Build PaddlePaddle for Android¶
+There are two approaches to build PaddlePaddle for Android: using Docker and on Linux without Docker.
+Cross-Compiling Using Docker¶
+Docker-based cross-compiling is the recommended approach because Docker runs on all major operating systems, including Linux, Mac OS X, and Windows.
+Build the Docker Image¶
+The following steps pack all the tools that we need to build PaddlePaddle into a Docker image.
+$ git clone https://github.com/PaddlePaddle/Paddle.git
+$ cd Paddle
+$ docker build -t paddle:dev-android . -f Dockerfile.android
+Build the Inference Library¶
+We can run the Docker image we just created to build the inference library of PaddlePaddle for Android using the command below:
+$ docker run -it --rm -v $PWD:/paddle -e "ANDROID_ABI=armeabi-v7a" -e "ANDROID_API=21" paddle:dev-android
+The Docker image accepts two arguments ANDROID_ABI and ANDROID_API:
| Argument | Optional Values | Default |
+|—————–|————————-|———|
+|ANDROID_ABI |armeabi-v7a, arm64-v8a | armeabi-v7a |
+|ANDROID_API |>= 21 | 21 |
The ARM-64 architecture (arm64-v8a) requires at least level 21 of Android API.
The default entry-point of the Docker image, paddle/scripts/docker/build_android.sh generates the Android cross-compiling standalone toolchain based on the argument: ANDROID_ABI or ANDROID_API. For information about other configuration arguments, please continue reading.
The above command generates and outputs the inference library in $PWD/install_android and puts third-party libraries in $PWD/install_android/third_party.
Cross-Compiling on Linux¶
+The Linux-base approach to cross-compile is to run steps in Dockerfile.android manually on a Linux x64 computer.
Setup the Environment¶
+To build for Android’s, we need Android NDK:
+wget -q https://dl.google.com/android/repository/android-ndk-r14b-linux-x86_64.zip
+unzip -q android-ndk-r14b-linux-x86_64.zip
+Android NDK includes everything we need to build the standalone toolchain, which in then used to build PaddlePaddle for Android. (We plan to remove the intermediate stage of building the standalone toolchain in the near future.)
+-
+
To build the standalone toolchain for
+armeabi-v7aand Android API level 21:++your/path/to/android-ndk-r14b-linux-x86_64/build/tools/make-standalone-toolchain.sh \ + --arch=arm --platform=android-21 --install-dir=your/path/to/arm_standalone_toolchain +
The generated standalone toolchain will be in
+your/path/to/arm_standalone_toolchain.
+To build the standalone toolchain for
+arm64-v8aand Android API level 21:++your/path/to/android-ndk-r14b-linux-x86_64/build/tools/make-standalone-toolchain.sh \ + --arch=arm64 --platform=android-21 --install-dir=your/path/to/arm64_standalone_toolchain +
The generated standalone toolchain will be in
+your/path/to/arm64_standalone_toolchain.
+
Please be aware that the minimum level of Android API required by PaddlePaddle is 21.
+Cross-Compiling Arguments¶
+CMake supports choosing the toolchain. PaddlePaddle provides android.cmake, which configures the Android cross-compiling toolchain for CMake. android.cmake is not required for CMake >= 3.7, which support Android cross-compiling. PaddlePaddle detects the CMake version, for those newer than 3.7, it uses the official version.
Some other CMake arguments you need to know:
+-
+
CMAKE_SYSTEM_NAMEmust beAndroid. This tells PaddlePaddle’s CMake system to cross-compile third-party dependencies. This also changes some other CMake arguments likeWITH_GPU=OFF,WITH_AVX=OFF,WITH_PYTHON=OFF, andWITH_RDMA=OFF.
+WITH_C_APImust beON, to build the C-based inference library for Android.
+WITH_SWIG_PYmust beOFFbecause the Android platform doesn’t support SWIG-based API.
+
Some Android-specific arguments:
+-
+
ANDROID_STANDALONE_TOOLCHAIN: the absolute path of the Android standalone toolchain, or the path relative to the CMake build directory. PaddlePaddle’s CMake extensions would derive the cross-compiler, sysroot and Android API level from this argument.
+ANDROID_TOOLCHAIN: could begccorclang. The default value isclang.-
+
- For CMake >= 3.7, it should anyway be
clang. For older versions, it could begcc.
+ - Android’s official
clangrequiresglibc>= 2.15.
+
+- For CMake >= 3.7, it should anyway be
ANDROID_ABI: could bearmeabi-v7aorarm64-v8a. The default value isarmeabi-v7a.
+ANDROID_NATIVE_API_LEVEL: could be derived from the value ofANDROID_STANDALONE_TOOLCHAIN.
+ANROID_ARM_MODE:-
+
- could be
ONorOFF, and defaults toON, whenANDROID_ABI=armeabi-v7a;
+ - no need to specify when
ANDROID_ABI=arm64-v8a.
+
+- could be
ANDROID_ARM_NEON: indicates if to use NEON instructions.-
+
- could be
ONorOFF, and defaults toON, whenANDROID_ABI=armeabi-v7a;
+ - no need to specify when
ANDROID_ABI=arm64-v8a.
+
+- could be
Other useful arguments:
+-
+
USE_EIGEN_FOR_BLAS: indicates if using Eigen. Could beONorOFF, defaults toOFF.
+HOST_C/CXX_COMPILER: specifies the host compiler, which is used to build the host-specific protoc and target-specific OpenBLAS. It defaults to the value of the environment variableCC, orcc.
+
Some frequent configurations for your reference:
+cmake -DCMAKE_SYSTEM_NAME=Android \
+ -DANDROID_STANDALONE_TOOLCHAIN=your/path/to/arm_standalone_toolchain \
+ -DANDROID_ABI=armeabi-v7a \
+ -DANDROID_ARM_NEON=ON \
+ -DANDROID_ARM_MODE=ON \
+ -DUSE_EIGEN_FOR_BLAS=ON \
+ -DCMAKE_INSTALL_PREFIX=your/path/to/install \
+ -DWITH_C_API=ON \
+ -DWITH_SWIG_PY=OFF \
+ ..
+cmake -DCMAKE_SYSTEM_NAME=Android \
+ -DANDROID_STANDALONE_TOOLCHAIN=your/path/to/arm64_standalone_toolchain \
+ -DANDROID_ABI=arm64-v8a \
+ -DUSE_EIGEN_FOR_BLAS=OFF \
+ -DCMAKE_INSTALL_PREFIX=your/path/to/install \
+ -DWITH_C_API=ON \
+ -DWITH_SWIG_PY=OFF \
+ ..
+There are some other arguments you might want to configure.
+-
+
CMAKE_BUILD_TYPE=MinSizeRelminimizes the size of library.
+CMAKE_BUILD_TYPE-Releaseoptimizes the runtime performance.
+
Our own tip for performance optimization to use clang and Eigen or OpenBLAS:
+-
+
CMAKE_BUILD_TYPE=Release
+ANDROID_TOOLCHAIN=clang
+USE_EIGEN_BLAS=ONforarmeabi-v7a, orUSE_EIGEN_FOR_BLAS=OFFforarm64-v8a.
+
Build and Install¶
+After running cmake, we can run make; make install to build and install.
Before building, you might want to remove the third_party and build directories including pre-built libraries for other architectures.
After building，in the directory CMAKE_INSTALL_PREFIX, you will find three sub-directories:
-
+
include: the header file of the inference library,
+lib: the inference library built for various Android ABIs,
+third_party: dependent third-party libraries built for Android.
+