HPCwire recently spoke with Marie-Christine Sawley, director of the Swiss National Supercomputing Center (CSCS), about its use of the relatively new HPC Challenge benchmark for recent large-scale supercomputer procurement. The HPC Challenge, co-sponsored by the National Science Foundation, U.S. Department of Energy and DARPA HPCS (High Productivity Computing Systems) program, was introduced at the SC2003 conference. Assembled by Jack Dongarra and Piotr Luszczek of the University of Tennessee, with collaborators from the U.S. and Europe, the benchmark suite includes Linpack and tests of other capabilities that can make a major difference in the real-world performance of HPC systems. Although HPCwire expects the U.S. government to begin using the HPC Challenge in procurements soon, CSCS may be the world's first major site to do this.

HPCwire: Tell me about CSCS.

Sawley: We are the Swiss National Supercomputing Center, located in Lugano, south of Zurich. We serve scientific researchers throughout Switzerland and beyond. CSCS was created in 1991 to provide leadership-class computing for high- end science nationwide and to support breakthrough science, academic partnerships and world-class connectivity. We are an autonomous unit of ETH- Zurich.

HPCwire: Why does your organization need a large-scale supercomputer?

Sawley: Since 2004, we've operated on a mandate to enrich our portfolio with some of the most demanding users and scientific applications. We had few of these applications at CSCS before, but we knew there were more out there. Users in this category were either trying to outsource their work on systems they could access, or they were limiting their work. We wanted to give them a way to scale up. We decided to extend our computing infrastructure with a tightly coupled, leadership-class system.

HPCwire: What were the goals for your "Horizon" procurement?

Sawley: We wanted a capability machine based on MPP architecture, with 1,000 or more CPUs and a fast interconnect. We ended up choosing a Cray XT3. Any Swiss researcher will be able to apply for computing time on this machine. The targeted applications domains are computational chemistry, materials science, molecular dynamics, physics and climate science. For the future, there could also be some interest in financial applications based on stochastic modeling.

HPCwire: How did you become aware of the HPC Challenge benchmark suite?

Sawley: We recognized the limitations of Linpack and witnessed the development of the HPC Challenge, especially through our partnership in SOS with Sandia and Oak Ridge.

HPCwire: Why did you decide to use HPC Challenge?

Sawley: Because we can measure and analyze the characteristic dimensions of a given supercomputer architecture with it. It allows you to base your investment not only on the sustained Gigaflop/s or wall clock time of a few applications, but to develop a procurement strategy which is part of an overall supercomputer portfolio management strategy. You also don't have to hand as many user codes over to the manufacturers for benchmarking and optimization during a call for tender project. When you have them run the HPC Challenge suite, they are running a suite of synthetic benchmarks that are well known in the community. This lowers the burden on the bidders, speeds your procurement project, and still allows you to estimate the effects of a given architecture on your key user applications by mapping their characteristic requirements onto the various HPCC benchmark test results.

HPCwire: How did the HPC Challenge fit into your other procurement criteria?

Sawley: The major challenge we faced was characterizing how applications would map onto architectures. Running HPC Challenge plus user codes turned out to be complementary. We assigned the heaviest weighting to the HPC Challenge results. Performance on user codes also played a role, of course, and we had to complete the procurement benchmark suite with another synthetic benchmark for file system I/O.

HPCwire: What was your experience using the HPC Challenge?

Sawley: Neither the bidders nor we had any major problems. It created a level playing field for the bidders and there was no resistance from them about using it, even though this was the first time they had to deal with the HPC Challenge in a procurement, at least in Europe. Most of the bidders approached it as a challenge, in the most positive sense. There were no surprises created by the HPC Challenge suite.

HPCwire: Since your pioneering use of the HPC Challenge, have you heard from other HPC sites that are interested in using it too?

Sawley: We have heard from a number of sites in the U.S. and a couple in Europe.

HPCwire: Would you use HPC Challenge again? Would you recommend it to others?

Sawley: We would definitely recommend it to others, and would certainly use it again for this kind of procurement, in which you are preparing for a major step forward. Our biggest machine before this procurement was 250 processors. If you want to take a big step forward, as we did, HPC Challenge is particularly well designed for high-level testing of your workload. There's always a certain amount of risk, of course. We had internal discussions on how to benchmark with codes that were in development, and using HPC Challenge seem to offer a sensible way to characterize the systems.

HPCwire: Do you think you'll succeed in attracting more demanding applications and users?

Sawley: Yes, because there's an unmet demand we will be able to address with our new Red Storm-based supercomputer. Some momentum has already started. Before this procurement, our largest applications used 128 CPUs; but as word got around that this bigger system was coming, ideas for scaling up really began flourishing. It has already spurred innovation.

HPCwire: What are your biggest challenges as an organization? How do you plan to overcome them?

Sawley: One challenge when you're growing is not to lose focus. We are mitigating this risk by adding scientific services for our users, including benchmarking, performance modeling, advanced visualization and other tools for data evaluation. So, we're enhancing our competencies. We need to deliver all this, of course. We have a performance agreement with our funding bodies, with key performance indicators we have to meet.

HPCwire: What is CSCS' position on industrial relations and technology transfer?

Sawley: Our belief is that simply selling cycles to industry is hard and you often don't learn much if the collaboration stops there. The most successful model, in our view and in our experience, is to construct projects with specific goals. Both parties learn in this model. With utility computing, you don't get that learning: the users take the added knowledge away with them. Technology transfer is complex.

At CSCS, our approach is to make sure we have a scientific leader, someone who acts as a principal investigator and can validate the science. Beyond that, innovation requires an ecosystem, an environment that fosters the open exchange of information and knowledge transfer. For our "Horizon" procurement and the progress that will come from it, Switzerland's Paul Scherrer Institut was the right partner, because they came to us with deep scientific knowledge and an unmet need. To run their HPC applications, they had to go outside Switzerland before. Their applications were growing and they believed in CSCS. We didn't have many applications that needed this level of scaling one year ago, but the situation is changing rapidly.

HPCwire: What's on the horizon for CSCS?

Sawley: We are the national center in a relatively small country, so we need to develop stronger awareness of CSCS and our scientific services. We expect from our large-scale system and services to make CSCS a more attractive partner for international collaborations. In a number of scientific fields, this country has outstanding researchers. You can't innovate without excellent researchers. I think the HPC Challenge is also a good fit when you want to innovate. You wouldn't use it in every situation and for every procurement, but it works well when you need to make a big leap forward. Having access to a leadership class scientific instrument such as an innovative high performance computer is a strong stimulus for new thinking.