I am trying to make a program with C / C ++ to behave like a top command in Linux. I did some research and already knew how to count CPU usage as a process. We can get CPU usage by calculating stime + utime from / proc / [PID] / stat at the current time and after a few seconds. Then calculate the stime + utime differences and split the result with the uptime differences, then we get the percentage of CPU usage. It will be so simple in a single process / multithreading process.
The problem is how httpd is where it works as a multiprocessor. When the web server is busy, httpd will process child processes to serve a bunch of requests. Then I count the number of the total process, say 500. I want to calculate the CPU usage of these processes, but summarize them, so I only see 1 using httpd CPU. But if I execute the algorithm, as I mentioned above, when the number of processes decreases to <500 after a few seconds, I get negative values, since the calculation will be like this (for example, I choose a random number, just to give you a short description):
Uptime: 155123, No of processes : 500, Stime + Utime total of 500 processes : 3887481923874
Uptime: 155545, No of processes : 390, Stime + Utime total of 390 processes : 2887123343874
If you look at the example above, the Stime + Utime delta will result in a negative value, as the number of processes decreases and gives a lower value after a few milliseconds. I just want to know if there is a way to calculate a process like this? Thank.
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