In the second part of our interview with Michael Levine and Ralph Roskies, the two scientific co-directors at the Pittsburgh Supercomputing Center (PSC), they talk about the LeMieux computer, the PSC approach to supercomputing, and the challenges that lie ahead for the center. To read part one of the interview, where they talked extensively about the center's Cray XT3 system, go to http://www.hpcwire.com/hpc/686730.html.

HPCwire: LeMieux, your 3,000-processor six-teraflop HP system, which came into service in 2001, was the first NSF terascale system and for several years was the most powerful system available to NSF researchers. At soon-to-be five-years old, it's still one of the most used TeraGrid resources. What are your plans for this system and how much longer can it be useful?

Levine: It can be useful for a very long time. It's a question of how long it will continue to be cost effective. If Moore's Law holds, the amount of computing you can get from initial dollar capitalization keeps improving. On a monthly cost basis, this is a matter of maintenance costs. Likewise with the amount of computing per watt. Power is a large cost factor.

Roskies: At some point, it will no longer be cost effective and we will by then have transitioned the users to the XT3. No one will be left hanging.

Levine: Technically, LeMieux turned out to be a very good machine and continues to be a very good machine, very useful; it's not at a breaking point in any serious sense.

HPCwire: PSC has gained a reputation for its ability to take the leap with new technologies and transform them quickly into productive research tools. Going back to the CRAY Y-MP through half-a-dozen systems up to the XT3, you've received early, if not the first, models of new systems. What are the advantages of this approach? Are there disadvantages?

Roskies: The advantage is the payoff to the scientific community – because new machines will soon enough be sunsetted, as determined by the pace of technological development. So if you can get machines early in their cycle, it means you can use them longer. The earlier you get it, the more science you can get done in the useful lifetime of that machine.

Levine: Also, you bring that capability to the scientific community earlier. You could, of course, wait to introduce any new system into the open research community until it's more mature. But we can get productive use out of this early period, which means it's producing science that much sooner. And it allows us to have more influence with the vendors for the course of development of the system and its application to the NSF research community. This has certainly been the case for our involvement with the XT3 at the Sandia stage.

Roskies: The disadvantage is that there's more work by our systems staff than if we simply waited until the bugs get worked out. The machine would be better understood and it would be less effort to make it available. Of course, we're a major force in making it better understood, so not only are we improving things for our own users, we're improving it for everybody else's XT3 users. Somebody would have to discover these bugs. You can't avoid them.

A benefit to PSC is the cumulative aggregation of knowledge and experience that our staff gain in the process of birthing new systems, over and over, with various vendors and architectures.

Levine: This is a large amount of work, but there's a learning curve. We've learned a great deal about what to look for and how to go about this process, and we have designed our ancillary and support systems to be able to deal with a variety of machines.

For example, the scheduling software that users interact with to send jobs to the XT3 has features we need to make effective use of the machine. Essentially we're re-using technology that we've developed for earlier machines. We have to make it work with this architecture, but the effort of getting it going in the first place was substantial. The fact that we've done this before, that we've made the investment in education and training ourselves, puts us in a position where it makes good sense for us to be doing this work. For us to be doing this – doing the shakedown work with a new architecture and introducing it to the scientific community – is an efficient use of human resources.

HPCwire: Is there a “PSC” way of being a supercomputing center, and if so, what is it?

Roskies: To work with the TeraGrid, the scientific community, and the vendors to maximize scientific output. What we've discovered over the years is that to make this happen effectively entails working very closely with users, the researchers themselves, and it's certainly the case that an emphasis at PSC that has grown and evolved over time is for us to have a strong staff of people who work closely with our users to coordinate and optimize leading-edge applications, and who also contribute to improving the system's behavior.

HPCwire: TeraGrid last year embarked on its second five-year round of funding, this time – unlike the first – with the PSC as a major player. What is PSC's contribution?

Roskies: We are involved and actively participating in TeraGrid in a number of ways. First, we participate directly in overall direction. I'm on the executive steering committee for the Grid Infrastructure Group, the GIG. Michael is the principal contact for PSC as one of the eight resource-provider sites.

We also have a number of our key staff people committed heavily to TeraGrid work. Sergiu Sanielevici, our Director for Scientific Applications and User Support, is one of our most experienced computational scientists. He is now the TeraGrid area director for User Support. He oversees everything that has to do with coordinating between the users who have TeraGrid allocations and getting their work done on the TeraGrid. He coordinates the TeraGrid's ASTA program – Advanced Support for TeraGrid Applications.

Jim Marsteller, who heads our security efforts, leads the TeraGrid effort in security and oversees security policy and implementation. One of our other staffers, Laura McGinnis, has made significant contributions to the TeraGrid accounting system, which – as you can imagine – is quite an undertaking, to keep track of allocations at eight sites with many different systems.

Levine: Beyond this, I would add that with the TeraGrid there's, first, the computational science value to the research community in having a variety of resources and the facility to move between them. Secondly, there's the value of the individual components. In the first category, PSC's contribution is the things Ralph mentioned. In addition to that, at PSC we fulfill a unique function in providing two tightly coupled capability machines, LeMieux and the XT3, which between them over the last half-year or so have provided about 40 percent of overall TeraGrid usage.

HPCwire: What do you see as significant challenges in the years ahead for TeraGrid?
 
Levine: Many technical challenges are involved in creating value added to the resources if you take them as separate, individual pieces. With all the technical challenges, however, the biggest challenge is to not become overly absorbed in these many technical challenges for their own sake, but to keep our eyes on the prize – that is, to keep the focus clearly on making it easier for scientists to do science.

We also want to be able to expand the provider community both in size and in the nature of services provided, to include for example greater data-handling and archiving ability, and we need to continue the effort to broaden the community of users who can benefit from the TeraGrid, such as we're doing with Science Gateways, creating interfaces that provide easy entry to research communities within a field or discipline that share related scientific goals.

HPCwire: What's ahead for PSC?
 
Roskies: It's a very exciting time for computational science. We're pleased and lucky to be, in a sense, voyeurs – to be able to see wonderful and important scientific accomplishments made possible and happening because the technology is progressing at an astounding pace. To be a computational scientist is to live in very interesting times.

We're pleased that NSF is pushing ahead toward petascale computing, and we plan to contribute toward making this happen.

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Dr. Michael Levine is Professor of Physics at Carnegie Mellon University, specializing in theoretical particle physics. He is also a founder and Co-Scientific Director of the Pittsburgh Supercomputing Center (PSC). He is the author of numerous papers in computational, theoretical, and particle physics. His physics research over the last few years has been in high order quantum electrodynamics. His earlier work in Physics includes a series of papers applying symbolic computation methods and computational systems devised by him, to fundamental problems in electrodynamics done in collaboration with Professor Ralph Roskies. Professor Levine initiated Carnegie Mellon's degree program in Computational Physics and continues to teach courses in that program. In 1984, together with Ralph Roskies and James Kasdorf of Westinghouse Electric Company, he wrote the proposal to the National Science Foundation for what was eventually to become the PSC. As Scientific Director at PSC, he continues to oversee operations, plan its future course, and concern himself with its scientific impact. He also serves as the Associate Provost for Scientific Computing for Carnegie Mellon University.

Dr. Ralph Roskies is Professor of Physics at the University of Pittsburgh and a founder and Co-Scientific Director of the Pittsburgh Supercomputing Center (PSC). He is the author of over 60 papers in theoretical elementary particle physics. In 1984, together with Professor Michael Levine of Carnegie Mellon University and James Kasdorf from Westinghouse, he developed the proposal to the National Science Foundation for what became the PSC. As Scientific Director, Roskies oversees operations, plans its future course, and concerns himself with its scientific impact. The PSC has been a national leader in providing the highest capability computing to the US national research community. It has pioneered developments in file systems, heterogeneous computing, parallel algorithms and scientific visualization. It currently fields the Terascale Computing System and the first Cray XT3, two of the world's most powerful academically-based computing facilities dedicated to open scientific research. Roskies' pivotal role in developing and implementing the NSF allocation process has given him a very broad overview of leading computational science and close ties to its most prominent practitioners. He has served as advisor to and as reviewer of a large number of U.S. and international supercomputing centers.