Global HPCC Benchmarks in Chapel:STREAM Triad, Random Access, and FFT

HPC Challenge BOF, SC06Class 2 Submission

November 14, 2006

Brad Chamberlain, Steve Deitz,Mary Beth Hribar, Wayne Wong

Chapel Team, Cray Inc.

HPCC BOF, SC06

OverviewChapel: Cray’s HPCS language

Our approach to the HPC Challenge codes:• performance-minded• clear, intuitive, readable• general across…

typesproblem parametersmodular boundaries

HPCC BOF, SC06

Code Size Summary

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Chapel VersionProb. Size (common)Results and outputVerificationInitializationKernel declarationsKernel computation

STREAMTriad

RandomAccess FFT

HPCC BOF, SC06

Chapel Code Size Summary

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HPCC BOF, SC06

Chapel Code Size Summary1299

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HPCC BOF, SC06

STREAM Triad Overview

const ProblemSpace: domain(1) distributed(Block) = [1..m];var A, B, C: [ProblemSpace] elemType;

A = B + alpha * C;

HPCC BOF, SC06

STREAM Triad Overview

const ProblemSpace: domain(1) distributed(Block) = [1..m];var A, B, C: [ProblemSpace] elemType;

A = B + alpha * C;

ProblemSpace

Declare a 1D arithmetic domain (first-class index set)

L0 L1 L2 L3 L4

Specify its distribution

A

B

C

Use domain to declare distributed arrays

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Express computation using promoted scalar operators and whole-array references ⇒ parallel computation

HPCC BOF, SC06

Random Access Overview

[i in TableSpace] T(i) = i;

forall block in subBlocks(updateSpace) dofor r in RAStream(block.numIndices, block.low) doT(r & indexMask) ^= r;

HPCC BOF, SC06

Random Access Overview

[i in TableSpace] T(i) = i;

forall block in subBlocks(updateSpace) dofor r in RAStream(block.numIndices, block.low) doT(r & indexMask) ^= r;

Initialize table using a forall expression

Express table updates using forall- and for-loops

Random stream expressed modularly using an iterator

iterator RAStream(numvals, start:randType = 0): randType {

var val = getNthRandom(start);for i in 1..numvals {

getNextRandom(val);yield val;

}}

HPCC BOF, SC06

FFT Overview (radix 4)for i in [2..log2(numElements)) by 2 {

const m = span*radix, m2 = 2*m;

forall (k,k1) in (Adom by m2, 0..) {var wk2 = …, wk1 = …, wk3 = …;

forall j in [k..k+span) dobutterfly(wk1, wk2, wk3, A[j..j+3*span by span]);

wk1 = …; wk3 = …; wk2 *= 1.0i;

forall j in [k+m..k+m+span) dobutterfly(wk1, wk2, wk3, A[j..j+3*span by span]);

}span *= radix;

}

def butterfly(wk1, wk2, wk3, inout A:[1..radix]) { … }

HPCC BOF, SC06

FFT Overview (radix 4)for i in [2..log2(numElements)) by 2 {

const m = span*radix, m2 = 2*m;

forall (k,k1) in (Adom by m2, 0..) {var wk2 = …, wk1 = …, wk3 = …;

forall j in [k..k+span) dobutterfly(wk1, wk2, wk3, A[j..j+3*span by span]);

wk1 = …; wk3 = …; wk2 *= 1.0i;

forall j in [k+m..k+m+span) dobutterfly(wk1, wk2, wk3, A[j..j+3*span by span]);

}span *= radix;

}

def butterfly(wk1, wk2, wk3, inout A:[1..radix]) { … }

Parallelism expressed using nested forall-loops

Support for complex and imaginary math simplifies FFT arithmetic

Generic arguments allow routine to be called with complex, real, or imaginary twiddle factors

HPCC BOF, SC06

Chapel Compiler StatusAll codes compile and run with our current Chapel compiler• focus to date has been on…

prototyping Chapel, not performancetargeting a single locale

• platforms: Linux, Cygwin (Windows), Mac OS X, SunOS, …

No meaningful performance results yet• written report contains performance discussions for our codes

Upcoming milestones• December 2006: limited release to HPLS team• 2007: work on distributed-memory execution and optimizations• SC07: intend to have publishable performance results for HPCC`07

HPCC BOF, SC06

SummaryHave expressed HPCC codes attractively• clear, concise, general• express parallelism, compile and execute correctly on one locale• benefit from Chapel’s global-view parallelism• utilize generic programming and modern SW Engineering principles

Our written report contains:• complete source listings• detailed walkthroughs of our solutions as Chapel tutorial• performance notes for our implementations

Report and presentation available at our website:http://chapel.cs.washington.edu

We’re interested in your feedback:chapel_info@cray.com

Backup Slides

HPCC BOF, SC06

Compact High-Level Code…CGEP FT

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HPCC BOF, SC06

…need not perform poorlyCGEP FT

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See also Rice University’s recent D-HPF work…