For Frederic Rasio and his collaborators, tapping into the distributed power of Condor was relatively simple.
"Condor is probably best suited to 'embarrassingly parallel' codes; that is, programs in which each processor works independently," says Eric Ford, one of Rasio's students. "For example, we're doing Monte Carlo integrations in which we give each processor one test run at a time. Each processor does the same thing over and over again, but on slightly different initial conditions. Since there's no need for interprocessor communications while running any individual simulation, Condor works well."
Rasio and Ford originally wrote the two-planets-orbiting-a-star simulation on run-of-the-mill computer workstations in late 1995. In 1996, they ported the code to a parallel-processing IBM SP2 at the Cornell Theory Center at Cornell University.
Because the computer programs were originally written on workstations, the shift to Condor -- a network of workstations -- was straightforward. Similarly, Ford says, moving the code from the SP2 to Boston University's SGI Cray Origin2000, "was easy since both have Fortran compilers and support MPI (the Message Passing Interface, a set of computer libraries to handle parallel processing)."
Condor does not support MPI, but because the original code was written to work on workstations without MPI, those sections with MPI references were easily commented out.
"The only other difference is in one line of code which opens files," Ford says. The Fortran compilers on Condor and the Origin2000, he says, "seem to disagree on the proper call for opening a file."
According to Ford, the area that required the most work wasn't the actual computations, but rather the scripts that submit jobs to the computer and copy datafiles between magnetic tapes and disks.
"While both the Origin2000 and Condor have advantages and disadvantages, I've found the most significant differences to be in the human interaction rather than the computations or coding," Ford says. "For example, I find the Condor scheduling and transparent file handling preferable to the Origin2000's scheduler and multiple disks. On the down side, Condor requires installing software -- and upgrades -- on your own computer. This can take some time, especially if your system has a nonstandard configuration."
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