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multiple CPUs per app?

multiple CPUs per app?

Questions and Answers : Preferences : multiple CPUs per app?
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doug

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Message 59260 - Posted: 29 Dec 2018, 17:03:34 UTC

Hi,

I would like to know if it is possible to have CPDN apps use more than one CPU. My CPDN project folder doesn't contain an app_config.xml (as does, e.g., milkyway or cosmology). Some questions:

1) is it possible to create an app_config.xml for CPDN and have the project use it, in particular to assign more than one CPU to an app?

2) if so, is there any idea how much faster an app would be with, say, 2 CPUs instead of 1? I know it won't be twice as fast, but it might be, say, half-again faster.

2) if the above is possible, what are the correct app names to use in the file? For example, from my milkyway app_config.xml:

   <app_version>
      <app_name>milkyway_nbody</app_name>
      <plan_class>mt</plan_class>
      <avg_ncpus>2</avg_ncpus>
   </app_version>

Thanks.

Doug
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Les Bayliss
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Message 59261 - Posted: 29 Dec 2018, 17:54:49 UTC

No, it's not possible.
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Profile Dave Jackson
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Message 59281 - Posted: 1 Jan 2019, 6:50:23 UTC

No, it's not possible.


This question has been asked numerous times over the years. As I understand it, the reason that the use of multiple CPU's hasn't been pursued is that in the climate models, each computation is dependent on the value produced by the previous one. This may not completely preclude some gains by using multiple cores but would almost certainly make any gains insignificant to the processing power lost by not having all cores crunching different tasks.
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Questions and Answers : Preferences : multiple CPUs per app?

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