(prototype) Tracing-based Selective Build Mobile Interpreter in Android and iOS =============================================================================== *Author*: Chen Lai , Dhruv Matani .. warning:: Tracing-based selective build a prototype feature to minimize library size. Since the traced result relies on the model input and traced environment, if the tracer runs in a different environment than mobile interpreter, the operator list might be different from the actual used operator list and missing operators error might raise. Introduction ------------ This tutorial introduces a new way to custom build mobile interpreter to further optimize mobile interpreter size. It restricts the set of operators included in the compiled binary to only the set of operators actually needed by target models. It is a technique to reduce the binary size of PyTorch for mobile deployments. Tracing Based Selective Build runs a model with specific representative inputs, and records which operators were called. The build then includes just those operators. Following are the processes to use tracing-based selective approach to build a custom mobile interpreter. 1. *Prepare model with bundled input* .. code:: python import numpy as np import torch import torch.jit import torch.utils import torch.utils.bundled_inputs from PIL import Image from torchvision import transforms # Step 1. Get the model model = torch.hub.load('pytorch/vision:v0.7.0', 'deeplabv3_resnet50', pretrained=True) model.eval() scripted_module = torch.jit.script(model) # Export full jit version model (not compatible lite interpreter), leave it here for comparison scripted_module.save("deeplabv3_scripted.pt") # Export lite interpreter version model (compatible with lite interpreter) # path = "" scripted_module._save_for_lite_interpreter(f"${path}/deeplabv3_scripted.ptl") model_file = f"${path}/deeplabv3_scripted.ptl" # Step 2. Prepare inputs for the model input_image_1 = Image.open(f"${path}/dog.jpg") preprocess = transforms.Compose([ transforms.ToTensor(), transforms.Normalize(mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225]), ]) input_tensor_1 = preprocess(input_image_1) input_batch_1 = input_tensor_1.unsqueeze(0) # create a mini-batch as expected by the model scripted_module = torch.jit.load(model_file) scripted_module.forward(input_batch_1) # optional, to validate the model can run with the input_batch_1 input_image_2 = Image.open(f"${path}/deeplab.jpg") input_tensor_2 = preprocess(input_image_2) input_batch_2 = input_tensor_2.unsqueeze(0) # create a mini-batch as expected by the model scripted_module = torch.jit.load(model_file) scripted_module.forward(input_batch_2) # optional, to validate the model can run with the input_batch_2 # Step 3. Bundle the model with the prepared input from step2. Can bundle as many input as possible. bundled_model_input = [ (torch.utils.bundled_inputs.bundle_large_tensor(input_batch_1), ), (torch.utils.bundled_inputs.bundle_large_tensor(input_batch_2), )] bundled_model = torch.utils.bundled_inputs.bundle_inputs(scripted_module, bundled_model_input) bundled_model._save_for_lite_interpreter(f"${path}/deeplabv3_scripted_with_bundled_input.ptl") 2. Build tracer .. code:: shell MACOSX_DEPLOYMENT_TARGET=10.9 CC=clang CXX=clang++ MAX_JOBS=16 TRACING_BASED=1 python setup.py develop 3. Run tracer with the model with bundled input .. code:: shell ./build/bin/model_tracer --model_input_path ${path}/deeplabv3_scripted_with_bundled_input.ptl --build_yaml_path ${path}/deeplabv3_scripted.yaml Android ------- Get the Image Segmentation demo app in Android: https://github.com/pytorch/android-demo-app/tree/master/ImageSegmentation 1. **Tracing-based build libtorch lite for android**: Build libtorch for android for all 4 android abis (``armeabi-v7a``, ``arm64-v8a``, ``x86``, ``x86_64``) by running .. code-block:: bash SELECTED_OP_LIST=${path}/deeplabv3_scripted.yaml TRACING_BASED=1 ./scripts/build_pytorch_android.sh if it will be tested on Pixel 4 emulator with ``x86``, use cmd ``BUILD_LITE_INTERPRETER=1 ./scripts/build_pytorch_android.sh x86`` to specify abi to save build time. .. code-block:: bash SELECTED_OP_LIST=${path}/deeplabv3_scripted.yaml TRACING_BASED=1 ./scripts/build_pytorch_android.sh x86 After the build finish, it will show the library path: .. code-block:: bash BUILD SUCCESSFUL in 55s 134 actionable tasks: 22 executed, 112 up-to-date + find /Users/chenlai/pytorch/android -type f -name '*aar' + xargs ls -lah -rw-r--r-- 1 chenlai staff 13M Feb 11 11:48 /Users/chenlai/pytorch/android/pytorch_android/build/outputs/aar/pytorch_android-release.aar -rw-r--r-- 1 chenlai staff 36K Feb 9 16:45 /Users/chenlai/pytorch/android/pytorch_android_torchvision/build/outputs/aar/pytorch_android_torchvision-release.aar 2. **Use the PyTorch Android libraries built from source in the ImageSegmentation app**: Create a folder `libs` in the path, the path from repository root will be `ImageSegmentation/app/libs`. Copy `pytorch_android-release` to the path ``ImageSegmentation/app/libs/pytorch_android-release.aar``. Copy `pytorch_android_torchvision` (downloaded from `Pytorch Android Torchvision Nightly `_) to the path ``ImageSegmentation/app/libs/pytorch_android_torchvision.aar``. Update the `dependencies` part of ``ImageSegmentation/app/build.gradle`` to .. code:: gradle dependencies { implementation 'androidx.appcompat:appcompat:1.2.0' implementation 'androidx.constraintlayout:constraintlayout:2.0.2' testImplementation 'junit:junit:4.12' androidTestImplementation 'androidx.test.ext:junit:1.1.2' androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0' implementation(name:'pytorch_android-release', ext:'aar') implementation(name:'pytorch_android_torchvision', ext:'aar') implementation 'com.android.support:appcompat-v7:28.0.0' implementation 'com.facebook.fbjni:fbjni-java-only:0.0.3' } Update `all projects` part in ``ImageSegmentation/build.gradle`` to .. code:: gradle allprojects { repositories { google() jcenter() flatDir { dirs 'libs' } } } 3. **Test app**: Build and run the `ImageSegmentation` app in Android Studio iOS --- Get ImageSegmentation demo app in iOS: https://github.com/pytorch/ios-demo-app/tree/master/ImageSegmentation 1. **Build libtorch lite for iOS**: .. code-block:: bash SELECTED_OP_LIST=${path}/deeplabv3_scripted.yaml TRACING_BASED=1 IOS_PLATFORM=SIMULATOR ./scripts/build_ios.sh 2. **Remove Cocoapods from the project** (this step is only needed if you ran `pod install`): .. code-block:: bash pod deintegrate 3. **Link ImageSegmentation demo app with the custom built library**: Open your project in XCode, go to your project Target’s **Build Phases - Link Binaries With Libraries**, click the **+** sign and add all the library files located in `build_ios/install/lib`. Navigate to the project **Build Settings**, set the value **Header Search Paths** to `build_ios/install/include` and **Library Search Paths** to `build_ios/install/lib`. In the build settings, search for **other linker flags**. Add a custom linker flag below `-all_load`. Finally, disable bitcode for your target by selecting the Build Settings, searching for Enable Bitcode, and set the value to **No**. 4. **Build and test the app in Xcode.** Conclusion ---------- In this tutorial, we demonstrated a new way to custom build PyTorch's efficient mobile interpreter - tracing-based selective build, in an Android and iOS app. We walked through an Image Segmentation example to show how to bundle inputs to a model, generated operator list by tracing the model with bundled input, and build a custom torch library from source with the operator list from tracing result. The custom build is still under development, and we will continue improving its size in the future. Note, however, that the APIs are subject to change in future versions. Thanks for reading! As always, we welcome any feedback, so please create an issue here `. Learn More - To learn more about PyTorch Mobile, please refer to PyTorch Mobile Home Page * To learn more about Image Segmentation, please refer to the Image Segmentation DeepLabV3 on Android Recipe _