This astrophysical gas dynamics simulation was computationally intensive, consisting of over 3.5 million billion floating point operations and generating more than two terabytes of archived information. Until now we've only been able to model small patches near the surface of a star. Here we're modeling the whole star, and a rotating star no less. The simulation used two 64-processor systems interconnected by 100 megabyte per second HiPPI channels. For this simulation Porter, Anderson, and Habermann developed a new version of the LCSE's PPM gas dynamics code that employs a novel strategy for overcoming latency in parallel applications.
Latency refers to the time it takes to retrieve data from memory.
In large multiprocessor computing systems, such as the Origin2000, each group of processors that shares a common memory is simultaneously advancing a different portion of the problem. This means of attacking the problem in parallel is how the computer attains speed and efficiency. This communication between groups of processors introduces latency. The LCSE team's new PPM code prevents latency from slowing a computation because it overlaps the computation with the exchange of information among the other processor groups. Rather than eliminating latency, it hides it.