How to calculate the CPU usage of a process by PID

Question

I want to programmatically [in C] calculate CPU usage % for a given process ID in Linux.

How can we get the realtime CPU usage % for a given process?

To make it further clear:

• I should be able to determine the CPU usage for the provided processid or process.
• The process need not be the child process.
• I want the solution in 'C' language.

Answer 1

I think it's worth looking at GNU "time" command source code. time It outputs user/system cpu time along with real elapsed time. It calls wait3/wait4 system call (if available) and otherwise it calls times system call. wait* system call returns a "rusage" struct variable and times system call returns "tms". Also, you can have a look at getrusage system call which also return very interesting timing information. time

Answer 2

easy step to step for nubs like me :)

read the first line of /proc/stat to get total_cpu_usage1

sscanf(line,"%*s %llu %llu %llu %llu",&user,&nice,&system,&idle);
total_cpu_usage1 = user + nice + system + idle;

read /proc/pid/stat where pid is the pid of the process you want to know the cpu usage, like this:

sscanf(line,
"%*d %*s %*c %*d" //pid,command,state,ppid

"%*d %*d %*d %*d %*u %*lu %*lu %*lu %*lu"

"%lu %lu" //usertime,systemtime

"%*ld %*ld %*ld %*ld %*ld %*ld %*llu"

"%*lu", //virtual memory size in bytes
....)

now sum usertime and system time and get proc_times1

now wait 1 second or more

do it again, and get total_cpu_usage2 and proc_times2

the formula is:

(number of processors) * (proc_times2 - proc_times1) * 100 / (float) (total_cpu_usage2 - total_cpu_usage1)

you can get the num of cpus from /proc/cpuinfo

Answer 3

getrusage() can help you in determining the usage of current process or its child

Update: I can't remember an API. But all details will be in /proc/PID/stat, so if we could parse it, we can get the percentage.

EDIT: Since CPU % is not straight forward to calculate, You could use sampling kind of stuff here. Read ctime and utime for a PID at a point in time and read the same values again after 1 sec. Find the difference and divide by hundred. You will get utilization for that process for past one second.

(might get more complex if there are many processors)

Answer 4

Take a look at the "pidstat" command, sounds like exactly what you require.

Answer 5

Install psacct or acct package. Then use the sa command to display CPU time used for various commands. sa man page

A nice howto from the nixCraft site.

Answer 6

This is my solution...

/*
this program is looking for CPU,Memory,Procs also u can look glibtop header there was a lot of usefull function have fun..
systeminfo.c
*/
#include <stdio.h>
#include <glibtop.h>
#include <glibtop/cpu.h>
#include <glibtop/mem.h>
#include <glibtop/proclist.h>



int main(){

glibtop_init();

glibtop_cpu cpu;
glibtop_mem memory;
glibtop_proclist proclist;

glibtop_get_cpu (&cpu);
glibtop_get_mem(&memory);


printf("CPU TYPE INFORMATIONS \n\n"
"Cpu Total : %ld \n"
"Cpu User : %ld \n"
"Cpu Nice : %ld \n"
"Cpu Sys : %ld \n"
"Cpu Idle : %ld \n"
"Cpu Frequences : %ld \n",
(unsigned long)cpu.total,
(unsigned long)cpu.user,
(unsigned long)cpu.nice,
(unsigned long)cpu.sys,
(unsigned long)cpu.idle,
(unsigned long)cpu.frequency);

printf("\nMEMORY USING\n\n"
"Memory Total : %ld MB\n"
"Memory Used : %ld MB\n"
"Memory Free : %ld MB\n"
"Memory Buffered : %ld MB\n"
"Memory Cached : %ld MB\n"
"Memory user : %ld MB\n"
"Memory Locked : %ld MB\n",
(unsigned long)memory.total/(1024*1024),
(unsigned long)memory.used/(1024*1024),
(unsigned long)memory.free/(1024*1024),
(unsigned long)memory.shared/(1024*1024),
(unsigned long)memory.buffer/(1024*1024),
(unsigned long)memory.cached/(1024*1024),
(unsigned long)memory.user/(1024*1024),
(unsigned long)memory.locked/(1024*1024));

int which,arg;
glibtop_get_proclist(&proclist,which,arg);
printf("%ld\n%ld\n%ld\n",
(unsigned long)proclist.number,
(unsigned long)proclist.total,
(unsigned long)proclist.size);
return 0;
}

makefile is
CC=gcc
CFLAGS=-Wall -g
CLIBS=-lgtop-2.0 -lgtop_sysdeps-2.0 -lgtop_common-2.0

cpuinfo:cpu.c
$(CC) $(CFLAGS) systeminfo.c -o systeminfo $(CLIBS)
clean:
rm -f systeminfo