Get a wrong cpu_frequence from raspberry pi in python

Question

i want use python to get the cpu_freq value from raspberry pi 4B

def GetCpuInfo():
    # Get CPU frequence
    cpu_freq =open("/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq").read()
    return cpu_freq

when i print the cpu_freq data, the output always fixed in 1800000(it's the max cpu frequence 1.8Ghz of raspberry pi),but when each time i use the

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq

this command in terminal,it give me the dynamic valve(600000-1800000) So why do i get wrong value when using the python? is it a wrong way to read this file?

Answer 1

There's nothing wrong with your read() .

The very act of starting Python can itself take enough cycles to cause the CPU to ramp up to full frequency, especially on a small system like a Pi.

To prevent that, add a delay to let it spool back down before you take your readings. For example:

import time

def GetCpuInfo():
    with open("/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq") as f:
        return f.read()

for _ in range(20):
    time.sleep(1)
    print(GetCpuInfo())