CPU Usage of a process
 

Hi guys,

I am currently writing a JAVA script to monitor certain unix processes through JConsole.

Upon having lots of trouble with runtime.exec, i decided to bypass the top/ps command call and just get the information straight from /proc/*pid*/whatever.

Now i can pull back any information from any of the files I want, and the current way i determine the CPU usage of a process is as follows:

Add the UTime and STime of that process from /proc/pid/stat then divide my pidCpu by UTime + STime + NTime from /proc/stat, then multiply that by 100, should give me the % cpu usage a process is using, right?

Theory being if I get the jiffies assigned to my process, I can divide that by the total jiffies the cpu assigns.

However, my results seem to vary from the ones gathered from top and ps. What am I doing wrong?

Any input is appreciated.

Every time you read a "file" from /proc, its value(s) are recalculated - at that point in time. So nothing ever correlates.
Same applies to "top" and "ps" BTW.

That means some (FSVO "some") variance is expected.

So the method of adding the Utime and Stime of a process, diving that by the Utime + Stime + Ntime of the /proc/stat file at that time and multiplying that by 100 should give you the %cpu that that process is using?