The tool records information about I/O events that are triggered when the parallel application  accesses files. General statistics per file are calculated out of the events that are probed; for  example, the number of times each operation occurred and total time spent. Also, depending  on the event, it collects the following information: In particular, for read and write events, the tool can trace operations. For example, you can  access start offset, number of bytes, and end offset operations. To use MPI-IO, compile the application by using the  -g -Wl,--hash-style=sysv  -Wl,--emit-stub-syms  flags to prepare the binary file for instrumentation. You also can use hpctView to easily cycle instrumentation, execution, and visualization of  information that is implemented by MPI-IO tool. The tool abstracts the many environment  variables that can be used to control type and amount of information that is gathered. Figure 9-28 shows the hpctView visualization mode for data that is generated by using the  MPI-IO tool. More information about each I/O system call is provided on a per-task basis. Figure 9-28 hpctView: Message Passing Interface I/O tool profiling visualization GLYPH<SM590000> Total of bytes requested GLYPH<SM590000> Total of bytes delivered GLYPH<SM590000> Minimum requested size in bytes GLYPH<SM590000> Maximum requested size in bytes GLYPH<SM590000> Rate in bytes GLYPH<SM590000> Suspend wait count GLYPH<SM590000> Suspend wait time GLYPH<SM590000> Forward seeks average GLYPH<SM590000> Backward seeks average 302  IBM High-Performance Computing Insights with IBM Power System AC922 Clustered Solution 