OMPi: A portable C compiler for OpenMP V2.0 Elias Leontiadis George Tzoumas Vassilios V....

OMPi:A portable C compiler for OpenMP V2.0

Elias LeontiadisGeorge TzoumasVassilios V. DimakopoulosUniversity of Ioannina

EWOMP 2003 2 OMPi - University of Ioannina

Presentation

Introduction

OMPi

OMPi Performance

Conclusions


The OpenMP specification

High level API for parallel programming in a shared memory environment

Fortran Version 1.0, October 1997 Version 1.1, November 1999 Version 2.0, November 2000

C/C++ Version 1.0, October 1998 Version 2.0, March 2002

New features such as timing routines copyprivate and num_threads clauses variable reprivatization static threadprivate


OpenMP compilers

Commercial compilers for specific machines SUN, SGI, Intel, Fujitsu, etc.

OpenMP compiler projects (usually portable) Nanos OdinMP/CCp Intone project Omni


Presentation

Introduction

OMPi

OMPi Performance

Conclusions


OMPi

Portable C compiler for OpenMP

Adheres to V.2.0

Produces ANSI C code with POSIX threads library calls

Written entirely in C


Compilation process

C sourcefile OMPi

generatedC file

system Ccompiler (cc)

objectfiles

objectfile

OMPilibrary

systemlinker

a.out


Code transformations

parallel construct code is moved into a (thread) function

a struct is declared containing pointers to non-global shared variables

private variables are redeclared locally in the function body

original code is replaced by code that creates a team of threads executing the function

master thread executes the function, too


Exampleint a; /* global */

int main()

{

int b, c;

#pragma omp parallel num_threads(3) \ private(c)

{

c = b + a;

. . .

}

}

int a;

typedef struct { /* shared vars structure */

int (*b); /* b is shared, non-global */

} par0_t;

int main()

{

int b, c;

_omp_initialize();

{

/* declare par0_vars, the shared var struct */

_OMP_PARALLEL_DECL_VARSTRUCT(par0);

/* par0_vars->b will point to real b */

_OMP_PARALLEL_INIT_VAR(par0, b);

/* Run the threads */

_omp_create_team(3, _OMP_THREAD, par0_thread,

(void *) &par0_vars);

_omp_destroy_team(_OMP_THREAD->parent);

}

}

void *par0_thread(void *_omp_thread_data)

{

int _dummy = _omp_assign_key(_omp_thread_data);

int (*b) = &_OMP_VARREF(par0, b);

int c;

c = (*(b)) + a;

. . .

}


Work sharing constructs

sections construct a switch-case block is created the code of each section is moved into a case of the switch

block any thread may execute any section

for construct each thread computes the bounds of the next chunk to execute then, if a chunk is available, executes the for-loop within the

computed bounds


Threads

a pool of threads is created when the program starts, all threads are sleeping

initial pool size is number of CPUs or $OMP_NUM_THREADS

user can request a specific number of threads by using the num_threads clause or omp_set_num_threads()


Presentation

Introduction

OMPi

OMPi Performance

Conclusions


Benchmarks

NAS parallel benchmarks OpenMP C version of ported by Omni group (v2.3) Results for Class W

Edinburgh University microbenchmarks (EPCC) Measure synchronization overheads


Platforms

SGI origin 2000 system 48 MIPS R10000 CPUs IRIX 6.5

Compaq proliant ML 570 2 Intel Xeon CPUs Redhat Linux 9.0

SUN E-1000 Server 4 Sparc CPUs Solaris 5.7


Compilers

OdinMP/CCp v1.02

Omni v1.4a

Intel C/C++ compiler (ICC) v7.1

Mipspro v7.3


Compilation times for 2-CPU Linux system

0

10

20

30

40

50

60

70

bt lu sp

seco

nd

s

odin

omni

ompi

icc

Compilation times for the SGI Origin 2000 system

0

20

40

60

80

100

120

140

160

180

200

bt lu sp

se

con

ds

odin

omni

ompi

mipspro

NAS parallel benchmarks Compilation Time


NAS parallel benchmarksSGI Origin 2000 (execution time)

10

20

30

40

50

60

70

80

90

100

110

1 2 3 4 5 6 7 8

seco

nd

s

number of threads

bt.W

ompi

omni

mipspro


NAS parallel benchmarksSGI Origin 2000

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8

seco

nd

s

number of threads

ompi

omni

mipspro

cg.W



1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

1 2 3 4 5 6 7 8

se

con

ds

number of threads

ft.W

ompi

omni

mipspro



20

40

60

80

100

120

140

160

1 2 3 4 5 6 7 8

se

con

ds

number of threads

lu.W

ompi

omnimipspro


NAS parallel benchmarks Sun E-1000

200

300

400

500

600

700

800

900

1000

1 2 3 4

se

con

ds

number of threads

bt.Wompiomni

10

20

30

40

50

60

70

80

90

1 2 3 4

se

con

ds

number of threads

cg.Wompiomni

10

15

20

25

30

35

40

1 2 3 4

se

con

ds

ft.Wompiomni

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4

se

con

ds

number of threads

lu.Wompiomni


EPCC microbenchmarksSGI (overheads)

0

100

200

300

400

500

600

700

800

900

1000

1 2 3 4 5 6 7 8

mic

rose

cond

s

number of threads

ompiparallel

for

parallel for

barrier

single

critical

lock unlock

ordered

atomic

reduction

0

100

200

300

400

500

600

700

800

900

1000

1 2 3 4 5 6 7 8

mic

rose

cond

s

number of threads

odinparallel

for

parallel for

barrier

single

critical

lock unlock

ordered

atomic

reduction


EPCC microbenchmarksSUN

0

200

400

600

800

1000

1200

1400

1 2 3 4

mic

rose

cond

s

number of threads

ompiparallel

forparallel for

barriersinglecritical

lock unlockorderedatomic

reduction

0

200

400

600

800

1000

1200

1400

1 2 3 4

mic

rose

cond

s

number of threads

omniparallel

forparallel for

barriersinglecritical

lock unlockorderedatomic

reduction


Presentation

Introduction

OMPi

OMPi Performance

Conclusions


Conclusions

C compiler for OpenMP V.2.0

Written in C, generated code uses pthreads

Tested on Linux, Solaris, Irix

Performance satisfactory, comparable with native compilers


Current status

Target solaris threads, sproc

Improve overheads (e.g. ordered)

Improve produced code (optimizations)

Profiling code

Thank you

http://www.cs.uoi.gr/~ompi

OMPi: A portable C compiler for OpenMP V2.0 Elias Leontiadis George Tzoumas Vassilios V....

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