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iAndrei
Journeyman III

RV870: 20 SIMD engines (MPMD)

What means in architecture RV870 20 SIMD engines (MPMD)? 2 kernels OpenCL are simultaneously carried out?
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hazeman
Adept II

SIMDs are like cpus in normal computer. When you run OpenCL kernel each workgroup is placed in next available SIMD. So it doesn't mean that you can run 2 kernels. At the moment ATI doesn't support multiple kernels executions ( although it's rumored that RV8xx has hardware support for multiple kernels ).

 

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iAndrei
Journeyman III

What then means a slide 5 in presentation http://sa09.idav.ucdavis.edu/docs/SA09_AMD_IHV.pdf ?
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Slide 5 states the capabilities of SIMD. SIMD is specialized for highly parallel math computations, so it quite different architecture than classical CPU. Also terminology used by Nvidia/ATI is a little bit missleading for someone coming from CPU world ( GPU thread isn't the same as thread on CPU - the closest thing to CPU thread is warp which sometimes is called hardware thread ).

I propose to read documentation from CUDA ( which has better description of general concepts ), then ATI docs.

Also here http://www.beyond3d.com/content/reviews/53 , http://www.beyond3d.com/content/reviews/52 are quite detailed information about ATI's gpus architecture ( cache size, simd specs and more ).

 

 

 

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