Subj : Per thread cpu-usage on Linux
To   : comp.programming.threads
From : Christian Panten
Date : Wed Feb 16 2005 12:17 pm

Hi,

I have a problem to calculate the cpu time used by a thread...
The problem exists on several linux- and unix-systems.

First I try to describe what I want to calculate:
I work on a program which I have parallelized with pthreads. Now I want 
to calculate some times.
1. The running time of the whole programm: no problem: I use the real-timer.
2. The cpu running time of all threads: there is still a problem because 
there are varieties on several systems. But this is not the problem I 
want to discuss here.

3. My problem mow: I want to calculate the cpu-time of one thread (the 
thread is still running).
This I know:
Linux-kernel 2.4: I can calculate the cpu-time of a thread by using 
times(), because each thread seems to have its own counter.

Linux-kernel 2.6 with NPTL: The function times() returns the total 
cpu-time of the whole process. And I don't know how to get separate 
times for each thread.

I have made some trials:
- calculate the cpu-time with clock_gettime(CLOCK_THREAD_CPUTIME_ID, ..)
- reading the cpu-time from /proc/self/task/*ID*/stat
- calculate the cpu-time with clock_gettime(CLOCK_PROCESS_CPUTIME_ID, ..)

I wrote a test-program with 10 threads for a linux-server with 8 
processors. In doing so the times calculated with 
CLOCK_THREAD_CPUTIME_ID and CLOCK_PROCESS_CPUTIME_ID are nearly equal 
and the time read from /proc/... is in parts lower about several seconds 
as both cpu-timer, but not all the time.

Here one line from my test-program: (kernel 2.6)
thread:   6.470 read from /proc/...
cpu:     10.220 calculated with CLOCK_PROCESS_...
times:   72.420 calculated with times()
thread2: 10.219 calculated with CLOCK_THREAD_...

I hope you can help me...
1. Does anyone know how I can calculate the cpu-time of single thread? 
Reading the cpu time from /proc/... is not a satisfactory solution for me.
2. Does anyone know how I can solve the same problem with AIX 5.1?

Thx for your help...

Best regards
Christian

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