Departement Informatik, Universität Basel
Departement Informatik, Universität Basel
Departement Informatik, Universität Basel
Departement Informatik, Universität Basel

Colloquium - 10.10.2017

TitleIsoefficiency in Practice: Configuring and Understanding the Performance of Task-based Applications
SpeakerFelix Wolf, Professor of Computer Science, Department of Computer Science, TU Darmstadt, Germany
TimeTuesday, October 10, 2017 from 12:15 – 13:15
LocationDepartment of Mathematics and Computer Science, Seminar Room 05.002, University of Basel, Spiegelgasse 5, Basel

Abstract
Task-based programming offers an elegant way to express units of computation and the dependencies among them, making it easier to distribute the computational load evenly across multiple cores. However, this separation of problem decomposition and parallelism requires a sufficiently large input problem to achieve satisfactory efficiency on a given number of cores. Unfortunately, finding a good match between input size and core count usually requires significant experimentation, which is expensive and sometimes even impractical. In this talk, we propose an
automated empirical method for finding the isoefficiency function of a task-based program, binding efficiency, core count, and the input size in one analytical expression. This allows the latter two to be adjusted according to given (realistic) efficiency objectives. Moreover, we not only find (i) the actual isoefficiency function but also (ii) the function one would yield if the program execution was free of resource contention and (iii) an upper bound that could only be reached if the program was able to maintain its average parallelism throughout its execution. The difference between the three helps to explain low efficiency, and in particular, it helps to differentiate between resource contention and structural conflicts related to task dependencies or scheduling. The insights gained can be used to co-design programs and shared system resources.

Speaker Biographical Sketch
Felix Wolf is a full professor at the Department of Computer Science of TU Darmstadt, where he is head of the Laboratory for Parallel Programming. He is interested in methods, tools, and algorithms that support the development and deployment of parallel software systems in various stages of their life cycle. Since the beginning of his professional career, Prof. Wolf has been designing programming tools for HPC. He has made major contributions to Scalasca, a widely used open-source tool for the performance analysis of HPC applications.
Moreover, he has initiated and serves as spokesman of the Virtual Institute – High Productivity Supercomputing, an international initiative of academic HPC programming-tool builders aimed at the
enhancement, integration, and deployment of their products. Felix Wolf has published more than a hundred refereed articles on parallel computing, several of which have received awards.

After the talk an informal apéro will be offered. I hope you’ll be joining us.