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Do you use CAF? and if so, do you oversubscribe the cpu cores?

Ron_Green
Moderator
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If you are using Coarray Fortran I am curious about your usage.  So I'm interested in your DESIGN and PROTOTYPING phase, not production runs:

When you prototype or write new code using CAF,  and when you run your CAF code do you "oversubscribe"?  As an example, if you have a 4-core system do you run more than 4 CAF images on your workstation or server? 


as another example and question, if you have hyper-threading enabled - a 4 core system with HT has 8 logical processors.  Do you run 4 images or 8 images?

Same example, would you ever run 9 more or more images knowing that your #images exceeds your #logical processors?

Obviously for performance you want images mapped to unique cores so that there is no communication delays in moving data (this is obvious isn't it??).

Is oversubscribing more images than logical processors something that you do often, or you would ever expect to do on a regular basis?

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JAlexiou
New Contributor I
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I turn off HT and always undersubscribe the images. On a 6 core machine, I run 4 images. After some testing, it seems this yields me the best results. There is something magic about 4 images that make things click together nicely. I suppose if I had a 10 core machine I would use 8 images. Never a multiple of 3, or an odd number.

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