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I was wondering how to calculate the total CPU usage of a process.

If I do cat /proc/pid/stat, I think the relevant fields are (taken from lindevdoc.org):

  1. CPU time spent in user code, measured in jiffies
  2. CPU time spent in kernel code, measured in jiffies
  3. CPU time spent in user code, including time from children
  4. CPU time spent in kernel code, including time from children

So is the total time spend the sum of fields 14 to 17?

6 Answers 6

180

Preparation

To calculate CPU usage for a specific process you'll need the following:

  1. /proc/uptime
    • #1 uptime of the system (seconds)
  2. /proc/[PID]/stat
    • #14 utime - CPU time spent in user code, measured in clock ticks
    • #15 stime - CPU time spent in kernel code, measured in clock ticks
    • #16 cutime - Waited-for children's CPU time spent in user code (in clock ticks)
    • #17 cstime - Waited-for children's CPU time spent in kernel code (in clock ticks)
    • #22 starttime - Time when the process started, measured in clock ticks
  3. Hertz (number of clock ticks per second) of your system.

Calculation

First we determine the total time spent for the process:

total_time = utime + stime 

We also have to decide whether we want to include the time from children processes. If we do, then we add those values to total_time:

total_time = total_time + cutime + cstime 

Next we get the total elapsed time in seconds since the process started:

seconds = uptime - (starttime / Hertz) 

Finally we calculate the CPU usage percentage:

cpu_usage = 100 * ((total_time / Hertz) / seconds) 

See also

Top and ps not showing the same cpu result

How to get total cpu usage in Linux (c++)

Calculating CPU usage of a process in Linux

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19 Comments

Hi, this would give the avg cpu usage since the application start. If a process has in last 5 secs consumed most of cpu while it was idle for 1hr, this code would still give the avg value since its uptime.. Right
Yes, this is average cpu usage since the process started (starttime). So the hour the process spent idle is also factored into the calculation (uptime - starttime).
How to get this value in android? I believe CLK_TCK is not giving HZ?
I got it from the same link Thanks :). I have posted an answer to my question please check it
@T-D The uptime I use in the equation is the first parameter of /proc/uptime. I mentioned the second parameter of /proc/uptime to indicate how to calculate the total CPU usage of the system as a whole rather than a single process; since we are only concerned with the CPU usage of a single process, the second parameter is unused in the equations.
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6

Yes, you can say so. You can convert those values into seconds using formula:

 sec = jiffies / HZ ; here - HZ = number of ticks per second 

HZ value is configurable - done at kernel configuration time.

Comments

6

Here is my simple solution written in BASH. It is a linux/unix system monitor and process manager through procfs, like "top" or "ps". There is two versions simple monochrome(fast) and colored version(little bit slow, but useful especially for monitoring the statе of processes). I made sorting by CPU usage.

https://github.com/AraKhachatryan/top

  • utime, stime, cutime, cstime, starttime used for getting cpu usage and obtained from /proc/[pid]/stat file.

  • state, ppid, priority, nice, num_threads parameters obtained also from /proc/[pid]/stat file.

  • resident and data_and_stack parameters used for getting memory usage and obtained from /proc/[pid]/statm file.

 function my_ps { pid_array=`ls /proc | grep -E '^[0-9]+$'` clock_ticks=$(getconf CLK_TCK) total_memory=$( grep -Po '(?<=MemTotal:\s{8})(\d+)' /proc/meminfo ) cat /dev/null > .data.ps for pid in $pid_array do if [ -r /proc/$pid/stat ] then stat_array=( `sed -E 's/(\([^\s)]+)\s([^)]+\))/\1_\2/g' /proc/$pid/stat` ) uptime_array=( `cat /proc/uptime` ) statm_array=( `cat /proc/$pid/statm` ) comm=( `grep -Po '^[^\s\/]+' /proc/$pid/comm` ) user_id=$( grep -Po '(?<=Uid:\s)(\d+)' /proc/$pid/status ) user=$( id -nu $user_id ) uptime=${uptime_array[0]} state=${stat_array[2]} ppid=${stat_array[3]} priority=${stat_array[17]} nice=${stat_array[18]} utime=${stat_array[13]} stime=${stat_array[14]} cutime=${stat_array[15]} cstime=${stat_array[16]} num_threads=${stat_array[19]} starttime=${stat_array[21]} total_time=$(( $utime + $stime )) #add $cstime - CPU time spent in user and kernel code ( can olso add $cutime - CPU time spent in user code ) total_time=$(( $total_time + $cstime )) seconds=$( awk 'BEGIN {print ( '$uptime' - ('$starttime' / '$clock_ticks') )}' ) cpu_usage=$( awk 'BEGIN {print ( 100 * (('$total_time' / '$clock_ticks') / '$seconds') )}' ) resident=${statm_array[1]} data_and_stack=${statm_array[5]} memory_usage=$( awk 'BEGIN {print( (('$resident' + '$data_and_stack' ) * 100) / '$total_memory' )}' ) printf "%-6d %-6d %-10s %-4d %-5d %-4s %-4u %-7.2f %-7.2f %-18s\n" $pid $ppid $user $priority $nice $state $num_threads $memory_usage $cpu_usage $comm >> .data.ps fi done clear printf "\e[30;107m%-6s %-6s %-10s %-4s %-3s %-6s %-4s %-7s %-7s %-18s\e[0m\n" "PID" "PPID" "USER" "PR" "NI" "STATE" "THR" "%MEM" "%CPU" "COMMAND" sort -nr -k9 .data.ps | head -$1 read_options } 

screenshot of working script

Comments

2

If need to calculate how much cpu% used by a process in last 10 secs

  1. get total_time (13+14) in jiffies => t1 starttime(22) in jiffies => s1

--delay of 10 secs

total_time (13+14) in jiffies => t2 starttime(22) in jiffies => s2

t2-t1 *100 / s2 - s1 wouldnt give the % ??

6 Comments

To get the CPU usage over an elapsed period of time (e.g. 10 seconds), you divide the elapsed process time by the total elapsed time.
s2-s1 wont be equal to 10 secs ?
@VilhelmGray what do u think?
I may be misinterpreting your equation, but if you're using starttime(22) then both s2 and s1 will be the same. starttime is the moment in time when the process was started, so the value stays the same throughout the life of your process.
oh oops. My mixup, i was assuming it to be time since it was started.
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2

Here is another way that I got my App's CPU usage. I did this in Android, and it makes a kernel top call and gets the CPU usage for your apps PID using what top returns.

public void myWonderfulApp() { // Some wonderfully written code here Integer lMyProcessID = android.os.Process.myPid(); int lMyCPUUsage = getAppCPUUsage( lMyProcessID ); // More magic } // Alternate way that I switched to. I found the first version was slower // this version only returns a single line for the app, so far less parsing // and processing. public static float getTotalCPUUsage2() { try { // read global stats file for total CPU BufferedReader reader = new BufferedReader(new FileReader("/proc/stat")); String[] sa = reader.readLine().split("[ ]+", 9); long work = Long.parseLong(sa[1]) + Long.parseLong(sa[2]) + Long.parseLong(sa[3]); long total = work + Long.parseLong(sa[4]) + Long.parseLong(sa[5]) + Long.parseLong(sa[6]) + Long.parseLong(sa[7]); reader.close(); // calculate and convert to percentage return restrictPercentage(work * 100 / (float) total); } catch (Exception ex) { Logger.e(Constants.TAG, "Unable to get Total CPU usage"); } // if there was an issue, just return 0 return 0; } // This is an alternate way, but it takes the entire output of // top, so there is a fair bit of parsing. public static int getAppCPUUsage( Integer aAppPID) { int lReturn = 0; // make sure a valid pid was passed if ( null == aAppPID && aAppPID > 0) { return lReturn; } try { // Make a call to top so we have all the processes CPU Process lTopProcess = Runtime.getRuntime().exec("top"); BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(lTopProcess.getInputStream())); String lLine; // While we have stuff to read and we have not found our PID, process the lines while ( (lLine = bufferedReader.readLine()) != null ) { // Split on 4, the CPU % is the 3rd field . // NOTE: We trim because sometimes we had the first field in the split be a "". String[] lSplit = lLine.trim().split("[ ]+", 4); // Don't even bother if we don't have at least the 4 if ( lSplit.length > 3 ) { // Make sure we can handle if we can't parse the int try { // On the line that is our process, field 0 is a PID Integer lCurrentPID = Integer.parseInt(lSplit[0]); // Did we find our process? if (aAppPID.equals(lCurrentPID)) { // This is us, strip off the % and return it String lCPU = lSplit[2].replace("%", ""); lReturn = Integer.parseInt(lCPU); break; } } catch( NumberFormatException e ) { // No op. We expect this when it's not a PID line } } } bufferedReader.close(); lTopProcess.destroy(); // Cleanup the process, otherwise you make a nice hand warmer out of your device } catch( IOException ex ) { // Log bad stuff happened } catch (Exception ex) { // Log bad stuff happened } // if there was an issue, just return 0 return lReturn; } 

4 Comments

I'd like to add that this has shown at times to not be a fast operation. I have seen this take 3+ seconds. I recently switched to the other answer I provided. Not blazing fast, but processes less lines. You only get back a single line for the PID you requested..
"I have seen this take 3+ seconds" => This is perfectly expected, the default top delay is 3s exactly, you can use -d 0 to avoid it and get an immediate result.
getTotalCPUUsage2 gets average cpu usage since bootup since /proc/stat returns values aggregated since the device booted
To calculate instantaneous, perform the operation twice and calculate the delta of /proc/stat values and calculate cpu usage from that delta.
-4

Here's what you're looking for:

//USER_HZ detection, from openssl code #ifndef HZ # if defined(_SC_CLK_TCK) \ && (!defined(OPENSSL_SYS_VMS) || __CTRL_VER >= 70000000) # define HZ ((double)sysconf(_SC_CLK_TCK)) # else # ifndef CLK_TCK # ifndef _BSD_CLK_TCK_ /* FreeBSD hack */ # define HZ 100.0 # else /* _BSD_CLK_TCK_ */ # define HZ ((double)_BSD_CLK_TCK_) # endif # else /* CLK_TCK */ # define HZ ((double)CLK_TCK) # endif # endif #endif 

This code is actually from cpulimit, but uses openssl snippets.

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