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papercompute
Adept I
‎05-13-2015 03:47 AM

Is global synchronization in OpenCL possible?

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Hello everyone!

As well known OpenCL barrier() function works only for single workgroup, and there is no direct possibility to synchronize workgroups. If it possible what's best approach for global synchronization today? Using atomics, OpenCL 2.0 features, etc.?

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1 Solution
realhet
Miniboss
‎05-17-2015 05:45 AM

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Hi,

Yes, you should use atomics. As I know there is a special atomic instruction that use the faster GDS memory (atom_inc() vs. atomic_inc()), or maybe I know it wrong... Test both of then, anyways.

On GCN chips there is hardware global synchronization present. I've managed to synch 8 wavefronts/CU at 400KHz rate, so it's really fast, wasting only a few hundred cycles.

It's called Global Wave Synch (GWS). But unfortunately google can't find anything of it related to OpenCL.

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1 Reply
realhet
Miniboss
‎05-17-2015 05:45 AM

Jump to solution

Hi,

Yes, you should use atomics. As I know there is a special atomic instruction that use the faster GDS memory (atom_inc() vs. atomic_inc()), or maybe I know it wrong... Test both of then, anyways.

On GCN chips there is hardware global synchronization present. I've managed to synch 8 wavefronts/CU at 400KHz rate, so it's really fast, wasting only a few hundred cycles.

It's called Global Wave Synch (GWS). But unfortunately google can't find anything of it related to OpenCL.