How to get stat information from a child process to measure resource utilization?

Question

I feel like this must have a simple answer, but I really don't know how to approach this.

For background, the stack of things is like this:

Python script -> C++ binary -(fork)-> actual thing we want to measure.

Essentially, we have a python script that simulates an environment by using tmp directories and running multiple instances of this network software stack we're developing. The script calls a host binary (which is unimportant here), and then, after it loads, a helper binary. The helper binary can be passed a parameter to daemonize, and when it does this, it forks in the usual way.

What we need to do is measure the daemon's CPU utilization, but I don't really know how to. What I have done is read the stat file periodically, but since the process daemonizes, I can't use echo $! to get its PID. Using ps aux | grep 'thing' ps aux | grep 'thing' works fine, but I think this is giving me the parent process, because the stat information looks like this:

1472582561 9455 (nlsr) S 1 9455 9455 0 -1 4218944 394 0 0 0 13 0 0 0 20 0 2 0 909820 184770560 3851 18446744073709551615 4194304 5318592 140734694817376 140734694810512 140084250723843 0 0 16781312 0 0 0 0 17 0 0 0 0 0 0 7416544 7421528 16224256 140734694825496 140734694825524 140734694825524 140734694825962 0

I know that the parent process should not be PID1, and definitely the utime field and similar should be greater than 13 clock ticks. This is what is leading me to conclude that this process is really the parent process, and not the forked child that's doing all the work.

I can modify pretty much any file necessary, but because of code review constraints, design specs., etc., the less I have to change along many files, the better.

Answer 1

1. Get the PID of the child reliably

   • fork() returns the PID of the child to the parent

2. Get the CPU stats from /proc/[PID]/stat

   • #14 utime - CPU time spent in user code, measured in clock ticks