[Darshan-users] Estimating the overlap of MPI I/O wait time

[Jean-Thomas Acquaviva]

Hi,

I'm using Darshan to analyze the behavior of a parallel MPI Fortran application which writes to a shared file. Among 1024 MPI ranks only 48 are effectively doing I/O, this "geometry" is successfully reported by Darshan.

However, for the remaining 48 ranks Darshan reports the MPI I/O time spent writing to the shared file on a per rank basis, but I did not find a way to estimate the overlap between these different ranks.

At one end of the spectrum, if write accesses are serialized then the total I/O wait time for the application is the sum of the individual wait time of each rank.
On the other end, if write accesses are perfectly parallel the total app wait time is the max among the 48 writers.

Probably the exact number lies between these two values, is there a way to estimate it ?


Best regards,

 jean-thomas
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/darshan-users/attachments/20160203/cd185793/attachment.html>