Sly and the RoarVM: Exploring the Manycore Future of Programming

Sly and the RoarVM Exploring the Manycore Future of Programming Renaissance Project h=p://so@.vub.ac.be/~smarr/renaissance/ Stefan Marr So@ware Languages Lab, Vrije Universiteit Brussel ExaScience Lab, 2011-‐08-‐24

Agenda •  Context: Renaissance Project •  Sly –  Demo –  Language Overview •  RoarVM –  Intercore Messaging –  Read-‐mostly heap –  Pauseless GC •  Outlook 23/08/11 2

Renaissance Project •  CollaboraWon between –  IBM Research, Portland State Univ, VUB •  Problem –  Parallel systems are nondeterminisWc –  CommunicaWon is expensive •  The vision –  Embrace nondeterminism –  Harness emergence –  Conﬁdence → Delay 23/08/11 3

Demo 24/08/11 4

Possible Real Life ApplicaWon Image: h=p://blogs.technet.com/b/andrew/ archive/2007/08/22/olap-‐cubes-‐and-‐ mulWdimensional-‐analysis.aspx 23/08/11 5

Possible Real Life ApplicaWon •  ACK: ongoing work at IBM Research •  Online analyWcal processing (OLAP) –  Business intelligence, reporWng, data mining •  Query mulWdimensional data sets –  Includes dependent/calculated data dimensions –  Sync. required to avoid use of stale data •  Without sync.: how to bound error? –  RecalculaWng, refreshing results 23/08/11 6

Sly •  Ensembles: collecWons represenWng a whole, mulW-‐part enWWes –  e.g. a ﬂock of birds •  Adverbs: modiﬁers to operands –  individualLY, serialLY, randomLY: n •  Gerunds: reducWon semanWcs –  averagING, selectINGpredicate, ensemblING 23/08/11 7

Examples of Boids •  Every boid is its own thread, no synch. computeCentroid ^ self flock boids averagINGserialLYposition computeNeighbors ^ self flock boids selectINGisNear: self matchVelocityWithNeighbors ^ self neighbors averagINGvelocity / 8.0 More details: h=p://so@.vub.ac.be/~smarr/renaissance/sly3-‐overview/ 23/08/11 8

Virtual Machines for Manycore Architectures ROARVM 23/08/11 9

The Manycore Problem (from [2]) •  Shared memory 10 words access very expensive 1 word 0 250 500 750 1000 –  Inter-‐core messaging DMA Load Mem. –  Purpose-‐speciﬁc networks Msg: 3 hops Msg: 1 hop 23/08/11 10

Architecture Overview •  Core = Interpreter Instance = OS Process/Thread •  ‘Single System Image’/shared memory VM 23/08/11 11

Message-‐Passing between Interpreters •  To avoid main-‐memory latency •  VM internal use only –  GC •  preGCAcWon + ACK •  doAllRootsHere + Response, … –  SafepoinWng •  requestSafepointOnOtherCores •  grantSafepoint, … 23/08/11 12

Memory System •  Object table, moving stop-‐the-‐world GC –  Usually allocaWon on heap of local core Object Heap 24/08/11 13

Memory System •  Object table, moving stop-‐the-‐world GC –  Usually allocaWon on heap of local core Global Safepoint Object Heap 23/08/11 14

Read-‐Mostly Heap [2] •  TILE64 cache coherency VERY expensive –  Read-‐mostly heap: incoherent, ‘user managed CC’ Cache Cache Cache Read/Write Read-‐mostly 23/08/11 15

Stop-‐the-‐World in Manycore Era? Work Run out of space Arrival at safe point Do garbage collect Work 23/08/11 16

Stop-‐the-‐World in Manycore Era? … … … … 23/08/11 17

Pauseless GC •  Based on a paper by Click et al., 2005 [3] •  No global synchronizaWon –  Local checkpoints: 1 mutator and GC thread •  ConWnuously running GC threads •  Load-‐Value-‐barrier + self-‐healing of stale refs. •  Constant performance overhead –  Without hardware support •  Easy to implement (2 MA students, 1 month) 23/08/11 18

OUTLOOK 23/08/11 19

Conclusion •  Sly: map/reduce-‐like programming model –  Based on ensembles, adverbs and gerunds •  RoarVM –  Research arWfact, stable, used daily –  No opWmizaWon of sequenWal performance –  Tested up to 59cores –  Shows weak scalability 23/08/11 20

Outlook •  Sly –  Ideas for non-‐linear syntax –  Algorithms for nondeterminisWc programming •  RoarVM: focus on research –  VMs are mulW-‐language plarorms –  Support for concurrency models –  DSLs for speciﬁc concurrent/parallel problems –  Language guarantees in inter-‐model interacWon 23/08/11 21

References and Material [1] J. Pallas and D. Ungar. MulWprocessor Smalltalk: A Case Study of a MulWprocessor-‐based Programming Environment. In PLDI ’88, p. 268–277. ACM, 1988. [2] D. Ungar and S. Adams. HosWng an Object Heap on Manycore Hardware: An ExploraWon. In DLS’09, p. 99-‐110. ACM, 2009. [3] C. Click, G. Tene, and M. Wolf. The Pauseless GC Algorithm. In VEE ’05, p. 46-‐56. ACM, 2005. [4] D. Ungar, D. Kimelman, and S. Adams. Inconsistency Robustness for Scalability in InteracWve Concurrent‑Update In-‐Memory MOLAP Cubes. In Inconsistency Robustness Symposium 2011. [5] P. Inostroza Valdera. The Sly3 Programming Language: An IntroducWon and Analysis. h=p://so@.vub.ac.be/~smarr/renaissance/sly3-‐overview/ [6] Renaissance Project: h=p://so@.vub.ac.be/~smarr/renaissance/ 23/08/11 Roundup and Conclusion 22

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Sly and the RoarVM: Exploring the Manycore Future of Programming

by Stefan Marr on Aug 24, 2011

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