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

Guido Giuntoli guido.giuntoli at huawei.com
Thu Nov 26 10:45:06 CET 2020

Thanks a lot guys,

I am wondering where can I find this unity test, I want to run it also. Is it merged into the master?

Cheers, Guido.

From: gromacs.org_gmx-developers-bounces at maillist.sys.kth.se [mailto:gromacs.org_gmx-developers-bounces at maillist.sys.kth.se] On Behalf Of Erik Lindahl
Sent: Thursday, November 26, 2020 10:25 AM
To: gmx-developers at gromacs.org
Subject: Re: [gmx-developers] 4xN kernel using Advanced NEON (VL=128 bits) and double-FP

... and I ran through all the unit tests (which passed) on double precision ARM as recently as Tuesday ;-)



On Thu, Nov 26, 2020 at 10:23 AM Berk Hess <hess at kth.se<mailto:hess at kth.se>> wrote:

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



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

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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