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Thread: cpuid+rdtsc

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  1. 10-10-2007, 07:12 AM #1
    DrLecter
    DrLecter is offline Junior Member
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    Question cpuid+rdtsc

    How can I learn about the number of cycles a processor instruction takes to execute?
    Nor AMD not Intel gives that kind of information and RDTSC is not a precise any more.
    Any hint will be welcome?
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  2. 10-10-2007, 08:22 AM #2
    mlau
    mlau is offline Senior Member
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    Quote Originally Posted by DrLecter View Post
    How can I learn about the number of cycles a processor instruction takes to execute?
    Nor AMD not Intel gives that kind of information and RDTSC is not a precise any more.
    Any hint will be welcome?
    Well, take readings of the TSC before and after the
    instruction you want to measure. Make sure you disable
    all IRQs and run this under a single-task OS like DOS.
    Since DOS does not know of SMP and SpeedStep, the
    TSC should be very reliable, and noone will reschedule
    your app.
    Last edited by mlau; 10-10-2007 at 08:24 AM.
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