[Openmp-commits] [PATCH] D51875: [OPENMP][NVPTX] Add support for lastprivates/reductions handling in SPMD constructs with lightweight runtime.

[Alexey Bataev via Phabricator via Openmp-commits]

ABataev added a comment.

In https://reviews.llvm.org/D51875#1229517, @Hahnfeld wrote:

> In https://reviews.llvm.org/D51875#1229506, @ABataev wrote:
>
> > In https://reviews.llvm.org/D51875#1229502, @Hahnfeld wrote:
> >
> > > In https://reviews.llvm.org/D51875#1229496, @ABataev wrote:
> > >
> > > > In https://reviews.llvm.org/D51875#1229491, @Hahnfeld wrote:
> > > >
> > > > > I really, really dislike adding even more global buffers. `4096 * 32 * 56` are another 7MiB that are not usable for applications. What's wrong with using the existing ones?
> > > > >
> > > > > Can you upload the CodeGen patch for reductions somewhere? I thought we need a global scratchpad buffer that is adressable for all teams?
> > > >
> > > >
> > > > I really, really dislike an implementation in ibm-devel, the scratchpad solution will never be added to the trunk. The existing ones cannot be reused, as they are allocated only if the full runtime is used.
> > >
> > >
> > > What's the overhead of initializing it? The whole `libomptarget-nvptx` is already a pretty much mess, see my thread on openmp-dev.
> >
> >
> > It is not the runtime issue, it is the problem with the compiler itself. It breaks compatibility with the other outlined regions and, thus, it cannot be committed to trunk.
>
>
> Can you please describe the problems? Again, maybe posting the patch may help.


I already described it - it breaks the compatibility with other outlined regions and breaks the whole design of the OpenMP implementation.

>> I'd like to have this at least as a temporirily solution to support lastprivates/reductions in SPMD mode with lightweight runtime. We can reduce the size of the preallocated buffers, if you wish.
> 
> Is that a commitment to actively work on that area?

Yes, Alex Eichenberger tries to invent something, that will allow us to use something similar to ibm-devel but without breaking the design of OpenMP in the compiler. But it requires some time. But I'd like to have something working, at least.


Repository:
  rOMP OpenMP

https://reviews.llvm.org/D51875