HPC Consortium: Technical University of Denmark

Bernd Dammann, Associate Professor at the Technical University of Denmark spoke yesterday afternoon at the Sun HPC Consortium meeting here in Dresden. His talk focused on the benefits of Sun's Studio compiler and tools suite for education and HPC.

Sun Studio is an important tool for teaching students about HPC programming techniques at DTU, including data flow through cache-based systems, loop-based optimization techniques, pipelining, and general application tuning techniques. The particular programming course that Bernd described focuses on helping students understand how real computers work, how memory and CPUs are glued together -- the details they don't learn in more theoretical courses. However, once the students are exposed to these techniques they are surprised to learn that many of these techniques are applied automatically to their codes by modern compilers. Good news for ease of use, but frustrating for engineering students who typically don't like black boxes and prefer to understand internal details in such cases. Sun Studio solves this problem with its compiler commentary feature.

Compiler commentary allows the programmer to view their source code annotated with compiler-generated comments that describe in detail not just which optimizations were applied to the code, but also cases in which optimizations where not applied. Bernd showed several examples that illustrated how the feature works, including the use of the er_src utility to display source code with interleaved commentary.

The benefit, of course, of the compiler commentary is that a suitably educated programmer can use the information to find additional opportunities for performance improvement by making suitable changes to the code or by activating additional compiler features. For example, one of Bernd's examples showed the use of the -xrestrict compiler flag, which was not familiar to me. It allows the programmer to tell the compiler that pointers in the code are known not to overlap, which can potentially allow the compiler to significantly increase performance with additional optimizations. Cool.

Bernd noted that Sun's compiler commentary is "in the right place," namely in the binaries rather than in separate log files or merely displayed on a screen. By storing the commentary internally, it can be extracted and looked at later-- potentially long after compilation, which can be very useful.

Bernd then gave a brief overview of Sun's primary performance analysis tool, Sun Studio Performance Analyzer. He noted that it can display compiler commentary as well as a variety of application performance metrics (cpu usage, timelines, etc.) He praised it as a tool that both he and his students find very intuitive and easy to use.

Sun Studio is also used in a parallel programming course where it makes teaching OpenMP much easier. Being able to look at performance timelines for each thread to see OpenMP overheads and using the Thread Analyzer tool to detect data races were two examples. He also liked Sun's extension to OpenMP that allows the compiler to perform automatic scoping, which can be very useful in dealing with large, legacy codes with hundreds of variables.

Students at DTU have been using the Sun Studio tools for four years and like it a lot. They wished they could use the tools on Linux. Well, now they can.

Bernd ended his talk with some favorable comparisons of Sun Studio C against GCC and Intel C and showed an example of how easy it was to use the Sun tools to easily parallelize and debug a large, legacy Fortran code and get good parallel performance very quickly. He conclused with the observation that Sun Studio is a world-class product that is easy to learn and use. Bernd is now on my official list of favorite customers. :-)


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