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thesquiff
Journeyman III

4870X2

I've been using this card for development in the SDK1.3. I notice v1.4 now officially supports it.

I'm guessing I may actuallty have only been using only half the card before as I wasn't using multiple contexts. Are multiple contexts still required to use both gpus, or is this done automatically now? I've recompiled and can't see any performance increase.

 

TIA

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thesquiff
Journeyman III

Some hours of fiddling later and I have a program that creates a context on each device and launches the same kernels on the same data simultaneously. I was expecting the overall execution time to stay about the same + a bit of overhead. However the execution time has doubled....?

Presumably the kernels are not running concurrently as they should be. Do I need two monitors attached to the card or something (I seem to remember something about this mentioned before)?

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Any ideas anyone? I'm about to smash my head through the monitor...

Thanks

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May wasted hours later, I think I've found my problem. I needed to call calCtxIsEventDone() after calling the kernel for each GPU to allow the concurrency to occur. Seems like a messy trick - perhaps the multiGPU paragraph in the user guide could be expanded to mention this?

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