如何在不使用 PSUtil 的情况下在 python 2.7 中获取 CPU 使用率

Question

试图在Python不使用PSUtil.

我已经尝试了以下但它似乎总是报告相同的数字......

def getCPUuse():
    return(str(os.popen("top -n1 | awk '/Cpu\(s\):/ {print $2}'").readline().strip(\
)))

print(getCPUuse())

即使我加载 CPU，这似乎总是报告 3.7%。

我也尝试了以下...

str(round(float(os.popen('''grep 'cpu ' /proc/stat | awk '{usage=($2+$4)*100/($2+$4+$5)} END {print usage }' ''').readline()),2))

这似乎总是返回 5.12。必须承认我真的不知道上面的内容是什么。如果我进入grep cpu /proc/stat命令行，我会得到这样的东西......

cpu  74429 1 19596 1704779 5567 0 284 0 0 0
cpu0 19596 0 4965 422508 1640 0 279 0 0 0
cpu1 18564 1 4793 427115 1420 0 1 0 0 0
cpu2 19020 0 4861 426916 1206 0 2 0 0 0
cpu3 17249 0 4977 428240 1301 0 2 0 0 0

我猜我的命令没有从上述输出中正确提取所有 CPU 内核的值？

我的目标是在不使用 PSUtil 的情况下从我的设备（Raspberry PI）获得总 CPU %。该图应反映操作系统任务管理器中显示的内容。

Answer 1

PSUtil、htop、mpstat 等所做的是读取以"cpu"（实际上是第一行） from开头的行/proc/stat，然后根据该行中的值计算百分比。您可以在man 5 proc（搜索“proc/stat”）中找到该行中值的含义。

这也是grep cpu /proc/stat | awk ....你提到的命令所做的。但是中的值/proc/stat代表自上次启动以来花费的时间！也许他们会在一段时间后回绕，我不确定，但关键是这些数字是在很长一段时间内测量的。

因此，如果您运行该命令，并在几秒钟（、几分钟甚至几小时）后再次运行它，它们将不会有太大变化！这就是为什么你看到它总是返回 5.12。

程序会top记住以前的值并从新读取的值中减去它们。根据结果​​，可以计算出实际反映最近 CPU 负载的“实时”百分比。

为了尽可能简单地在 python 中做类似的事情，但不运行外部命令来/proc/stat为我们读取和计算，我们可以将读取的值存储到文件中。下一次运行我们可以读回它们，并从新值中减去它们。

#!/usr/bin/env python2.7

import os.path

# Read first line from /proc/stat. It should start with "cpu"
# and contains times spent in various modes by all CPU's totalled.
#
with open("/proc/stat") as procfile:
    cpustats = procfile.readline().split()

# Sanity check
#
if cpustats[0] != 'cpu':
    raise ValueError("First line of /proc/stat not recognised")

#
# Refer to "man 5 proc" (search for /proc/stat) for information
# about which field means what.
#
# Here we do calculation as simple as possible:
# CPU% = 100 * time_doing_things / (time_doing_things + time_doing_nothing)
#

user_time = int(cpustats[1])    # time spent in user space
nice_time = int(cpustats[2])    # 'nice' time spent in user space
system_time = int(cpustats[3])  # time spent in kernel space

idle_time = int(cpustats[4])    # time spent idly
iowait_time = int(cpustats[5])    # time spent waiting is also doing nothing

time_doing_things = user_time + nice_time + system_time
time_doing_nothing = idle_time + iowait_time

# The times read from /proc/stat are total times, i.e. *all* times spent
# doing things and doing nothing since last boot.
#
# So to calculate  meaningful CPU % we need to know how much these values
# have *changed*.  So we store them in a file which we read next time the
# script is run.
# 
previous_values_file = "/tmp/prev.cpu"
prev_time_doing_things = 0
prev_time_doing_nothing = 0

try:
    with open(previous_values_file) as prev_file:
        prev1, prev2 = prev_file.readline().split()
    prev_time_doing_things = int(prev1)
    prev_time_doing_nothing = int(prev2)
except IOError:  # To prevent error/exception if file does not exist. We don't care.
    pass   

# Write the new values to the file to use next run
#
with open(previous_values_file, 'w') as prev_file:
    prev_file.write("{} {}\n".format(time_doing_things, time_doing_nothing))

# Calculate difference, i.e: how much the number have changed
#
diff_time_doing_things = time_doing_things - prev_time_doing_things
diff_time_doing_nothing = time_doing_nothing - prev_time_doing_nothing

# Calculate a percentage of change since last run:
#
cpu_percentage = 100.0 * diff_time_doing_things/ (diff_time_doing_things + diff_time_doing_nothing)

# Finally, output the result
#
print "CPU", cpu_percentage, "%"

这是一个与 不同的版本，它top每秒打印一次 CPU 使用率，记住以前在变量而不是文件中测量的 CPU 时间：

#!/usr/bin/env python2.7

import os.path
import time

def get_cpu_times():
    # Read first line from /proc/stat. It should start with "cpu"
    # and contains times spend in various modes by all CPU's totalled.
    #
    with open("/proc/stat") as procfile:
        cpustats = procfile.readline().split()

    # Sanity check
    #
    if cpustats[0] != 'cpu':
        raise ValueError("First line of /proc/stat not recognised")

    # Refer to "man 5 proc" (search for /proc/stat) for information
    # about which field means what.
    #
    # Here we do calculation as simple as possible:
    #
    # CPU% = 100 * time-doing-things / (time_doing_things + time_doing_nothing)
    #

    user_time = int(cpustats[1])    # time spent in user space
    nice_time = int(cpustats[2])    # 'nice' time spent in user space
    system_time = int(cpustats[3])  # time spent in kernel space

    idle_time = int(cpustats[4])    # time spent idly
    iowait_time = int(cpustats[5])    # time spent waiting is also doing nothing

    time_doing_things = user_time + nice_time + system_time
    time_doing_nothing = idle_time + iowait_time

    return time_doing_things, time_doing_nothing


def cpu_percentage_loop():
    prev_time_doing_things = 0
    prev_time_doing_nothing = 0
    while True:  # loop forever printing CPU usage percentage
        time_doing_things, time_doing_nothing = get_cpu_times()
        diff_time_doing_things = time_doing_things - prev_time_doing_things
        diff_time_doing_nothing = time_doing_nothing - prev_time_doing_nothing
        cpu_percentage = 100.0 * diff_time_doing_things/ (diff_time_doing_things + diff_time_doing_nothing)

        # remember current values to subtract next iteration of the loop
        #
        prev_time_doing_things = time_doing_things
        prev_time_doing_nothing = time_doing_nothing

        # Output latest perccentage
        #
        print "CPU", cpu_percentage, "%"

        # Loop delay
        #
        time.sleep(1)

if __name__ == "__main__":
    cpu_percentage_loop()