Microsecond accurate (or better) process timing in Linux

Question

I need a very accurate way to time parts of my program. I could use the regular high-resolution clock for this, but that will return wallclock time, which is not what I need: I needthe time spent running only my process.

I distinctly remember seeing a Linux kernel patch that would allow me to time my processes to nanosecond accuracy, except I forgot to bookmark it and I forgot the name of the patch as well :(.

I remember how it works though:

On every context switch, it will read out the value of a high-resolution clock, and add the delta of the last two values to the process time of the running process. This produces a high-resolution accurate view of the process' actual process time.

The regular process time is kept using the regular clock, which is I believe millisecond accurate (1000Hz), which is much too large for my purposes.

Does anyone know what kernel patch I'm talking about? I also remember it was like a word with a letter before or after it -- something like 'rtimer' or something, but I don't remember exactly.

(Other suggestions are welcome too)

---

The Completely Fair Scheduler suggested suggested by Marko is not what I was looking for, but it looks promising. The problem I have with it is that the calls I can use to get process time are still not returning values that are granular enough.

• times() is returning values 21, 22, in milliseconds.
• clock() is returning values 21000, 22000, same granularity.
• getrusage() is returning values like 210002, 22001 (and somesuch), they look to have a bit better accuracy but the values look conspicuously the same.

So now the problem I'm probably having is that the kernel has the information I need, I just don't know the system call that will return it.

Answer 1

If you are looking for this level of timing resolution, you are probably trying to do some micro-optimization. If that's the case, you should look at PAPI. Not only does it provide both wall-clock and virtual (process only) timing information, it also provides access to CPU event counters, which can be indispensable when you are trying to improve performance.

http://icl.cs.utk.edu/papi/