Frédéric Gava

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Frédéric Gava

Parallel I/O

Bulk-Synchronous Parallel MLIn

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Outline Introduction

• The BSP model

• The BSML language

External Memory in BSML

• Cost model

• Problems and solutions

Conclusion and Future Work

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Introduction

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Bulk Synchronous Parallelism +

Functional Programming = BSML

Advantages of the BSP model:1. Portability2. 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 environment3. Programs Proofs

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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:

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The BSP model

T(s) = (max0i<p wi) + hg + L

0 1 2 3 p-1Proc.

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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

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if vec at n then … else …

=

if

at n then e1 else e2

n

Global Conditional

… true bp-1…b1b0

e1

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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)

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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

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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

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Example Scan_list :

scan_list (+) <[0;1], [2;3], [4] >

Read/write values in blocks using tempory files

< [0;0+1], [0+1+2;0+1+2+3], [0+1+2+3+4] >

Benchmark

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Conclusion BSML = BSP + ML

External Memory in BSML

New cost model

New Primitives

Confluence

Compositional cost model

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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

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