On Reducing I/O Overheads in Large-Scale Invariant Subspace Projections
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- Aktulga H.M., Yang C., Çatalyürek Ü.V., Maris P., Vary J.P., Ng E.G. (2012) On Reducing I/O Overheads in Large-Scale Invariant Subspace Projections. In: Alexander M. et al. (eds) Euro-Par 2011: Parallel Processing Workshops. Euro-Par 2011. Lecture Notes in Computer Science, vol 7155. Springer, Berlin, Heidelberg
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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