layers: if isinstance(layer, tf.keras.layers.Wrapper): weights = layer.trainable_weights else: weights = layer.weights for weight in weights: # ignore auxiliary quantization weights if "quantize_layer" in weight.name: continue if "kernel" in weight.name: unique_count = len(np.unique(weight)) print( f"{layer.name}/{weight.name}: {unique_count} clusters " )

Let's strip the pruning wrapper first, then check that the model kernels were correctly pruned.

stripped_pruned_model = tfmot.sparsity.keras.strip_pruning(pruned_model) print_model_weights_sparsity(stripped_pruned_model)

Apply sparsity preserving clustering and check its effect on model sparsity in both cases

Next, apply sparsity preserving clustering on the pruned model and observe the number of clusters and check that the sparsity is preserved.

import tensorflow_model_optimization as tfmot from tensorflow_model_optimization.python.core.clustering.keras.experimental import ( cluster, ) cluster_weights = tfmot.clustering.keras.cluster_weights CentroidInitialization = tfmot.clustering.keras.CentroidInitialization cluster_weights = cluster.cluster_weights clustering_params = { 'number_of_clusters': 8, 'cluster_centroids_init': CentroidInitialization.KMEANS_PLUS_PLUS, 'preserve_sparsity': True } sparsity_clustered_model = cluster_weights(stripped_pruned_model, **clustering_params) sparsity_clustered_model.compile(optimizer='adam', loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True), metrics=['accuracy']) print('Train sparsity preserving clustering model:') sparsity_clustered_model.fit(train_images, train_labels,epochs=3, validation_split=0.1)

Strip the clustering wrapper first, then check that the model is correctly pruned and clustered.

stripped_clustered_model = tfmot.clustering.keras.strip_clustering(sparsity_clustered_model) print("Model sparsity:\n") print_model_weights_sparsity(stripped_clustered_model) print("\nModel clusters:\n") print_model_weight_clusters(stripped_clustered_model)

Apply QAT and PCQAT and check effect on model clusters and sparsity

Next, apply both QAT and PCQAT on the sparse clustered model and observe that PCQAT preserves weight sparsity and clusters in your model. Note that the stripped model is passed to the QAT and PCQAT API.

# QAT qat_model = tfmot.quantization.keras.quantize_model(stripped_clustered_model) qat_model.compile(optimizer='adam', loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True), metrics=['accuracy']) print('Train qat model:') qat_model.fit(train_images, train_labels, batch_size=128, epochs=1, validation_split=0.1) # PCQAT quant_aware_annotate_model = tfmot.quantization.keras.quantize_annotate_model( stripped_clustered_model) pcqat_model = tfmot.quantization.keras.quantize_apply( quant_aware_annotate_model, tfmot.experimental.combine.Default8BitClusterPreserveQuantizeScheme(preserve_sparsity=True)) pcqat_model.compile(optimizer='adam', loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True), metrics=['accuracy']) print('Train pcqat model:') pcqat_model.fit(train_images, train_labels, batch_size=128, epochs=1, validation_split=0.1)
print("QAT Model clusters:") print_model_weight_clusters(qat_model) print("\nQAT Model sparsity:") print_model_weights_sparsity(qat_model) print("\nPCQAT Model clusters:") print_model_weight_clusters(pcqat_model) print("\nPCQAT Model sparsity:") print_model_weights_sparsity(pcqat_model)

See compression benefits of PCQAT model

Define helper function to get zipped model file.

def get_gzipped_model_size(file): # It returns the size of the gzipped model in kilobytes. _, zipped_file = tempfile.mkstemp('.zip') with zipfile.ZipFile(zipped_file, 'w', compression=zipfile.ZIP_DEFLATED) as f: f.write(file) return os.path.getsize(zipped_file)/1000

Observe that applying sparsity, clustering and PCQAT to a model yields significant compression benefits.

# QAT model converter = tf.lite.TFLiteConverter.from_keras_model(qat_model) converter.optimizations = [tf.lite.Optimize.DEFAULT] qat_tflite_model = converter.convert() qat_model_file = 'qat_model.tflite' # Save the model. with open(qat_model_file, 'wb') as f: f.write(qat_tflite_model) # PCQAT model converter = tf.lite.TFLiteConverter.from_keras_model(pcqat_model) converter.optimizations = [tf.lite.Optimize.DEFAULT] pcqat_tflite_model = converter.convert() pcqat_model_file = 'pcqat_model.tflite' # Save the model. with open(pcqat_model_file, 'wb') as f: f.write(pcqat_tflite_model) print("QAT model size: ", get_gzipped_model_size(qat_model_file), ' KB') print("PCQAT model size: ", get_gzipped_model_size(pcqat_model_file), ' KB')

See the persistence of accuracy from TF to TFLite

Define a helper function to evaluate the TFLite model on the test dataset.

def eval_model(interpreter): input_index = interpreter.get_input_details()[0]["index"] output_index = interpreter.get_output_details()[0]["index"] # Run predictions on every image in the "test" dataset. prediction_digits = [] for i, test_image in enumerate(test_images): if i % 1000 == 0: print(f"Evaluated on {i} results so far.") # Pre-processing: add batch dimension and convert to float32 to match with # the model's input data format. test_image = np.expand_dims(test_image, axis=0).astype(np.float32) interpreter.set_tensor(input_index, test_image) # Run inference. interpreter.invoke() # Post-processing: remove batch dimension and find the digit with highest # probability. output = interpreter.tensor(output_index) digit = np.argmax(output()[0]) prediction_digits.append(digit) print('\n') # Compare prediction results with ground truth labels to calculate accuracy. prediction_digits = np.array(prediction_digits) accuracy = (prediction_digits == test_labels).mean() return accuracy

Evaluate the model, which has been pruned, clustered and quantized, and then see that the accuracy from TensorFlow persists in the TFLite backend.

interpreter = tf.lite.Interpreter(pcqat_model_file) interpreter.allocate_tensors() pcqat_test_accuracy = eval_model(interpreter) print('Pruned, clustered and quantized TFLite test_accuracy:', pcqat_test_accuracy) print('Baseline TF test accuracy:', baseline_model_accuracy)

Conclusion

In this tutorial, you learned how to create a model, prune it using the prune_low_magnitude() API, and apply sparsity preserving clustering using the cluster_weights() API to preserve sparsity while clustering the weights.

Next, sparsity and cluster preserving quantization aware training (PCQAT) was applied to preserve model sparsity and clusters while using QAT. The final PCQAT model was compared to the QAT one to show that sparsity and clusters are preserved in the former and lost in the latter.

Next, the models were converted to TFLite to show the compression benefits of chaining sparsity, clustering, and PCQAT model optimization techniques and the TFLite model was evaluated to ensure that the accuracy persists in the TFLite backend.

Finally, the PCQAT TFLite model accuracy was compared to the pre-optimization baseline model accuracy to show that collaborative optimization techniques managed to achieve the compression benefits while maintaining a similar accuracy compared to the original model.