content_image/1000976.jpg
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: 

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 

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. 

<img src='content_image/1000976.jpg'>

