Why is my computer not showing a speedup when I use parallel code?

Posted by Jared P on Stack Overflow See other posts from Stack Overflow or by Jared P
Published on 2010-03-08T23:01:08Z Indexed on 2010/03/08 23:06 UTC
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Filed under:

parallel

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openmp

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grand-central-dispatch

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speed-up

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c

So I realize this question sounds stupid (and yes I am using a dual core), but I have tried two different libraries (Grand Central Dispatch and OpenMP), and when using clock() to time the code with and without the lines that make it parallel, the speed is the same. (for the record they were both using their own form of parallel for). They report being run on different threads, but perhaps they are running on the same core? Is there any way to check? (Both libraries are for C, I'm uncomfortable at lower layers.) This is super weird. Any ideas?

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