1 / 21

Scaling to New Heights

Scaling to New Heights. Retrospective IEEE/ACM SC2002 Conference Baltimore, MD. Introduction. More than 80 researchers from universities, research centers, and corporations around the country attended the first "Scaling to New Heights" workshop, May 20 and 21, at PSC.

summer
Télécharger la présentation

Scaling to New Heights

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Scaling to New Heights Retrospective IEEE/ACM SC2002 Conference Baltimore, MD

  2. Introduction • More than 80 researchers from universities, research centers, and corporations around the country attended the first "Scaling to New Heights" workshop, May 20 and 21, at PSC. • Sponsored by the NSF leading-edge centers (NCSA, PSC, SDSC) together with the Center for Computational Sciences (ORNL) and NERSC, the workshop included a poster session, invited and contributed talks, and a panel. • Participants examined issues involved in adapting and developing research software to effectively exploit systems comprised of thousands of processors. The following slides represent a collection of ideas from the workshop

  3. Basic Concepts • All application components must scale • Control granularity; Virtualize • Incorporate latency tolerance • Reduce dependency on synchronization • Maintain per-process load; Facilitate balance Only new aspect is the degree to which these things matter

  4. Issues and Remedies • Granularity • Latencies • Synchronization • Load Balancing • Heterogeneous Considerations

  5. Granularity Define problem in terms of a large number of small objects independent of the process count • Object design considerations • Caching and other local effects • Communication-to-computation ratio • Control granularity through virtualization • Maintain per-process load level • Manage comms within virtual blocks, e.g. Converse • Facilitate dynamic load balancing

  6. Latencies • Network • Latency reduction lags improvement in flop rates; Much easier to grow bandwidth • Overlap communications and computations; Pipeline larger messages • Don’t wait – Speculate! • Software Overheads • Can be more significant than network delays • NUMA architectures Scalable designs must accommodate latencies

  7. Synchronization • Cost increases with the process count • Synchronization doesn’t scale well • Latencies come into play here too • Distributed resource exacerbates problems • Heterogeneity another significant obstacle • Regular communication patterns are often characterized by many synchronizations • Best suited to homogeneous co-located clusters Transition to asynchronous models?

  8. Load Balancing • Static load balancing • Reduces to granularity problem • Differences between processors and network segments are determined a priori • Dynamic process management requires distributed monitoring capabilities • Must be scalable • System maps objects to processes

  9. Heterogeneous Considerations • Similar but different processors or network components configured within a single cluster • Different clock rates, NICs, etc. • Distinct processors, networking segments, and operating systems operating at a distance • Grid resources Elevates significance of dynamic load balancing; Data-driven objects immediately adaptable

  10. Speedup Processors Poor Scalability?

  11. Speedup Processors Good Scalability?

  12. Speedup Processors Performance Comparison

  13. Tools • Automated algorithm selection and performance tuning by empirical means, e.g. ATLAS • Generate space of algorithms and search for fastest implementations by running them • Scalability prediction, e.g. PMaC Lab • Develop performance models (machine profiles; application signatures) and trending patterns Identify/fix bottlenecks; choose new methods?

  14. Case Study:NAMD Scalable Molecular Dynamics • Three-dimensional object-oriented code • Message-driven execution capability • Fixed problem sizes determined by biomolecular structures • Embedded PME electrostatics processor • Asynchronous communications

  15. Case Study:Summary • As more processes are used to solve the given fixed-size problems, benchmark times decrease to a few milliseconds • PME communication times and operating system loads are significant in this range • Scaling to many thousands of processes is almost certainly achievable now given a large enough problem • 700 atoms/process x 3,000 processes = 2.1M atoms

  16. Contacts and References • David O’Neal oneal@ncsa.uiuc.edu • John Urbanic urbanic@psc.edu • Sergiu Sanielevici sergiu@psc.edu Workshop materials: www.psc.edu/training/scaling/workshop.html

  17. Topics for Discussion • How should large, scalable computational science problems be posed? • Should existing algorithms and codes be modified or should new ones be developed? • Should agencies explicitly fund collaborations to develop industrial-strength, efficient, scalable codes? • What should cyber-infrastructure builders and operators do to help scientists develop and run good applications?

More Related