[gmx-users] importance of nvlink in GPU nodes?

[Szilárd Páll]

Note that while, as Mark said, GPU-to-GPU NVLink is not used optimized for,
when NVLink is the main CPU-to-GPU interconnect, GROMACS will certainly
transfer data across it! Currently only IBM Minsky systems have direct
CPU-to-GPU NVLink; on these transfers are ~3x faster than on PCI-E-based
systems. While transfers generally don't take much time, given that the
P100 GPUs are in general ~2.5x faster than previous generation, with PCI-E
the relative time spent in transfers will increase quite significantly.

So to answer the original question: the CPU-to-GPU NVLink can have a slight
impact on performance, but I'd expect that to be at most 10%, typically
less.

Cheers,
--
Szilárd

On Wed, Mar 29, 2017 at 2:46 PM, Mark Abraham <mark.j.abraham at gmail.com>
wrote:

> Hi,
>
> There's no use made of NVLINK in GROMACS. The 2018 release might make some
> use of it.
>
> Mark
>
> On Wed, Mar 29, 2017 at 4:19 AM Christopher Neale <
> chris.neale at alum.utoronto.ca> wrote:
>
> > Dear users:
> >
> > does anybody know if the presence of either CPU-to-GPU or GPU-to-GPU
> > nvlink affects the performance or efficiency of gromacs?
> >
> > Thank you,
> > Chris.
> > --
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