May 2015 – ROMIO

aggregation selection on Blue Gene

May 15, 2015 by Latham, Robert J.

For a lot of workloads, simply using collective I/O provides a big performance boost. Sometimes, though, it’s necessary to tune collective I/O a bit. The hint “cb_nodes” provides a way to select how many MPI processes will become aggregators. On Blue Gene, though, the story is a little more complicated. We’ll start with Blue Gene …

Non-blocking collective I/O

May 6, 2015 by Latham, Robert J.

The MPI standard defines non-blocking communication. It also defines non-blocking (independent) I/O. When it comes to collective I/O, the choices are blocking I/O or the little-developed and little-used “split collectives”. The HDF Group pushed to add true non-blocking collective I/O to the MPI standard. MPI-3.1 finally incorporates this feature. The use cases are motivated by …