23.12.01 최초 작성
23.12.08 실습 추가

1. CPU Idle

• 동적으로 cpu를 enable/disable할 수 있는 기능 (Armv7~)

---

ls /sys/devices/system/cpu/						//사용가능 cpu 확인
$ cpu0 cpu1 cpu2 cpu3 ... online offline

cat /sys/devices/system/cpu/cpu3/online			//online여부 확인
$ 1

echo 0 > /sys/devices/system/cpu/cpu3/online	//cpu off
echo 0 | sudo tee /sys/devices/system/cpu/cpu3/online
$ 0

grep processor /proc/cpuinfo					//확인

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2. CPU frequency

• CPUfreq : cpu의 clock을 조절할 수 있는 리눅스 서브시스템
• Governor : cpu의 clock 설정
• 코어마다 다른 Governor적용 가능

2.1 Governor 설정

• Performance : 가장 높은 freq으로 설정

• Powersave : 가장 낮은 freq으로 설정

• Userspace : 사용자가 freq 설정

• Ondemand : 현재 시스템의 부하에 따라 조절

• Conservative : Ondemand와 같으나 점진적으로 조절

• Schedutil : 커널 스케줄러에 따라 조절

---

echo conservative |sudo tee /sys/devices/system/cpu/cpufreq/policy0/scaling_governor

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2.2 Governor 개별 설정

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cd /sys/devices/system/cpu/cpu01/cpufre
ls

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• affected_cpus : freq 조절에 영향을 받는 online cpu

• cpuinfo_cur_freq : 현재 실제로 CPU가 동작하는 하드웨어 frequency (kHz)

• cpuinfo_min_freq : 최소 frequency, cpuinfo_max_freq: 최대 frequency

• cpuinfo_transition_latency : 두 frequency 사이의 변경 지연시간 (ns)

• related_cpus : freq 조절에 영향을 받는 online + offline cpu

• scaling_available_frequencies : 변경 가능 frequencies

• scaling_available_governors : 사용 가능 governor

• scaling_cur_freq : Governor가 결정한 현재 frequency

• scaling_min_freq, scaling_max_freq : Governor에서 허용되는 최소/최대 frequency

• scaling_setspeed : userspace governor 에서 설정한 frequency

3. 실습

3.1 타겟 buildroot 다운로드

git clone https://github.com/raspberrypi/buildroot

• 빌드 설정을 rpi4로

cd buildroot
make raspberrypi4_64_defconfig

• Kconfig 설정

//	Kconfig, menuconfig 설정
make linux-menuconfig

//minimal rootfs 설정 (qemu를 위한 buildroot 설정)
make menuconfig

3.2 cpufreq_mygovernor.c 작성 및 makefile 수정

• cpufreq_mygovernor.c

---

#include <linux/cpufreq.h>
#include <linux/init.h>
#include <linux/module.h>

static void cpufreq_mygovernor_limits(struct cpufreq_policy *policy)
{
	        pr_debug("setting to %u kHz\n", policy->max-100000);
	        __cpufreq_driver_target(policy, policy->max-100000, CPUFREQ_RELATION_H);
}

static struct cpufreq_governor cpufreq_mygovernor = {
	.name           = "mygovernor",
	.owner          = THIS_MODULE,
	.flags          = CPUFREQ_GOV_STRICT_TARGET,
	.limits         = cpufreq_mygovernor_limits,

};


#ifdef CONFIG_CPU_FREQ_MYGOVERNOR

struct cpufreq_governor *cpufreq_default_governor(void)

{

	        return &cpufreq_mygovernor;

}

#endif

MODULE_AUTHOR("someone");

MODULE_DESCRIPTION("CPUfreq policy governor 'mygovernor'");

MODULE_LICENSE("GPL");

cpufreq_governor_init(cpufreq_mygovernor);

cpufreq_governor_exit(cpufreq_mygovernor);

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//	/buildroot/output/build/linux-headers-custom/drivers/cpufreq에 
//	cpufreq_mygovernor.c 저장 및 Makefile, Kconfig 수정

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• Makefile 수정
  
• Kconfig 수정
  

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3.3 다시 menuconfig 및 make

• 다시 /buildroot로 돌아와 make clean 실행
• make linux-menuconfig에서
  -> CPU Power Management -> CPU Frequency scaling -> cpufreq_mygovernor (확인 안됨)
• make menuconfig
• make

---

• make linux-menuconfig
  
  
  

sudo apt install libcpufreq-dev
sudo apt-get install libstdc++6 

arm-linux-gnueabihf-gcc -o cpufreq_mygovernor.o cpufreq_mygovernor.c
aarch64-linux-gnu-gcc -o cpufreq_mygovernor.o cpufreq_mygovernor.c

aarch64-linux-gnu-gcc -I ~/ex_linux/065_arm/cpu_freq/buildroot/output/build/linux-headers-custom/include/ -I ~/ex_linux/09_buildroot/buildroot/output/build/linux-custom/arch/arm64/include/generated/ -I ~/ex_linux/065_arm/cpu_freq/buildroot/output/build/linux-headers-custom/include/linux -I ~/ex_linux/065_arm/cpu_freq/buildroot/output/build/linux-custom/arch/arm64/include -o cpufreq_mygovernor.o cpufreq_mygovernor.c

asm/rwonce.h: No such file or directory
/arch/arm/include

/arch/arm64/include/

asm/rwonce.h: No such file or directory

sudo apt-get install git gcc-arm-linux-gnueabihf make ncurses-dev build-essential