Overview
The feedback-directed optimization (FDO) of the kernel allows users to build optimized kernels for different applications to improve the application performance in single-application scenarios. In addition, FDO is integrated GCC for openEuler, and A-FOT provides automatic optimization, enabling users to easily enable FDO.
Installation and Deployment
Software Requirements
- OS: openEuler 22.03 LTS SP3
Hardware Requirements
- Architecture: AArch64 or x86_64
Software Installation
Downloading the Kernel Source Code
yum install -y kernel-source
cp -r /usr/src/linux-5.10.0-153.12.0.89.oe2203sp3.aarch64 .
Note: Change the version number as required.
(Optional) Installing GCC
GCC of openEuler 22.03 LTS SP3 can compile kernels with PGO. Alternatively, you can perform the following steps to manually build a customized GCC based on other GCC versions (GCC 10 or later). The key is to add --disable-tls --disable-libsanitizer during configuration.
cd ${GCC_DIR}
mkdir build
cd build
../configure --prefix=${GCC_INSTALL_PREFIX} --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-linker-hash-style=gnu --enable-languages=c,c++,objc,obj-c++,fortran,lto --enable-plugin --enable-initfini-array --disable-libgcj --without-isl --without-cloog --enable-gnu-indirect-function --build=aarch64-linux-gnu --with-stage1-ldflags='-Wl,-z,relro,-z,now' --with-boot-ldflags='-Wl,-z,relro,-z,now' --disable-bootstrap --with-multilib-list=lp64 --enable-bolt --disable-tls --disable-libsanitizer
make -j 96 && make install -j 96
Installing A-FOT
git clone https://gitee.com/openeuler/A-FOT.git
Usage
You can use A-FOT to enable kernel FDO and obtain the optimized kernel by specifying opt_mode as Auto_kernel_PGO. Other configuration items can be specified on the CLI, for example, ./a-fot --pgo_phase 1. -s and -n options can be specified on CLI only. Options related to kernel FDO are as follows.
| No. | Option (Configuration File) | Description | Default Value |
|---|---|---|---|
| 1 | config_file | Path of the configuration file. User configurations are read from this file. | ${afot_path}/a-fot.ini |
| 2 | opt_mode | Optimization mode to be executed by the tool. The value can be AutoFDO, AutoPrefetch, AutoBOLT, or Auto_kernel_PGO. | AutoPrefetch |
| 3 | pgo_mode | Kernel FDO mode, which can be GCOV or full PGO. | all |
| 4 | pgo_phase | FDO execution phase. | 1 |
| 5 | kernel_src | Kernel source code directory. If this option is not specified, the tool automatically downloads the source code. | None (optional) |
| 6 | kernel_name | File name of the kernel build. The tool will add the -pgoing or -pgoed suffix depending on the phase. | kernel |
| 7 | work_path | Script working directory, which is used to store log files, wrappers, and profiles. | /opt (/tmp cannot be used.) |
| 8 | run_script | Application execution script. The user needs to write the script, which will be used by the tool to execute the target application. | /root/run.sh |
| 9 | gcc_path | GCC path. | /usr |
After configuring the compilation options, run the following command to use A-FOT to automatically optimize the kernel:
a-fot --config_file ./a-fot.ini -s
Note: The -s option instructs A-FOT to automatically reboot into the compiled kernel. If you do not want the tool to automatically perform this sensitive operation, omit this option. However, you need to manually reboot and perform the second phase (--pgo_phase 2).
Compatibility
This section describes the compatibility issues in some special scenarios. This project is in continuous iteration and issues will be fixed as soon as possible. Developers are welcome to join this project.
- The implementation of FDO in the GCC varies with the version. Therefore, GCC 10 or later is required.
