<Insert Picture Here> OpenMP on Solaris

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2 <Insert Picture Here> OpenMP on Solaris Wenlong Zhang Senior Sales Consultant

3 Agenda What s OpenMP Why OpenMP OpenMP on Solaris <Insert Picture Here> 3

4 What s OpenMP Why OpenMP OpenMP on Solaris <Insert Picture Here> 4

5 What s OpenMP API for writing threaded programs in C, C++, and Fortran De-facto standard API for writing shared memory parallel applications in C, C++, and Fortran Consists of: Compiler directives Runtime routines Environment variables Specification: Maintained by the OpenMP Architecture Review Board Version 3.1 has been released 5

6 Memory Model private T T private Shared Memory T private T T private private Threads communicate via shared memory 6

7 Fork-Join Model of Execution Master thread only executing Start of parallel region Team of threads (includes master) executing End of parallel region (implied barrier) Master thread only executing 7

8 OpenMP Directives parallel for / do sections task barrier atomic critical (and more) 8

9 OpenMP Runtime Routines omp_set_num_threads() omp_set_dynamic() omp_set_nested() omp_get_thread_num() omp_in_parallel() omp_set_lock() omp_unset_lock() (and more) 9

10 OpenMP Environment Variables OMP_NUM_THREADS OMP_DYNAMIC OMP_NESTED OMP_WAIT_POLICY (and more) Additional Oracle-specific environment variables are supported: SUNW_MP_WARN SUNW_MP_PROCBIND SUNW_MP_WAIT_POLICY (and more) 10

11 What s OpenMP Why OpenMP OpenMP on Solaris <Insert Picture Here> 11

12 CPU Technology Evolution Comes to MultiCore/Multithread era Oracle Sparc M-Serial SPARC64 VII+ (M3): 4 cores x 2 threads M9000: up to 64 cpus Oracle T-series CPUs T4 cpu: 8 cores x 8 threads T4-4 Servers: 4 T4 cpus 12

13 OpenMP and Multicore/Multithread OpenMP is ideally suited for multicore/multithread architectures Memory and threading model map naturally Lightweight Mature Widely available and used 13

14 Advantages of OpenMP Good performance and scalability If you do it right... De-facto and mature standard An OpenMP program is portable Supported by a large number of compilers Requires little programming effort Allows the program to be parallelized incrementally 14

15 What s OpenMP Why OpenMP OpenMP on Solaris <Insert Picture Here> 15

16 Oracle Solaris Studio No.1 development platform for building scalable, secure and reliable mission-critical SPARC and x86 applications for the No.1 enterprise OS, Oracle Solaris Supports: Solaris on SPARC, Solaris/Linux on x86/x64 Processors supported: SPARC, Intel and AMD Fortran (f95), C (cc) and C++ (CC) compilers Math Libraries Performance Library Automatic Parallelization OpenMP MPI (aka Sun HPC Cluster Tools) 16

17 Oracle Solaris Studio Performance Analyzer Languages supported: Fortran, C, C++ and Java Parallel: AutoPar, OpenMP, POSIX/Solaris Threads Thread Analyzer Languages supported: Fortran, C, C++ Parallel: OpenMP, POSIX/Solaris Threads Solaris Studio IDE and other tools 17

18 Multicore Application Programming Pick your parallelisation strategy OpenMP Automatic parallelisation POSIX Threads Other... Profile your application Identify regions of code where time is spent Estimate performance gain from parallelisation Validate your code Data race and dead lock checking Memory access error detection Oracle Solaris Studio C/C++/Fortran Compilers Performance Analyzer Thread Analyzer & Discover 18

19 Parallel Programming Parallel programming is becoming more important with multi-threaded architectures Programming using POSIX threads is hard Two alternative approaches supported by Oracle Solaris Studio: OpenMP: User explicitly specifies what should be parallelized using compiler directives Automatic parallelization (autopar): Compiler automatically parallelizes loops in the program 19

20 OpenMP Support in Oracle Studio -xopenmp Equivalent to -xopenmp=parallel -xopenmp=parallel Enables recognition of OpenMP pragmas Requires at least optimization level -xo3 -xopenmp=noopt Enables recognition of OpenMP pragmas The program is parallelized accordingly, but no optimization is done -xopenmp=none Disables recognition of OpenMP pragmas (default) -xloopinfo Display parallelization messages on screen 20

21 OpenMP Example #include <omp.h>... #define N 100 int main (int argc, char *argv[]) {. /* Some initializations */ for (i=0; i < N; i++) a[i] = b[i] = i * 1.0; #pragma omp for for (i=0; i<n; i++) { c[i] = a[i] + b[i]; printf("thread %d: c[%d]= %f\n",tid,i,c[i]); } } } /* end of parallel section */ 21

22 OpenMP Example # cc -xo3 -xopenmp -xloopinfo -o demo demo.c "demo.c", line 13: not parallelized, unsafe dependence "demo.c", line 28: PARALLELIZED, user pragma used With Bash: #export OMP_NUM_THREADS=4 With Csh: #setevn OMP_NUM_THREADS 4 #timex./demo 22

23 Autoparallelisation Support Enable automatic parallellisation -xautopar Enable parallelisation of reductions -xreduction Parallelisation report -xloopinfo Set number of threads OMP_NUM_THREADS=N 23

24 Autoparallelisation Example #include <stdio.h> void init(int * array, int len) { for( int i=0; i<len; i++ ) { array[i] = i;} } int sum( int * array, int len) { int total = 0; for( int i=0; i<len; i++ ) {total += array[i];} return total; } 24

25 Autoparallelisation Example $ cc -O -xautopar -xloopinfo ex1.c "ex1.c", line 6: PARALLELIZED, and serial version generated "ex1.c", line 12: not parallelized, unsafe dependence (total) $ setenv OMP_NUM_THREADS 1; timex./a.out real 2.44 user 2.34 sys 0.06 $ setenv OMP_NUM_THREADS 2; timex./a.out real 1.78 << Elapsed time reduces user 2.33 << User time remains same sys

26 Tools Support Static Error checking under -xvpara Autoscoping Compiler commentary Runtime Error checking OpenMP Debugging using dbx Thread Analyzer Data race detection Deadlock detection OpenMP performance profiling 26

27 Thread Analyzer GUI 27

28 References OpenMP organization web site: OSS 12.3: OpenMP API User s Guide OSS 12.3: Debugging a Program With dbx OSS 12.3: Thread Analyzer User's Guide OSS 12.3: Performance Analyzer 28

29 <Insert Picture Here> OpenMP on Solaris Wenlong Zhang Senior Sales Consultant

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