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EPCCed / gpu-directives

Contains material for a course using GPU directives
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simd directives #6

Open lucaparisi91 opened 4 months ago

lucaparisi91 commented 4 months ago

What does #pragma omp simd actually do on the GPU ?

lucaparisi91 commented 4 months ago

NVidia GPUs can have vectorized instructions of length 2 or 4 . This is different from SIMT parallelism. The instruction will operate on 2(4) x 32 threads in a warp .
It looks like some old versions of CCE interprets simd as simt , and the value is required to use all threads in a warp. That is not the case for new versions of cce . At the moment most compilers seem to ignore the simd directive.