Dear all! using the split collective procedures MPI_File_write_all_begin() and MPI_File_write_all_end() causes some confusion to me. It was my intention to implement asynchronous file i/o using those procedures. The idea is to calculate some 'useful' stuff while writing tons of data to disk. Well, buffering the local arrays and replacing MPI_File_write_all() by MPI_File_write_all_begin() and MPI_File_write_all_end() wasn't that hard. However my expectations were not met: * No additional thread is spread out while writing * No benefit in runtime can be observed; The program simply waits as it did before. It just comes with the difference spending a lot of time calling MPI_File_write_all_end() instead of MPI_File_write_all(). It appears to me that MPI_File_write_begin() does not trigger the actual write command.
What I have is a iterative workflow where data shall be written to disk every 20th increment. So, what I want to achieve is writing to disk in the background while further 20 iterations are processed. I am coding a mixture of Fortran 90, F03, F08 and building with gfortran 4.7.1 and OpenMPI 1.6 . The environment in question is a quad-socket system equipped with E7-4860 running Debian Squeez. Unfortunately, I don't know about its i/o capabilities but it is nothing fancy. Do you have any idea what I have done wrong? Thanks in advance! Cheers, Stefan
