From: "Chaim B." <chaimbendelac@...>
Date: 2011-09-07T17:14:14+09:00
Subject: Re: /proc/PID/stat documentation?

A clarification:

There is a difference between forking a process, and spawning a thread 
(pthread library in C).

In the case of forked processes, the utime/stime represent the parent 
only. Once the forked processes die, their utime/stime are added to the 
cutime/cstime of the parent.

In the case of spawned threads however, the parent continues to 
accumulate utime/stime earned by its children, even if it is 
sleeping/waiting for its children to join. On a multi-processor system, 
these utime/stime parent counter increments will reflect the 
parallelism. In the case of spawned threads, the parent's cutime/cstime 
counters remain zero, even when the children die.

One most systems the "units" of time are 10 milisec. So a utime of 100 
represents one second of CPU time.

To understand the usage breakdown of the parent and children threads, it 
is necessary to go into the /proc/PID/task/ structure.

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