On Tue, 10 Jul 2007, Brian Biskeborn wrote: > > Hello, > > Does anyone here have experience with using Petsc on a Blue Gene system? > I'm at IBM's Almaden Research Center and am currently involved in porting > some code that uses Petsc to Blue Gene. I've managed to compile and run > the code, and it seems to produce the correct results, but it generates > many floating point alignment exceptions at runtime.
Can you send a log of these messages? Is this on BGL or BGP? Does the program abort? [on encountering these messages] With the minimal runs I've done on BGL - I don't remember seing any such messages. > I traced some of these warnings to a call to MatAssemblyBegin, so > I'm thinking maybe the problem is in Petsc. The Blue Gene > architecture requires 8- or 16-byte memory alignment for floating > point operations, depending on whether they are issued in parallel, > so I tried bumping up the alignment value in > src/sys/src/memory/mal.c. This had no effect on the problem. [Barry can confirm this] the code in mal.c attempts to make sure the memory allocated by PETSc is aligned properly. [8 byte boundary for doubles] One possibility is that the data passed in to MatAssemblyBegin() is not aligned? Satish > I didn't write any of the code I'm porting, and I'm not too familiar with > it yet, so I suppose the problem could really be anywhere. My question > here is simply this: has anyone seen this problem? Does it sound like an > issue with Petsc, or is it more likely to be in the top-level code? > > Thanks, and best regards, > Brian > >
