On Reducing I/O Overheads in Large-Scale Invariant Subspace Projections
Obtaining highly accurate predictions on properties of light atomic nuclei using the Configuration Interaction (CI) method requires computing the lowest eigenvalues and associated eigenvectors of a large many-body nuclear Hamiltonian, H. One particular approach, the J-scheme, requires the projection of the H matrix into an invariant subspace. Since the matrices can be very large, enormous computing power is needed while significant stresses are put on the memory and I/O sub-systems. By exploiting the inherent localities in the problem and making use of the MPI one-sided communication routines backed by RDMA operations available in the new parallel architectures, we show that it is possible to reduce the I/O overheads drastically for large problems. This is demonstrated in the subspace projection phase of J-scheme calculations on 6Li nucleus, where our new implementation based on one-sided MPI communications outperforms the previous I/O based implementation by almost a factor of 10.
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