PAPP 2004 Gava1 Frédéric Gava Parallel I/O Bulk-Synchronous Parallel ML In

PAPP 2004 Gava2 Outline  Introduction The BSP model The BSML language  External Memory in BSML Cost model Problems and solutions  Conclusion and Future Work

PAPP 2004 Gava3 Introduction

PAPP 2004 Gava4 Bulk Synchronous Parallelism + Functional Programming = BSML Advantages of the BSP model: 1.Portability 2.Scalability, deadlock free 3.Simple cost model  Performance prediction Advantages of functional programming: 1.High level features (higher order functions, pattern-matching, concrete types, etc…) 2.Savety of the environment 3.Programs Proofs

PAPP 2004 Gava The Caraml Project  Funds by the ACI Grid program (French National Grid program) First phase: safety Second phase: multiprogramming Third phase: extensions for Grid computing  Tools and applications  Organized in 3 phases:

6 The BSP model T(s) = (max 0  i<p w i ) + h  g + L p-1 Proc.

PAPP 2004 Gava7 The BSML language  Library for the « Objective Caml » language (called BSMLlib)  Operations on a parallel data structure called vector:  par  Operations to access to the BSP parameters :  4 Operations on a parallel vectors

8 if vec at n then … else … = if at n then e1 else e2 n Global Conditional  …trueb p-1 …b1b1 b0b0 e1

PAPP 2004 Gava9 External Memory

Model We have: M = Size of the main memory D = Number of disks B = Size of one block in a disk G = Time to read/write in parallel B blocks (D*B data)

PAPP 2004 Gava11 Problem let bug = mkpar (fun pid -> if pid=0 then open_write « toto.dat » else NOTHING) in open_read « toto.dat » « local side effects » => modification of the global environment

12 Solutions  Two file systems local files => one files system on each process global files : o a shared files system o or replicate local files on a different directory)  New primitives for the differents files  Confluence of the semantics  Compositional cost model

PAPP 2004 Gava13 Example Scan_list : scan_list (+) Read/write values in blocks using tempory files

Benchmark

PAPP 2004 Gava15 Conclusion  BSML = BSP + ML  External Memory in BSML  New cost model  New Primitives  Confluence  Compositional cost model

16 Future Work  Add to BSML :  Parallel composition  Exceptions  Pattern – matching of parallel values  Polymorphic type system for BSML with I/O  Implementation of « big » applications

PAPP 2004 Gava17