Accurate calculation of CPU usage given in percentage in Linux?

According the htop source code, my assumptions looks like they are valid:

(see static inline double LinuxProcessList_scanCPUTime(LinuxProcessList* this) function at LinuxProcessList.c)

// Guest time is already accounted in usertimeusertime = usertime - guest;                             # As you see here, it subtracts guest from user timenicetime = nicetime - guestnice;                         # and guest_nice from nice time// Fields existing on kernels >= 2.6// (and RHEL's patched kernel 2.4...)unsigned long long int idlealltime = idletime + ioWait;  # ioWait is added in the idleTimeunsigned long long int systemalltime = systemtime + irq + softIrq;unsigned long long int virtalltime = guest + guestnice;unsigned long long int totaltime = usertime + nicetime + systemalltime + idlealltime + steal + virtalltime;

And so, from fields listed in the first line of /proc/stat: (see section 1.8 at documentation)

     user    nice   system  idle      iowait irq   softirq  steal  guest  guest_nicecpu  74608   2520   24433   1117073   6176   4054  0        0      0      0

Algorithmically, we can calculate the CPU usage percentage like:

PrevIdle = previdle + previowaitIdle = idle + iowaitPrevNonIdle = prevuser + prevnice + prevsystem + previrq + prevsoftirq + prevstealNonIdle = user + nice + system + irq + softirq + stealPrevTotal = PrevIdle + PrevNonIdleTotal = Idle + NonIdle# differentiate: actual value minus the previous onetotald = Total - PrevTotalidled = Idle - PrevIdleCPU_Percentage = (totald - idled)/totald

The following is a bash script which is based on Vangelis's answer. It produces output like this:

total 49.1803cpu0 14.2857cpu1 100cpu2 28.5714cpu3 100cpu4 30cpu5 25

Create a file called get_cpu_usage.sh

Run it using the following command: bash get_cpu_usage.sh 0.2

The argument is the number of seconds to measure. In this case it's 200 milliseconds.

The contents are:

#!/bin/shsleepDurationSeconds=$1previousDate=$(date +%s%N | cut -b1-13)previousStats=$(cat /proc/stat)sleep $sleepDurationSecondscurrentDate=$(date +%s%N | cut -b1-13)currentStats=$(cat /proc/stat)    cpus=$(echo "$currentStats" | grep -P 'cpu' | awk -F " " '{print $1}')for cpu in $cpusdo    currentLine=$(echo "$currentStats" | grep "$cpu ")    user=$(echo "$currentLine" | awk -F " " '{print $2}')    nice=$(echo "$currentLine" | awk -F " " '{print $3}')    system=$(echo "$currentLine" | awk -F " " '{print $4}')    idle=$(echo "$currentLine" | awk -F " " '{print $5}')    iowait=$(echo "$currentLine" | awk -F " " '{print $6}')    irq=$(echo "$currentLine" | awk -F " " '{print $7}')    softirq=$(echo "$currentLine" | awk -F " " '{print $8}')    steal=$(echo "$currentLine" | awk -F " " '{print $9}')    guest=$(echo "$currentLine" | awk -F " " '{print $10}')    guest_nice=$(echo "$currentLine" | awk -F " " '{print $11}')    previousLine=$(echo "$previousStats" | grep "$cpu ")    prevuser=$(echo "$previousLine" | awk -F " " '{print $2}')    prevnice=$(echo "$previousLine" | awk -F " " '{print $3}')    prevsystem=$(echo "$previousLine" | awk -F " " '{print $4}')    previdle=$(echo "$previousLine" | awk -F " " '{print $5}')    previowait=$(echo "$previousLine" | awk -F " " '{print $6}')    previrq=$(echo "$previousLine" | awk -F " " '{print $7}')    prevsoftirq=$(echo "$previousLine" | awk -F " " '{print $8}')    prevsteal=$(echo "$previousLine" | awk -F " " '{print $9}')    prevguest=$(echo "$previousLine" | awk -F " " '{print $10}')    prevguest_nice=$(echo "$previousLine" | awk -F " " '{print $11}')        PrevIdle=$((previdle + previowait))    Idle=$((idle + iowait))    PrevNonIdle=$((prevuser + prevnice + prevsystem + previrq + prevsoftirq + prevsteal))    NonIdle=$((user + nice + system + irq + softirq + steal))    PrevTotal=$((PrevIdle + PrevNonIdle))    Total=$((Idle + NonIdle))    totald=$((Total - PrevTotal))    idled=$((Idle - PrevIdle))    CPU_Percentage=$(awk "BEGIN {print ($totald - $idled)/$totald*100}")    if [[ "$cpu" == "cpu" ]]; then        echo "total "$CPU_Percentage    else        echo $cpu" "$CPU_Percentage    fidone

Hey i was also researching for the topic and found this thread really helpful. I used Vangelis Tasoulas formula to write a small python script for this. Attached is my Python code for the issue. It loads the cpu usage per cpu_id every second. Maybe its helps others as well. Also comments/suggestions are welcome :-)

#!/usr/bin/python # -*- coding: utf-8 -*-'''Created on 04.12.2014@author: plagtag'''from time import sleepimport sysclass GetCpuLoad(object):    '''    classdocs    '''    def __init__(self, percentage=True, sleeptime = 1):        '''        @parent class: GetCpuLoad        @date: 04.12.2014        @author: plagtag        @info:         @param:        @return: CPU load in percentage        '''        self.percentage = percentage        self.cpustat = '/proc/stat'        self.sep = ' '         self.sleeptime = sleeptime    def getcputime(self):        '''        http://stackoverflow.com/questions/23367857/accurate-calculation-of-cpu-usage-given-in-percentage-in-linux        read in cpu information from file        The meanings of the columns are as follows, from left to right:            0cpuid: number of cpu            1user: normal processes executing in user mode            2nice: niced processes executing in user mode            3system: processes executing in kernel mode            4idle: twiddling thumbs            5iowait: waiting for I/O to complete            6irq: servicing interrupts            7softirq: servicing softirqs        #the formulas from htop              user    nice   system  idle      iowait irq   softirq  steal  guest  guest_nice        cpu  74608   2520   24433   1117073   6176   4054  0        0      0      0        Idle=idle+iowait        NonIdle=user+nice+system+irq+softirq+steal        Total=Idle+NonIdle # first line of file for all cpus        CPU_Percentage=((Total-PrevTotal)-(Idle-PrevIdle))/(Total-PrevTotal)        '''        cpu_infos = {} #collect here the information        with open(self.cpustat,'r') as f_stat:            lines = [line.split(self.sep) for content in f_stat.readlines() for line in content.split('\n') if line.startswith('cpu')]            #compute for every cpu            for cpu_line in lines:                if '' in cpu_line: cpu_line.remove('')#remove empty elements                cpu_line = [cpu_line[0]]+[float(i) for i in cpu_line[1:]]#type casting                cpu_id,user,nice,system,idle,iowait,irq,softrig,steal,guest,guest_nice = cpu_line                Idle=idle+iowait                NonIdle=user+nice+system+irq+softrig+steal                Total=Idle+NonIdle                #update dictionionary                cpu_infos.update({cpu_id:{'total':Total,'idle':Idle}})            return cpu_infos    def getcpuload(self):        '''        CPU_Percentage=((Total-PrevTotal)-(Idle-PrevIdle))/(Total-PrevTotal)        '''        start = self.getcputime()        #wait a second        sleep(self.sleeptime)        stop = self.getcputime()        cpu_load = {}        for cpu in start:            Total = stop[cpu]['total']            PrevTotal = start[cpu]['total']            Idle = stop[cpu]['idle']            PrevIdle = start[cpu]['idle']            CPU_Percentage=((Total-PrevTotal)-(Idle-PrevIdle))/(Total-PrevTotal)*100            cpu_load.update({cpu: CPU_Percentage})        return cpu_loadif __name__=='__main__':    x = GetCpuLoad()    while True:        try:            data = x.getcpuload()            print data        except KeyboardInterrupt:            sys.exit("Finished")