Global min reduction

[nfarabullini]

Addition of global_min reduction for nflat_gradp:

    def global_min(self, buffer: data_alloc.NDArray) -> state_utils.ScalarType:
        min_buffer_arr = self._xp.array([self._xp.min(buffer)])
        recv_buffer = self._xp.empty(1, dtype=buffer.dtype)
        self.props.comm.Allreduce(min_buffer_arr, recv_buffer, mpi4py.MPI.MIN)
        return recv_buffer.item()

[halungge]

Can you add in a similar way a max and mean to Reductions ? The mean we will need to compute mean_cell_area and edge_lengths in the geometry and a max is needed at least somewhere in new driver statistics

[halungge]

For its good so far except for the GPU sync question, where I don't know whether that is mandatory.

[halungge]

We should probably consider the stream synchronisation issue here for cupy arrays. See the example in the tutorial: https://mpi4py.readthedocs.io/en/stable/tutorial.html#gpu-aware-mpi-python-gpu-arrays
I did not test it on GPU, did you? I would at least leave an TODO here that this might become a problem. Also ask the HPC - MPI pros like @msimberg ...

[havogt]

I would add the sync with a link to the tutorial. Probably something like

        if hasattr(array_ns, "cuda"):
            array_ns.cuda.runtime.deviceSynchronize()

[nfarabullini]

cscs-ci run default

[github-actions]

Mandatory Tests

Please make sure you run these tests via comment before you merge!

• cscs-ci run default

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• cscs-ci run benchmark-bencher

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