
302 High Performance Parallel I/O
FIGURE 26.5: Steps required to improve performance of writes in HDF-based
MPI codes.
ftruncate optimization removed a POSIX ftruncate call from the HDF
code, which caused negligible problems at smaller concurrencies but quickly
became a bottleneck in the neighborhood of 1024 tasks. In general, the nature
of the optimizations is to re-organize the I/O into forms that match the file
system’s optimal block size and to align file offsets along those blocks.
26.2.2 MADBENCH and File System Health
I/O performance is a characteristic of applications and the shared resources
on which the applications run. In some cases, “out”