Insertion Tree Phasers: Efficient and Scalable Barrier Synchronization for Fine-grained Parallelism

The last half year was an interesting departure from my actual PhD research. First, I though the idea of barriers and phasers might be interesting to incorporate into a virtual machine as part of my thesis, but as it turned out, they are much to high-level and are better off implemented in a library. The gain for direct support in a VM is just not proportional to the effort and restrictions which come with that step.

However, the time was not spend just for the sake of the academic exercise. I had a small idea how to improve the existing approaches and after quite some work, which proved that the initial idea was just broken, I had an algorithm that actually worked. Even so that idea is not contributing anything directly to my thesis, I was lucky enough to have a paper about it accepted at the IEEE HPCC’10 conference.

Abstract

This paper presents an algorithm and a data structure for scalable dynamic synchronization in fine-grained parallelism. The algorithm supports the full generality of phasers with dynamic, two-phase, and point-to-point synchronization. It retains the scalability of classical tree barriers, but provides unbounded dynamicity by employing a tailor-made insertion tree data structure.

It is the first completely documented implementation strategy for a scalable phaser synchronization construct. Our evaluation shows that it can be used as a drop-in replacement for classic barriers without harming performance, despite its additional complexity and potential for performance optimizations. Furthermore, our approach overcomes performance and scalability limitations which have been present in other phaser proposals.

  • Insertion Tree Phasers: Efficient and Scalable Barrier Synchronization for Fine-grained Parallelism, Stefan Marr, Stijn Verhaegen, Bruno De Fraine, Theo D’Hondt, Wolfgang De Meuter, Proceedings of the 12th IEEE International Conference on High Performance Computing and Communications (HPCC), IEEE CS, September (2010) (to appear).
  • Paper: PDF
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