Use GCC's PGO (profile guided optimization) to optimize the entire system

inspire

It comes from the experiment made by megahard on its own server , No more nonsense, just go to the picture above

Microsoft's approach

Microsoft's approach

You can see the use of PGO The optimized kernel still has some performance improvements

zero 、 Premise

Want to use PGO Compile optimization , Yours gcc The compiler needs to turn on support pgo characteristic ,gentoo The system is as follows

sudo vim /etc/portage/make.conf:
USE="pgo"

sudo emerge gcc

One 、 kernel kernel The optimization of the

cd /usr/src/linux
sudo make clean
sudo make menuconfig：
CONFIG_DEBUG_FS=y
CONFIG_GCOV_KERNEL=y
CONFIG_GCOV_PROFILE_ALL=y

sudo make KCFLAGS=“-fprofile-dir=/kernel-pgo/”

 Final installation kernel And update the grub
sudo make install
sudo grub-config -o /boot/grub/grub.cfg

 Restart the system 
sudo reboot

Then run the system under the new kernel for a while , Open various software such as browser 、mpv player 、cmus、 office 、 Compiling software 、 download 、 game 、steam wait （ I will run through all the software and scenarios of the daily system ）, So that the kernel can collect enough profile data （gcov data ）

# notes ： Open the CONFIG_DEBUG_FS=y、CONFIG_GCOV_KERNEL=y Characteristic kernel Performance will be significantly reduced , But this pair of collections is used for PGO Optimization of the profile Data is necessary

kernel PGO Optimization of the profile The data is stored in /sys/kernel/debug/gcov/kernel-pgo/ Under the table of contents , There are many small files , The format is similar to "#usr#src#linux#arch#x86#crypto#aesni-intel_glue.gcda"

sudo cp -r /sys/kernel/debug/gcov/kernel-pgo/ /
cd /usr/src/linux
sudo make clean
sudo make menuconfig:
CONFIG_DEBUG_FS=n
CONFIG_GCOV_KERNEL=n
CONFIG_GCOV_PROFILE_ALL=n

sudo make KCFLAGS=“-fprofile-use -fprofile-dir=/kernel-pgo/ -fprofile-correction -Wno-coverage-mismatch -Wno-error=coverage-mismatch”

 Final installation kernel And update the grub
sudo make install
sudo grub-config -o /boot/grub/grub.cfg

 Restart the system 
sudo reboot

Okay , Now you can experience PGO What is the performance of the optimized kernel , Open the game to test fps Well , Is it higher than the original kernel frame number ？

Add ： Use Clang Of LTO Optimize compilation kernel

since kernel 5.12 The start kernel allows lto To optimize the , However, it is limited to support clang+llvm compiler , I won't support it gcc, So you have to install it first clang and llvm, as well as lld The linker . The steps are simple ——

sudo make LLVM=1 LLVM_IAS=1 menuconfig:
CONFIG_DEBUG_FS=n
CONFIG_GCOV_KERNEL=n
CONFIG_GCOV_PROFILE_ALL=n
CONFIG_LTO_CLANG_FULL=y


 then 
sudo make LLVM=1 LLVM_IAS=1

that will do .

# notes ： at present clang Kernel is not supported gcov Optimize , So the above gcc Of pgo and clang Of lto You can only choose one of the two optimization schemes .

If you don't think the regular kernel can satisfy you , You can also try compiling it yourself xanmod The kernel project , Compared with the conventional kernel, it has done a lot of update optimization （ For example, open O3 Level compilation optimization ）——

https://www.xanmod.org/​www.xanmod.org/

# Click... On the web page “tarball” You can download it. xanmod Kernel source package .

Two 、 Of all program software in the whole system PGO Optimize

First you need to turn off portage Two security features of the build system

sudo vim /etc/portage/make.conf:
FEATURES="-sandbox -usersandbox"

Then add the following gcc Compile parameters

sudo vim /etc/portage/make.conf:
COMMON_FLAGS="$( Your own original compilation optimization parameters ) -fprofile-generate -fprofile-dir=/portage-pgo/"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"
LDFLAGS="${COMMON_FLAGS} -Wl,-O3 -Wl,--as-needed -Wl,--hash-style=gnu -Wl,--sort-common -Wl,--strip-all -ljemalloc -Wl,-ljemalloc"

EMERGE_DEFAULT_OPTS="--with-bdeps=y --ask --deep --verbose=y --load-average --keep-going"


sudo mkdir /portage-pgo/

Now start compiling the entire system

sudo emerge -e @world

Restart the system after compilation

sudo reboot

Then run the system under the new system for a period of time , Open various software such as browser 、mpv player 、cmus、 office 、 Compiling software 、 download 、 game 、steam wait （ I will run through all the software and scenarios of the daily system , Recommended 1-2 God ）, To collect enough comprehensive profile data （gcov data ）, Each program PGO Optimization of the profile The data is stored in /portage-pgo/ Under the table of contents

# notes ： Open the -fprofile-generate The program performance of the feature will decrease significantly , But this pair of collections is used for PGO Optimization of the profile Data is necessary

Restart the system

sudo reboot

And then modify gcc Compile parameters

sudo vim /etc/portage/make.conf:
COMMON_FLAGS="$( Your own original compilation optimization parameters ) -fprofile-use -fprofile-dir=/portage-pgo/ -fprofile-correction -Wno-error=missing-profile"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"
LDFLAGS="${COMMON_FLAGS} -Wl,-O3 -Wl,--as-needed -Wl,--hash-style=gnu -Wl,--sort-common -Wl,--strip-all -ljemalloc -Wl,-ljemalloc"

Compile the entire system again to use PGO Optimize （ Turn on pgo After optimization, the compilation speed will be greatly improved , It won't be as long as the last time ）

sudo emerge -e @world

Restart the system after compilation

sudo reboot

Okay , Now you can experience PGO Comprehensive compilation optimization gentoo The system , Is it the ultimate performance ？

Use GCC Of PGO（Profile-guided Optimization） Optimize the whole system - You know