[gmx-users] Performance difference when using Gromacs 5.0 with different vector instructions

[MING HA]

Dear Mark,


Thanks for the quick response. So, in general, running using AVX
instructions will yield
better performance than SSE4.1?


Sincerely,
Ming

On Thu, Oct 19, 2017 at 5:18 PM, Mark Abraham <mark.j.abraham at gmail.com>
wrote:

> Hi,
>
> In short, yes. See
> http://manual.gromacs.org/documentation/2016.4/install-
> guide/index.html#simd-support.
> You should generally always use a GROMACS binary compiled for the highest
> SIMD level supported by your hardware. Your mdrun .log file will advise you
> when it observes that you are not.
>
> Mark
>
> On Thu, Oct 19, 2017 at 7:02 PM MING HA <mingtha at scarletmail.rutgers.edu>
> wrote:
>
> > Hi all,
> >
> >
> > I am running several resources using Gromacs 5.0 to run my simulations.
> > On some resources, Gromacs is compiled using SSE4.1 SIMD instructions,
> > while on others AVX_256 or AVX2_256 is used. While I don't find much of a
> > performance difference between AVX_256 and AVX2_256 instructions, there
> > is a large performance difference between resources that use SSE4.1 and
> > AVX instructions. Specifically, resources using SSE4.1 are about 2-3x
> > slower
> > than those that use AVX.
> >
> > I'm kind of new to the SIMD instructions used by Gromacs, so I was
> > wondering
> > whether the instruction set is causing the large performance difference.
> >
> >
> > Sincerely,
> > Ming
> > --
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