[gmx-developers] 4xN kernel using Advanced NEON (VL=128 bits) and double-FP

[Guido Giuntoli]

Hi,

I am building a minikernel of the 4 x N kernel and testing it in different architectures. Currently I am trying with in an ARMv8 with Advanced NEON using double-FP.

I see that this kernel operates with 4 particles at the time. When I use double-FP I can fill each SIMD unit with 2 FP numbers (128 bits long for Advanced NEON). I checked that that some interactions in this kernel between the 4 particles are not performed: particle 3 and 4 have net force = 0 (in this minikernel). Am I losing something here? Is the kernel prepared to operate in double precision for vector lengths of 128 bits? Is the masking mechanism intended to solve this issue?

Note: when I use single-FP the 4 forces are different from 0 as I expected.

Thanks a lot for the help ;)

Best regards | Mit freundlichen Grüßen

Guido Giuntoli

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