[Darshan-users] Question regarding Job Summary report

[Rob Latham]

On Tue, May 03, 2011 at 10:21:38AM -0700, Hedges, Richard M. wrote:
> I've been using the Darshan software to analyze I/O for a variety of user
> codes here at LLNL.  On the second page there are a set of plots labelled
> "Timespan from first to last ...."  I believe that I understand what they
> are representing, but I am at a loss to understand what issue it is that
> they are trying to reveal ... So maybe I don't get what they are.  Could
> someone explain to me what these are and what problem they are being applied
> to?

Hi Richard.  Those plots help us understand if an application opens
and closes files frequently through the run, or if it opens a file (or
files) once and keeps it open for the entire run.

Darshan keeps open and close timestamps for the file (and I think also
the first/last read/write operations), but does not timestamp
individual operations, so we still don't entirely know from those
plots when reads and writes occur.  Still, those charts can help a
little when we know nothing about the application.  At least they have
us asking the right questions of the scientists.

==rob

-- 
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA