Hi folks I posted this to the devel list the other day, but it raised no responses. Maybe people will have more to say here.
Questions: How much does using the MPI wrappers influence the memory management at runtime? What has changed in this regard from 1.2.3 to 1.2.4? The reason I ask is that I have an f90 code that does very strange things. The structure of the code is not all that straightforward, with a "tree" of modules usually allocating their own storage (all with save applied globally within the module). Compiling with OpenMPI 1.2.4 coupled to a gcc 4.3.0 prerelease and running as a single process (with no explicit mpirun), the elements of one particular array seem to revert to previous values between where they are set and a later part of the code. (I'll refer to this as The Bug, and having the matrix elements stay as set as "expected behaviour".) The most obvious explanation would be a coding error. However, compiling and running this with OpenMPI 1.2.3 gives me the expected behaviour! As does compiling and running with a different MPI implementation and compiler set. Replacing the prerelease gcc 4.3.0 with the released 4.2.2 makes no change. The Bug is unstable. Removing calls to various routines in used modules (that otherwise do not effect the results) returns to expected behaviour at runtime. Removing a call to MPI_Recv that is never called returns to expected behaviour. Because of this I can't reduce the problem to a small testcase, and so have not included any code at this stage. If I run the code with mpirun -np 1 the problem goes away. So one could presumably simply say "always run it with mpirun." But if this is required, why does OpenMPI not detect it? And why the difference between 1.2.3 and 1.2.4? Does anyone care to comment? Ciao Terry -- Dr Terry Frankcombe Physical Chemistry, Department of Chemistry Göteborgs Universitet SE-412 96 Göteborg Sweden Ph: +46 76 224 0887 Skype: terry.frankcombe <te...@chem.gu.se>
