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    SubjectRe: Inconsistent timing results of multithreaded program on an SMP machine.

    Con Kolivas
    <kernel@kolivas.o To: Marcel Zalmanovici/Haifa/IBM@IBMIL
    rg> cc:, Muli Ben-Yehuda <>
    Subject: Re: Inconsistent timing results of multithreaded program on an SMP
    24/11/2005 11:40 machine.

    On Thu, 24 Nov 2005 19:33, Marcel Zalmanovici wrote:
    > Hi Con,
    > I've tried the pthread_join theory.
    > pthread_join completes very fast, no evidence on it being the perpetrator
    > here.
    > I've ran your ps -... idea in a different term window every ms while the
    > test was running. It created a large file so I won't mail it to you, but
    > both me and Muli observed that once the thread ends it quickly disappears
    > from the ps list.
    > I've also ran Muli's idea and added gettimeofday calls.
    > Here's the altered code and output:
    > (See attached file: idle.log)(See attached file: sched_test.c)
    > As you can see, if a thread already finished pthread_join returns in a
    > split second.
    > Any other ideas are welcome :-)

    Profile the actual application?

    Well, technically, this IS the actual application. Ultimately, I would like
    to make some changes to the kernel in order to reduce the cache misses and
    maybe improve run time as a consequence.
    Having results spread out as much as I get, it would be very difficult, if
    not impossible for me to estimate if my algorithm conveyed any real

    I have profiled (time ticks and L2 cache misses) the example I've posted
    and a few other variations on the example, but haven't seen nothing out of
    the ordinary.
    Around 98-99% of time and misses are at the inner loop of the example.

    Is there anything else I can check with profile that may help me understand
    the phenomenon ?

    > P.S. - I agree that Lotus isn't ideal for this kind of conversations, but
    > that's what IBM is using.

    It was tongue in cheek ;) Well that should still not stop you from replying

    below the original thread.


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