[gmx-developers] discussion of deprecation announcements in GROMACS 2021

[Mark Abraham]

Hi,

The developers announce functionality as deprecated each year. That gives
users a chance to learn what changes may happen in future, so they can plan
how to adapt.

I've proposed several things to deprecate at
https://gitlab.com/gromacs/gromacs/-/issues/3818 and want to encourage
people to consider those choices before I make an MR for the GROMACS 2021
release notes.

Often things we announce as deprecated remain that way for months or years
before we actually remove it. That's fine.

The potentially controversial item is the proposed deprecation of OpenCL
support. We have active funded projects to implement support with SYCL for
Intel GPUs, and some as-yet undecided framework for AMD GPUs. When those
are in place, the usefulness of OpenCL as a portable approach for GPU
support in GROMACS has expired. We have not had the resources to develop
the current CUDA and OpenCL GPU code forks to the same extent, and we are
not going to be able to do that any better when SYCL and perhaps HIP are
also around. Continuing to support and test the OpenCL functionality is
work that we would need to do that costs us the opportunity to further
improve the ports we expect users to be using in GROMACS 2022.

So, when we have made enough progress on the Intel and AMD fronts, we want
the freedom to remove the OpenCL port, so that there's less work for us to
do and more freedom to adapt our GPU portability layer in the directions it
needs to move. I hope that will happen some time during the 2021 calendar
year, but it won't be January :-).

Please feel free to discuss OpenCL here, and anything else at that gitlab
issue!

Mark
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