[gmx-users] Gromacs 2019.2 on Power9 + Volta GPUs (building and running)

[Mark Abraham]

Hi,

As with x86, GROMACS uses SIMD intrinsics on POWER9 and is thus fairly
insensitive to the compiler's vectorisation abilities. GCC is the only
compiler we've tested, as xlc can't compile simple C++11. As everywhere,
you should use the latest version of gcc, as IBM spent quite some years
landing improvements for POWER9.

EM is useless as a performance indicator of a dynamical simulation, avoid
that - it runs serial code much much more often.

Your run deliberately didn't fill the available cores, so just like on x86,
mdrun will leave the thread affinity handling to the environment, which is
often a path to bad performance. So, if you plan on doing that often,
you'll want to check out the mdrun performance guide docs about the mdrun
-pin and related options.

Mark


On Wed., 1 May 2019, 23:21 Alex, <nedomacho at gmail.com> wrote:

> Hi all,
>
> Our institution decided to be all fancy, so now we have a bunch of Power9
> nodes, each with 80 cores + 4 Volta GPUs. Stuff is managed by slurm. Today
> I did a simple EM ('gmx mdrun -ntomp 4 -ntmpi 4 -pme cpu -nb cpu') and the
> performance is abysmal, I would guess 100 times slower than on anything
> I've ever seen before.
>
> Our admin person emailed me the following:
> "-- it would not surprise me if the GCC compilers were relatively bad at
> taking advantage of POWER9 vectorization, they're likely optimized for
> x86_64 vector stuff like SSE and AVX operations.  This was an issue in the
> build, I selected "-DGMX_SIMD=IBM_VSX" for the config, but according to my
> notes, that was part of an attempt to fix the "unimplemented SIMD" error
> that was dogging me at first, and/but which was eventually cleared by
> switching to gcc-6."
>
> Does anyone have any comments/suggestions on building and running GMX on
> Power9?
>
> Thank you,
>
> Alex
> --
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