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I am using gprof to calculate the time spent during the execution of my program, for each function .

The last week I noticed that when CPU usage reached 100%, the program could not even start !

  • The code run for almost a day and nothing changed.
  • The CPU usage reaching 100% in some cases is inevitable and specially when I want to stress out my system and test the program while it uses the maximum amount of resources, with the help of the "stress" tool : http://weather.ou.edu/~apw/projects/stress/

I have read the thread :

Alternatives to gprof

and read the Mike Dunlavey's response :

What about problems that are not so localized? Do those not matter? Don't place expectations on gprof that were never claimed for it. It is only a measurement tool, and only of CPU-bound operations.

and also Norman Ramsey's response that had the high score :

Valgrind has an instruction-count profiler with a very nice visualizer called KCacheGrind. As Mike Dunlavey recommends, Valgrind counts the fraction of instructions for which a procedure is live on the stack, although I'm sorry to say it appears to become confused in the presence of mutual recursion. But the visualizer is very nice and light years ahead of gprof.

but as the thread is closed, as non constructive, I was wondering if this is the good direction to follow

Thanks in advance

P.S. While using google search, I didn't find something relevant when asking questions like

"why gprof doesn't work when cpu reach 100 %"

Thanks in advance

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user2307229
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1 Answers1

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All that 100% means is it's hung, and it's not doing I/O.

You're saying the program hangs when you run it with gprof, but not if you don't?

That's weird, but I wouldn't bother trying to figure it out.

As I've said over and over, I would just grab several stack samples manually. Then the percent of time used by any routine is just the fraction of samples it appears on, more or less. If you think you need high-precision measurements, try a stack-sampler like Zoom or OProfile.

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Mike Dunlavey
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  • Exactly, when I am not using gprof and CPU 100%, there is not even the first "welcome log printf" of my main printed.
    Also I have just installed **Oprofile** and I'll see what happens and keep you informed!     – user2307229 Jun 05 '13 at 13:46
  • @user2307229: It sounds like your program has an infinite loop when it starts. To find infinite loops, I just run it under GDB. In the output window, hit Control-C, to halt it. In the GDB window, do "thread 1" to make sure GDB is looking at your program's thread, and then type "bt" to show the call stack. Examine the code at each level of the stack, because the loop is on one of them. If it's still not obvious, single step it until you see it repeating itself. – Mike Dunlavey Jun 05 '13 at 15:16
  • Hi Mike, just finished testing my program with **oprofile** and runs pretty good! But I'll still do the debugging into gdb, cause there are some -also other- stuff that I must clarify. Again thanks a lot and I ll keep you updated ! – user2307229 Jun 07 '13 at 13:39