GPGPUs

[luminousone]

On Friday, 16 August 2013 at 20:07:32 UTC, John Colvin wrote:
> We have a[] = b[] * c[] - 5; etc. which could work very neatly 
> perhaps?

While this in fact could work, given the nature of GPGPU it would
not be very effective.

In a non shared memory and non cache coherent setup, the entirety
of all 3 arrays have to be copied into GPU memory, had that
statement ran as gpu bytecode, and then copied back to complete
the operation.

GPGPU doesn't make sense on small code blocks, both in
instruction count, and by how memory bound a particular statement
would be.

The compiler needs to either be explicitly told what can/should
be ran as a GPU function, or have some intelligence about what to
or not to run as a GPU function.

This will get better in the future, APU's using the full HSA
implementation will drastically reduce the "buyin" latency/cycle
cost of using a GPGPU function, and make them more practical for
smaller(in instruction count/memory boundess) operations.