Sparsity preserving clustering Keras example

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Overview

This is an end to end example showing the usage of the sparsity preserving clustering 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 sparsity and see the accuracy and observe that the model was successfully pruned.
  3. Apply weight clustering to the pruned model and observe the loss of sparsity.
  4. Apply sparsity preserving clustering on the pruned model and observe that the sparsity applied earlier has been preserved.
  5. Generate a TFLite model and check that the accuracy has been preserved in the pruned clustered model.
  6. Compare the sizes of the different models to observe the compression benefits of applying sparsity followed by the collaborative optimization technique of sparsity preserving clustering.

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)
])

# Train the digit classification model
model.compile(optimizer='adam',
              loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True),
              metrics=['accuracy'])

model.fit(
    train_images,
    train_labels,
    validation_split=0.1,
    epochs=10
)
Epoch 1/10
1688/1688 [==============================] - 8s 4ms/step - loss: 0.3112 - accuracy: 0.9121 - val_loss: 0.1266 - val_accuracy: 0.9673
Epoch 2/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.1215 - accuracy: 0.9662 - val_loss: 0.0795 - val_accuracy: 0.9783
Epoch 3/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0845 - accuracy: 0.9756 - val_loss: 0.0654 - val_accuracy: 0.9820
Epoch 4/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0685 - accuracy: 0.9802 - val_loss: 0.0601 - val_accuracy: 0.9825
Epoch 5/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0586 - accuracy: 0.9823 - val_loss: 0.0592 - val_accuracy: 0.9833
Epoch 6/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0522 - accuracy: 0.9845 - val_loss: 0.0532 - val_accuracy: 0.9858
Epoch 7/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0468 - accuracy: 0.9860 - val_loss: 0.0571 - val_accuracy: 0.9847
Epoch 8/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0423 - accuracy: 0.9873 - val_loss: 0.0543 - val_accuracy: 0.9842
Epoch 9/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0383 - accuracy: 0.9883 - val_loss: 0.0535 - val_accuracy: 0.9860
Epoch 10/10
1688/1688 [==============================] - 7s 4ms/step - loss: 0.0346 - accuracy: 0.9895 - val_loss: 0.0574 - val_accuracy: 0.9848
<tensorflow.python.keras.callbacks.History at 0x7f8e9c4170d0>

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)
Baseline test accuracy: 0.9812999963760376
Saving model to:  /tmp/tmpfua4ka97.h5

Prune and fine-tune the model to 50% sparsity

Apply the prune_low_magnitude() API to prune the whole pre-trained model to achieve the model that is to be clustered in the next step. For how best to use the API to achieve the best compression rate while maintaining your target accuracy, refer to the pruning comprehensive guide.

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'])

pruned_model.summary()
/tmpfs/src/tf_docs_env/lib/python3.7/site-packages/tensorflow/python/keras/engine/base_layer.py:2191: UserWarning: `layer.add_variable` is deprecated and will be removed in a future version. Please use `layer.add_weight` method instead.
  warnings.warn('`layer.add_variable` is deprecated and '
Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
prune_low_magnitude_reshape  (None, 28, 28, 1)         1         
_________________________________________________________________
prune_low_magnitude_conv2d ( (None, 26, 26, 12)        230       
_________________________________________________________________
prune_low_magnitude_max_pool (None, 13, 13, 12)        1         
_________________________________________________________________
prune_low_magnitude_flatten  (None, 2028)              1         
_________________________________________________________________
prune_low_magnitude_dense (P (None, 10)                40572     
=================================================================
Total params: 40,805
Trainable params: 20,410
Non-trainable params: 20,395
_________________________________________________________________

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)
Epoch 1/3
WARNING:tensorflow:From /tmpfs/src/tf_docs_env/lib/python3.7/site-packages/tensorflow/python/ops/array_ops.py:5049: calling gather (from tensorflow.python.ops.array_ops) with validate_indices is deprecated and will be removed in a future version.
Instructions for updating:
The `validate_indices` argument has no effect. Indices are always validated on CPU and never validated on GPU.
1688/1688 [==============================] - 9s 5ms/step - loss: 0.0931 - accuracy: 0.9696 - val_loss: 0.0878 - val_accuracy: 0.9755
Epoch 2/3
1688/1688 [==============================] - 8s 4ms/step - loss: 0.0597 - accuracy: 0.9813 - val_loss: 0.0732 - val_accuracy: 0.9802
Epoch 3/3
1688/1688 [==============================] - 8s 4ms/step - loss: 0.0499 - accuracy: 0.9849 - val_loss: 0.0689 - val_accuracy: 0.9822
<tensorflow.python.keras.callbacks.History at 0x7f8e9c3566d0>

Define helper functions to calculate and print the sparsity 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})",
            )

Check that the model kernels was correctly pruned. We need to strip the pruning wrapper first. We also create a deep copy of the model to be used in the next step.

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

print_model_weights_sparsity(stripped_pruned_model)

stripped_pruned_model_copy = tf.keras.models.clone_model(stripped_pruned_model)
stripped_pruned_model_copy.set_weights(stripped_pruned_model.get_weights())
conv2d/kernel:0: 50.00% sparsity  (54/108)
dense/kernel:0: 50.00% sparsity  (10140/20280)

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

Next, we apply both clustering and sparsity preserving clustering on the pruned model and observe that the latter preserves sparsity on your pruned model. Note that we stripped pruning wrappers from the pruned model with tfmot.sparsity.keras.strip_pruning before applying the clustering API.

# Clustering
cluster_weights = tfmot.clustering.keras.cluster_weights
CentroidInitialization = tfmot.clustering.keras.CentroidInitialization

clustering_params = {
  'number_of_clusters': 8,
  'cluster_centroids_init': CentroidInitialization.KMEANS_PLUS_PLUS
}

clustered_model = cluster_weights(stripped_pruned_model, **clustering_params)

clustered_model.compile(optimizer='adam',
              loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True),
              metrics=['accuracy'])

print('Train clustering model:')
clustered_model.fit(train_images, train_labels,epochs=3, validation_split=0.1)


stripped_pruned_model.save("stripped_pruned_model_clustered.h5")

# Sparsity preserving clustering
from tensorflow_model_optimization.python.core.clustering.keras.experimental import (
    cluster,
)

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_copy, **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)
Train clustering model:
Epoch 1/3
1688/1688 [==============================] - 8s 5ms/step - loss: 0.0404 - accuracy: 0.9873 - val_loss: 0.0608 - val_accuracy: 0.9845
Epoch 2/3
1688/1688 [==============================] - 8s 5ms/step - loss: 0.0386 - accuracy: 0.9879 - val_loss: 0.0599 - val_accuracy: 0.9842
Epoch 3/3
1688/1688 [==============================] - 8s 5ms/step - loss: 0.0394 - accuracy: 0.9873 - val_loss: 0.0599 - val_accuracy: 0.9842
WARNING:tensorflow:Compiled the loaded model, but the compiled metrics have yet to be built. `model.compile_metrics` will be empty until you train or evaluate the model.
Train sparsity preserving clustering model:
Epoch 1/3
1688/1688 [==============================] - 8s 5ms/step - loss: 0.0411 - accuracy: 0.9873 - val_loss: 0.0570 - val_accuracy: 0.9840
Epoch 2/3
1688/1688 [==============================] - 8s 5ms/step - loss: 0.0409 - accuracy: 0.9865 - val_loss: 0.0559 - val_accuracy: 0.9835
Epoch 3/3
1688/1688 [==============================] - 8s 5ms/step - loss: 0.0397 - accuracy: 0.9872 - val_loss: 0.0582 - val_accuracy: 0.9853
<tensorflow.python.keras.callbacks.History at 0x7f8e2c447bd0>

Check sparsity for both models.

print("Clustered Model sparsity:\n")
print_model_weights_sparsity(clustered_model)
print("\nSparsity preserved clustered Model sparsity:\n")
print_model_weights_sparsity(sparsity_clustered_model)
Clustered Model sparsity:

conv2d/kernel:0: 0.00% sparsity  (0/108)
dense/kernel:0: 0.98% sparsity  (198/20280)

Sparsity preserved clustered Model sparsity:

conv2d/kernel:0: 50.00% sparsity  (54/108)
dense/kernel:0: 50.00% sparsity  (10140/20280)

Create 1.6x smaller models from clustering

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
# Clustered model
clustered_model_file = 'clustered_model.h5'

# Save the model.
clustered_model.save(clustered_model_file)

#Sparsity Preserve Clustered model
sparsity_clustered_model_file = 'sparsity_clustered_model.h5'

# Save the model.
sparsity_clustered_model.save(sparsity_clustered_model_file)

print("Clustered Model size: ", get_gzipped_model_size(clustered_model_file), ' KB')
print("Sparsity preserved clustered Model size: ", get_gzipped_model_size(sparsity_clustered_model_file), ' KB')
Clustered Model size:  245.456  KB
Sparsity preserved clustered Model size:  154.102  KB

Create a TFLite model from combining sparsity preserving weight clustering and post-training quantization

Strip clustering wrappers and convert to TFLite.

stripped_sparsity_clustered_model = tfmot.clustering.keras.strip_clustering(sparsity_clustered_model)

converter = tf.lite.TFLiteConverter.from_keras_model(stripped_sparsity_clustered_model)
converter.optimizations = [tf.lite.Optimize.DEFAULT]
sparsity_clustered_quant_model = converter.convert()

_, pruned_and_clustered_tflite_file = tempfile.mkstemp('.tflite')

with open(pruned_and_clustered_tflite_file, 'wb') as f:
  f.write(sparsity_clustered_quant_model)

print("Sparsity preserved clustered Model size: ", get_gzipped_model_size(sparsity_clustered_model_file), ' KB')
print("Sparsity preserved clustered and quantized TFLite model size:",
       get_gzipped_model_size(pruned_and_clustered_tflite_file), ' KB')
WARNING:tensorflow:Compiled the loaded model, but the compiled metrics have yet to be built. `model.compile_metrics` will be empty until you train or evaluate the model.
INFO:tensorflow:Assets written to: /tmp/tmp8wy5vqee/assets
Sparsity preserved clustered Model size:  154.102  KB
Sparsity preserved clustered and quantized TFLite model size: 7.6  KB

See the persistence of accuracy from TF to TFLite

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

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

# Keras model evaluation
stripped_sparsity_clustered_model.compile(optimizer='adam',
              loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True),
              metrics=['accuracy'])
_, sparsity_clustered_keras_accuracy = stripped_sparsity_clustered_model.evaluate(
    test_images, test_labels, verbose=0)

# TFLite model evaluation
interpreter = tf.lite.Interpreter(pruned_and_clustered_tflite_file)
interpreter.allocate_tensors()

sparsity_clustered_tflite_accuracy = eval_model(interpreter)

print('Pruned, clustered and quantized Keras model accuracy:', sparsity_clustered_keras_accuracy)
print('Pruned, clustered and quantized TFLite model accuracy:', sparsity_clustered_tflite_accuracy)
Evaluated on 0 results so far.
Evaluated on 1000 results so far.
Evaluated on 2000 results so far.
Evaluated on 3000 results so far.
Evaluated on 4000 results so far.
Evaluated on 5000 results so far.
Evaluated on 6000 results so far.
Evaluated on 7000 results so far.
Evaluated on 8000 results so far.
Evaluated on 9000 results so far.


Pruned, clustered and quantized Keras model accuracy: 0.978600025177002
Pruned, clustered and quantized TFLite model accuracy: 0.9785

Conclusion

In this tutorial, you learned how to create a model, prune it using the prune_low_magnitude() API, and apply sparsity preserving clustering to preserve sparsity while clustering the weights. The sparsity preserving clustered model was compared to a clustered one to show that sparsity is preserved in the former and lost in the latter. Next, the pruned clustered model was converted to TFLite to show the compression benefits of chaining the pruning and sparsity preserving clustering model optimization techniques and, finally, the TFLite model was evaluated to ensure that the accuracy persists in the TFLite backend.