OpenMP Paolo Burgio paolo.burgio@unimore.it A history of OpenMP - - PowerPoint PPT Presentation

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OpenMP Paolo Burgio paolo.burgio@unimore.it A history of OpenMP - - PowerPoint PPT Presentation

Dec 25, 2022 382 likes •521 views

An introduction to OpenMP Paolo Burgio paolo.burgio@unimore.it A history of OpenMP 1997 OpenMP for Fortran 1.0 1998 OpenMP for C/C++ 1.0 2000 Regular, loop-based parallelism OpenMP for Fortran 2.0 2002

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SLIDE 1

An introduction to OpenMP

Paolo Burgio paolo.burgio@unimore.it

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SLIDE 2

A history of OpenMP

› 1997

– OpenMP for Fortran 1.0

› 1998

– OpenMP for C/C++ 1.0

› 2000

– OpenMP for Fortran 2.0

› 2002

– OpenMP for C/C++ 2.5

› 2008

– OpenMP 3.0

› 2011

– OpenMP 3.1

› 2014

– OpenMP 4.5

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Regular, loop-based parallelism Irregular, parallelism ➔ tasking Heterogeneous parallelism, à la GP-GPU

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SLIDE 3

What is OpenMP?

› Let's start from definition

– https://en.wikipedia.org/wiki/OpenMP

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OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C, C++, and Fortran, on most platforms, processor architectures and operating systems, including Solaris, AIX, HP-UX, Linux, OS X, and Windows. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior

eng.wikipedia.org

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Application Programming Interface

› Eases programmers' life › Can be specific for specific domain

– Web, Databases…for parallel programming

› Examples

– POSIX Threads – CUDA – OpenCL – …

PARALLEL PROGRAMMING LT – 2017/18 4

OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C, C++, and Fortran, on most platforms, processor architectures and operating systems, including Solaris, AIX, HP-UX, Linux, OS X, and Windows. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior

eng.wikipedia.org

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SLIDE 5

A mix of …

› Many ways to do the same things

– Linux-like philosohpy – What's the difference?

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OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C, C++, and Fortran, on most platforms, processor architectures and operating systems, including Solaris, AIX, HP-UX, Linux, OS X, and Windows. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior

eng.wikipedia.org

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Why OpenMP?

› What makes it better e.g., than PThreads?

– Pragma-based interface – Transparent threading and memory management – We will this soon…

› What's missing?

– Poor control on threads (no scheduling) – "Team of threads" – Automatic memory management

› What's left?

– Programmer is in charge of synchronization – Programmer is in charge of memory consistency – As opposite to..caches

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"it's elegant and appealing"

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Cross-platform, cross-language

› OpenMP is a full technological stack › With a set of tools

– Compiler, runtime, OS support

› That ensures portability!!

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OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C, C++, and Fortran, on most platforms, processor architectures and operating systems, including Solaris, AIX, HP-UX, Linux, OS X, and Windows. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior

eng.wikipedia.org

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SLIDE 8

Find the difference

› Between…

– A standard – An implementation

› A standard usually gives guidelines on

– Behavior – (Common) Interface – De facto vs de iure

› A implementation is

– Platform(s)-specific – Lanugage(s)-specific – Has specific performance/Quality-of-Service QoS

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Shared memory

› As opposite to "physically" partitioned memory › Traditional "sequential" programming style

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OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C, C++, and Fortran, on most platforms, processor architectures and operating systems, including Solaris, AIX, HP-UX, Linux, OS X, and Windows. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior

eng.wikipedia.org

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Shared memory

› Coherence problem

– Memory consistency issue – Data races

› Can share data ptrs

– Ease-to-use

› Several paradigm ("flavours")

– Symmetric Multiprocessing – Distributed Shared memory – Partitioned Global Access Space

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Process P0 Shared memory

T T T

(read, write) (read, write)

DATUM

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Multi-processing

› What is multi-processing?

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OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C, C++, and Fortran, on most platforms, processor architectures and operating systems, including Solaris, AIX, HP-UX, Linux, OS X, and Windows. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior

eng.wikipedia.org

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Outline

› Expressing parallelism

– Understanding parallel threads

› Memory Data management

– Data clauses

› Synchronization

– Barriers, locks, critical sections

› Work partitioning

– Loops, sections, single work, tasks…

› Execution devices

– Target

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References

› "Calcolo parallelo" website

– http://hipert.unimore.it/people/paolob/pub/PhD/index.html

› My contacts

– paolo.burgio@unimore.it – http://hipert.mat.unimore.it/people/paolob/

› Useful links

– http://www.openmp.org

› A "small blog"

– http://www.google.com

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