Declarative Programming Languages for Multicore Architecures

1. Declarative Programming Languagesfor Multicore Architecures Workshop 15 January 2006

2. Welcome… • …to the first workshop on Declarative Programming Languages for Multicore Architectures! • Multicores are coming • We need to program them • Correctly! • Implicit parallelism is promising • But can it be made effective Declarative Programming Languages for Multicore Architectures

3. Logistics • Workshop, breakfast, and breaks here in Cypress • Lunch in suite J2 – buffet style • Informal style • Ask questions • Discuss • Mixture of retrospective, work in progress, and speculation on the future • Name tags at the back if you don’t have one • No wireless  Declarative Programming Languages for Multicore Architectures

4. Programme Declarative Programming Languages for Multicore Architectures

5. Panel:Lessons from the Past andWhat it Means for Multicores • Questions to ponder: • What worked and what did not work in the research of the 80s and 90s? • What are the remaining hard problems from previous research? • Which hard problems are relevant to multicores, and which are mitigated? • What does the experience of 80s and 90s suggest for multicore design/architecture? Declarative Programming Languages for Multicore Architectures

6. Thanks • To all of you for attending • To all the presenters • To Anwar Ghuloum, Leaf Petersen, and Jesse Fang for helping me to organise the workshop • To Intel’s PSL for sponsoring the workshop • To Margarida Strickland for administrative support Declarative Programming Languages for Multicore Architectures

7. Keynote • The Evolution of Computing Architectures • Douglas Carmean • Senior Principal Architect • Intel Corporation Declarative Programming Languages for Multicore Architectures

8. Panel:Lessons from the Past andWhat it Means for Multicores • What worked and what did not work in the research of the 80s and 90s? • What are the remaining hard problems from previous research? • Which hard problems are relevant to multicores, and which are mitigated? • What does the experience of 80s and 90s suggest for multicore design/architecture? Declarative Programming Languages for Multicore Architectures

9. Summary • Hardware • Implicit parallelism • Language design • Key problems • Cross fertilisation • Hardware ideas • Intel • Next steps Declarative Programming Languages for Multicore Architectures

10. Hardware Summary • Three types of parallelism: • Vector units – floating point, but integer too • SMT – multiple register sets in single core • SMP – multiple cores on chip Declarative Programming Languages for Multicore Architectures

11. Implicit Parallelism Summary • Over promised, under delivered • Easy to generate lots of parallelism • Problem is to schedule • Cactus stacks, thunks worked well • Sequential (deterministic) semantics is important • Easier to debug Cost models are important Communication was a problem • Not with multicores Declarative Programming Languages for Multicore Architectures

12. Language Design Thoughts • Don’t commit to specific hardware • Don’t base the language on the implementation • Exact reduction operations are important (see Nesl) Domain specific languages • Bad idea, use libraries instead • Atomic great for when you have effects Declarative Programming Languages for Multicore Architectures

13. More Language Design Thoughts • Control of effects is very beneficial • Fewer writes • TM logs • Three layers of language: • Explicit – transactional memory, atomicity • Implicit – declarative and sequential • Data parallelism – especially vector Declarative Programming Languages for Multicore Architectures

14. Controversy • Are annotations needed? • No • Minimal (and vs or parallelism) • Strategies • Manuel’s ideas • Message Passing – good or bad? • MPI bad • Perhaps a good programming abstraction exists for certain applications Cost models Declarative Programming Languages for Multicore Architectures

15. Key Problems • Memory management • Concurrent GC is an important problem • Data locality • How to place data • Shared vs non-shared memory • Memory Models Cost Models Debugging Put the models together Thread packages and good low-level libraries Declarative Programming Languages for Multicore Architectures

16. Cross Fertilisation • Or-parallelism for search • What is the equivalent in FP? Nesl good at Vector, SMT, and SMP • Can LP do this too? • What are the similarities between the communities and can they exchange results? Declarative Programming Languages for Multicore Architectures

17. Hardware Ideas - General • General purpose mechanisms, language specific bad • Memory bandwidth is fundamental issue • Latency solved? • Dataflow? • Programmable hardware? Declarative Programming Languages for Multicore Architectures

18. Hardware Ideas - Specific • Hardware support for Transactional Memory • Read and/or write barriers for GC, TM, I-structs • Fast context switching, lightweight spawn & sched • No glass-jaws in synchronisation instructions • Non-shared memory • NUMA caches • Allocate in cache Declarative Programming Languages for Multicore Architectures

19. Intel • Feel free to talk to us: • Anwar, David, Leaf, Neal, and Rob PSL is working on: • McRT – threading, scheduling, and synchronisation • Pillar – target language (a la C--) for parallel languages Intel Research: • Jekyll, Autolocker, Lockbend, … Declarative Programming Languages for Multicore Architectures

20. This Workshop Follow On • Feel free to give me feedback at: • neal.glew@intel.com • A website will be constructed if presenters are willing to give me their slides • I’ll send a message when ready Declarative Programming Languages for Multicore Architectures

21. The Future • A once off? • Repeat again next year and then see? • Open? • Associated with what? Or by itself? • Something else? • Follow on for the hardware ideas? Declarative Programming Languages for Multicore Architectures