I just pushed some changes to MPICH master to help ROMIO deal with useful features that might not be available on all platforms and configurations. The system calls pread(2) and pwrite(2) act just like read(2) and write(2), but they take an additional offset parameter. The intent was to make life easier for threaded applications, but …
The fundamental data structure in ROMIO is the “flattened representation” of a dataype: this list of “offset-length” pairs describes any MPI datatype, if perhaps at the cost of memory and computational overhead. For years I have been linking in little utility functions to dump out these lists. Turns out GDB macros can do this for …
There are quite a few headaches when updating ROMIO and MPICH to be 64 bit clean. Once you’ve gone through all the hurdles to promote types and squash that last overflowing integer parameter, you are not done yet! Take a look at what happens on OS X (Darwin) when you pass 2147483648 (231) bytes to …
Let’s say you had a fat node with lots of memory, and you wanted to write 2 GiB of data out to a file with MPI-IO. How would you do that? You would naturally look at MPI_File_write() or one of its variants. This is the prototype for MPI_File_write_all: int MPI_File_write_all(MPI_File fh, const void *buf, int …