@2012,Eko Didik Menjadwalkan For dan Lisensi …didik.blog.undip.ac.id/files/2012/02/TSK617-Kuliah7c-OpenMP...Pemrograman OpenMP (3) @2012,Eko Didik Widianto Menjadwalkan For dan Section

PemrogramanOpenMP (3)

@2012,Eko DidikWidianto

Menjadwalkan For danSection

OpenMP Tasks

Lisensi

Pemrograman OpenMP (3)Kuliah#9 TSK617 Pengolahan Paralel - TA 2011/2012

Eko Didik Widianto

Teknik Sistem Komputer - Universitas Diponegoro




OpenMP Tasks

Lisensi

Tentang Kuliah #9 Pemrograman OpenMP

I Akan dibahas tentang pemrograman paralel dengan OpenMPmenggunakan kompiler directive

I Arsitektur memori: shared (SMP, symmetricmulti-processor)

I Model programming: threadI Pokok Bahasan: (kuliah #8 akan membahas item yang

ditebalkan)

1. Pengantar OpenMP2. Membuat Thread3. Sinkronisasi dengan critical, atomic4. Loop dan Worksharing5. Sinkronisasi dengan barrier, single, master, ordered6. Environment Data7. Menjadwalkan for dan section8. Task di OpenMP 3.0




OpenMP Tasks

Lisensi

Kompetensi Dasar

I Setelah mempelajari bab ini, mahasiswa akan mampu:1. [C2] Mahasiswa memahami konsep pemrograman paralel

menggunakan OpenMP2. [C3] Mahasiswa akan mampu membuat program paralel

dari program serial menggunakan compiler-directive danpustaka-pustaka OpenMP

3. [C5] Mahasiswa akan mampu memprogram suatu aplikasikomputasi matrik menggunakan OpenMP serta menghitungfaktor speedupnya

I LinkI Website: http://didik.blog.undip.ac.id/2012/02/25/

kuliah-tsk-617-pengolahan-paralel-2011/I Email: [email protected]

http://didik.blog.undip.ac.id/2012/02/25/kuliah-tsk-617-pengolahan-paralel-2011/

http://didik.blog.undip.ac.id/2012/02/25/kuliah-tsk-617-pengolahan-paralel-2011/

mailto:[email protected]




OpenMP Tasks

Lisensi

Acknowledment

I Materi dan gambar didapat dari:I Tim Mattson, Larry Meadows (2008): “A Hands-on

Introduction to OpenMP“I Website: http://openmp.org/wp/resources/I OmpSCR: OpenMP Source Code Repository

(http://sourceforge.net/projects/ompscr/)

http://openmp.org/wp/resources/

http://sourceforge.net/projects/ompscr/




OpenMP Tasks

Lisensi

Bahasan

Menjadwalkan For dan SectionSections Worksharing ConstructSchedule Clause

OpenMP TasksOpenMP 3.0 and TasksOpenMP TasksTask ConstructTask ExampleTask and Thread SwitchingProfilingResources

Lisensi



Menjadwalkan For danSectionSections WorksharingConstruct

Schedule Clause

OpenMP Tasks

Lisensi

Bahasan



Lisensi




Schedule Clause

OpenMP Tasks

Lisensi

Sections Worksharing Construct

I The Sections worksharing construct gives a differentstructured block to each thread

#pragma omp parallel{#pragma omp sections{

#pragma omp sectionX_calculation();

#pragma omp sectionY_calculation();

#pragma omp sectionZ_calculation();

}

}

I By default, there is a barrier at the end of the “ompsections”. Use the “nowait” clause to turn off the barrier




Schedule Clause

OpenMP Tasks

Lisensi

Sections Example




Schedule Clause

OpenMP Tasks

Lisensi

Bahasan



Lisensi




Schedule Clause

OpenMP Tasks

Lisensi

Schedule Clause in Loop Worksharing for

I The schedule clause affects how loop iterations aremapped onto threads

I schedule(static [,chunk])Deal-out blocks of iterations of size “chunk” to each thread.

I schedule(dynamic[,chunk])Each thread grabs “chunk” iterations off a queue until alliterations have been handled.

I schedule(guided[,chunk])Threads dynamically grab blocks of iterations. The size ofthe block starts large and shrinks down to size “chunk” asthe calculation proceeds.

I schedule(runtime)Schedule and chunk size taken from the OMP_SCHEDULEenvironment variable (or the runtime library)

I for OpenMP 3.0




Schedule Clause

OpenMP Tasks

Lisensi

Static, Dynamic and Guided ScheduleClauses

ScheduleClause

When To Use Notes

STATIC Pre-determined andpredictable by the

programmer

Least work at runtime:scheduling done at

compile-time

DYNAMIC Unpredictable, highly variablework per iteration

Most work at runtime:complex scheduling logic

used at run-time

GUIDED Special case of dynamic toreduce scheduling overhead

Contoh: Linked List

I Program Serial: linked.cI Menampilkan urutan bilangan fibonacci:

F0 F0 F0 F0 F0 F0 F0 F0 F0 F0 F0 F0 F0 ...0 1 1 2 3 5 8 13 21 34 55 89 144 ...

Fn = Fn−1 + Fn−2 dengan nilai seed: F0 = 0, F1 = 1I menggunakan linked list

int fib(int n) {

int x, y;

if (n < 2) {

return (n);

} else {

x = fib(n - 1);

y = fib(n - 2);

return (x + y);

}

}Pascal Trianglea

aSumber: www.wikipedia.org

Linked List (cont)

I Buat program paralelnya (linked_omp25.c)I Ubah loop while menjadi for

I jumlah iterasi dihitung terlebih dahulu

p = init_list(p);head = p;

while (p != NULL) {processwork(p);p = p->next;

}

p = init_list(p);head = p;while (p != NULL) {p = p->next;count++;

}p = head;for(i=0; i<count; i++) {parr[i] = p;p = p->next;

}#pragma omp parallel{#pragma omp singleprintf(" %d threads \n",omp_get_num_threads());#pragma omp forfor(i=0; i<count; i++)processwork(parr[i]);

}

Latihan: Perkalian Matrik

I Program serial perkalian matriks: matmul.cI Buat program paralelnya

I Optimasi program dengan menjadwalkan loop




OpenMP TasksOpenMP 3.0 and Tasks

OpenMP Tasks

Task Construct

Task Example

Task and Thread Switching

Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

OpenMP Release History

I 2011: Release OpenMP 3.1 (http://www.openmp.org/mp-documents/OpenMP3.1.pdf)

http://www.openmp.org/mp-documents/OpenMP3.1.pdf

http://www.openmp.org/mp-documents/OpenMP3.1.pdf





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

OpenMP Tasks

I Tasking is added since OpenMP 3.0I A task has

I Code to executeI A data environment (it owns its data)I An assigned thread that executes the code and uses the

data

I Two activities: packaging and executionI Each encountering thread packages a new instance of a

task (code and data)I Some thread in the team executes the task





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Definitions

I Task constructI task directive plus structured block

I TaskI the package of code and instructions for allocating dataI created when a thread encounters a task construct

I Task regionI the dynamic sequence of instructions produced by the

execution of a task by a thread





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Tasks and OpenMP

I Tasks have been fully integrated into OpenMPI Key concept: OpenMP has always had tasks, we just

never called them that.I Thread encountering parallel construct packages up a set of

implicit tasks, one per threadI Team of threads is createdI Each thread in team is assigned to one of the tasks (and

tied to it)I Barrier holds original master thread until all implicit tasks

are finished

I We have simply added a way to create a task explicitlyfor the team to execute.





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Task Construct

#pragma omp task [clause[[,]clause] ...]

structured-block

I where clause can be one of:if (expression)

I When the if clause expression evaluates to false, an

undeferred task is generated, and the encountering

thread must suspend the current task region, for

which execution cannot be resumed until the generated

task is completed

untiedI If present, any thread in the team can resume the

task region after a suspension

shared (list)

private (list)

firstprivate (list)

default( shared | none )





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

When/where are tasks complete?

I At thread barriers, explicit or implicitI applies to all tasks generated in the current parallel region

up to the barrierI matches user expectation

I At task barriersI i.e. Wait until all tasks defined in the current task have

completed.

#pragma omp taskwait





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Task ExampleParallel Pointer Chasing using Tasks

#pragma omp parallel{#pragma omp single private(p){p = listhead ;

while (p) {#pragma omp task // p is �rstprivate inside this task

process (p)p=next (p) ;

}}

}





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Task ExampleParallel Pointer Chasing on Multiple Lists using Tasks

#pragma omp parallel{#pragma omp for private(p)for ( int i =0; i <numlists ; i++) {p = listheads [ i ] ;while (p ) {#pragma omp taskprocess (p)p=next (p ) ;}

}

}





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Task Switching

I When a thread encounters a task scheduling point, it isallowed to suspend the current task and execute another(called task switching)

I Generating task will have to suspend for a while

I It can then return to the original task and resume

#pragma omp single

{

for (i=0; i<ONEZILLION; i++)

#pragma omp task

process(item[i]);

}

I With task switching, the executing thread can:I execute an already generated task (draining the “task pool”)I dive into the encountered task (could be very

cache-friendly)





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Thread Switching

#pragma omp single

{

#pragma omp task untied

for (i=0; i<ONEZILLION; i++)

#pragma omp task

process(item[i]);

}

I Generating task is suspended and executing threadswitches to a long task

I With thread switching, the generating task can be resumedby a different thread





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Profiling

I Bagaimana melakukan profiling kode paralel?





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Inserting Profiling Code

I Use OpenMP function omp_get_wtime() to get timestamp

#include <omp.h>#de�ne ORDER 1000double start, end;....start = omp_get_wtime();<paralel code>end = omp_get_wtime();printf("Compute Time: %f seconds\n", end - start);dN = (double)ORDER;m�ops = 2.0 * dN * dN * dN/(1000000.0* run_time);printf(" Order %d multiplication at %f m�ops\n", OR-DER, m�ops);

...





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

Bahasan



Lisensi





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

OpenMP Resources

I OmpSCR: OpenMP Source Code Repository(http://sourceforge.net/projects/ompscr/)

http://sourceforge.net/projects/ompscr/





OpenMP Tasks

Task Construct

Task Example


Profiling

Resources

Lisensi

OpenMP On the Real World

I Christian Terboven, Dieter an Mey, “OpenMP in the RealWorld”




OpenMP Tasks

Lisensi

Lisensi

Creative Common Attribution-ShareAlike 3.0 Unported (CCBY-SA 3.0)

I Anda bebas:I untuk Membagikan — untuk menyalin, mendistribusikan,

dan menyebarkan karya, danI untuk Remix — untuk mengadaptasikan karya

I Di bawah persyaratan berikut:I Atribusi — Anda harus memberikan atribusi karya sesuai

dengan cara-cara yang diminta oleh pembuat karyatersebut atau pihak yang mengeluarkan lisensi.

I Pembagian Serupa — Jika Anda mengubah, menambah,atau membuat karya lain menggunakan karya ini, Andahanya boleh menyebarkan karya tersebut hanya denganlisensi yang sama, serupa, atau kompatibel.

I Lihat: Creative Commons Attribution-ShareAlike 3.0Unported License

http://creativecommons.org/licenses/by-sa/3.0/

http://creativecommons.org/licenses/by-sa/3.0/

Documents

@2012,Eko Didik Menjadwalkan For dan Lisensi …didik.blog.undip.ac.id/files/2012/02/TSK617-Kuliah7c-OpenMP...Pemrograman OpenMP (3) @2012,Eko Didik Widianto Menjadwalkan For dan Section