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

[Berk Hess]

Hi,

The kernels works fine in double precision with 128-bit SSE on x86.

Cheers,

Berk

On 2020-11-26 09:25, Guido Giuntoli wrote:
>
> 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 ;)
>
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