Omp For Mac

2020年11月26日
Download: http://gg.gg/n8221
Optimize applications on multicore architectures
*Clang-omp For Mac
*Omp Forecasting
*Omp Machine Learning
*Omp For Schedule Dynamic
*Omp For Macbook Pro
*Omp For MacroWhy use OpenMP
When compiling with a brewed version of clang-omp, since brewed gcc for mac will fail on the objective-c files included (should this be an issue too, with someone?), and normal mac clang does not support openMP, the cmake file shipped wi. #pragma omp target teams distribute parallel for simd: Complete. Clang does not support any constructs/updates from upcoming OpenMP 5.0 except for reduction-based clauses in the task and target-based directives. AArch64, and PPC64 on Linux, Windows, and mac OS. Ows, and mac OS.
Parallelizing C/C++ code improves runtime speed and efficiency by distributing independent execution tasks to as many CPU cores as possible. The improvements in speed and efficiency are proportional to the number of CPU cores available.
OpenMP allows a programmer to gain the benefits of parallel code without doing all the work required to setup a parallel environment. These benefits include thread creation, work distribution, resource management, and more. With OpenMP code readability is almost as good as a single threaded application but simultaneously performs at the rate of a parallelized application.How OpenMP works
OpenMP allows you to describe certain sections of the code as ’parallel’. A parallel section is run by every thread in the OpenMP thread space. The non-parallel sections are run by the same thread that started the program. This is also known as the Master thread. The number of threads in the thread space is specified either in code by the developer or by the environment during program startup. Figure 1 illustrates how this works for a parallelization factor of 4 threads.Figure 1. How OpenMP works
Creating a parallel section is simple, it involves creating an ’omp parallel’ block. All executable code within this block is run by every thread in the thread team. Listing 1 shows an application that prints ’Hello World’ using an ’omp parallel’ blockListing 1. Basic HelloWorld
Listing 2 is the output of Listing 1 with 4 parallel threads.Listing 2. HelloWorld outputOpenMP constructs on z/OS C/C++
There are many aspects to OpenMP. OpenMP takes care of:
*The creation of threads and distribution of tasks to threads
*Creation of a thread-private stack that stores thread-private variables and
*The synchronization of concurrent threads to prevent race conditions and other well known challenges that arise from parallel programming practices.
The sections below explain how to utilize these aspects of OpenMP.Create threads and distribute work
Use the construct in Listing 3 to create parallel sections that are run by each thread in the thread team.Listing 3. Parallel directive
Parallel threads don’t have to execute the same block of code. You can divide the code into ’sections’ that can run by any one thread. These sections are run in parallel. Threads do not proceed beyond the ’sections’ block until each thread has finished running within that ’sections’ block, as shown in Listing 4.Listing 4. Section directive
If a parallel section only contains sections, you can combine the parallel and sections construct to improve code readability, as shown in Listing 5.Listing 5. Combined parallel section directive
Sometimes you may want to start a certain block of code by only one thread in a parallel section. For example, you might want to print the status of a global variable once. To do this, use ’single’ instead of ’section’. There is no thread synchronization as with the ’sections’ block. Therefore, the single block doesn’t hold up any other threads running parallel to it. Listing 6 provides an example of this.Listing 6. Single directive
The master thread, and only the master thread, can be forced to run a block of code using the master construct shown in Listing 7. This is just like the single block but forces the master thread to execute the block.Listing 7. Master directive
You can parallelize a ’for’ loop using the for construct. The means that the iterations of the loop are distributed equally among all thread members in the team as shown in Listing 8.Listing 8. Fordirective
If your parallel section only contains a parallel ’for’ loop, you can combine the two constructs as shown in Listing 9.Listing 9. Combined “parallel for” directive
Remember that the loop iterations are not run in order of iteration number. This means iteration 9 (run by its own thread) can run before iteration 6 (which is also run in its own thread). However, there might be sections of code that you want to run in sequential order just as in a non-parallel loop. You can do this by wrapping that block of code in an ordered block. You also need to specify the ordered clause for the enclosing parallel ’for’ directive.Listing 10. Ordered block inside a “for” block using an “ordered” clauseThread private variables
You may want to declare a variable outside of a parallel section but treat it as a thread private variable inside of a parallel section. This means that every thread in the parallel region has its own version of that variable. To do this, use the private clause as shown in Listing 11.Listing 11. Private clause
In Listing 11, the thread specific variables are initialized like any other int variables. If you want to initialize these variables with the value of the global variable, use the firstprivate clause shown in Listing 12.Listing 12. Firstprivate clause
If you want to update the global variable with the private variable from the last thread that finished the parallel section,use the lastprivate clause.Listing 13. Lastprivate clause
You can declare a global variable to be thread-private in all parallel regions and maintain its value across all parallel regions. This concept is similar to a thread-private static global variable. To do this, use the threadprivate directive.
Note: There is a distinction between a private variable (thread and parallel region specific) and a thread-private variable (thread specific).Listing 14. Threadprivate directive
Before a parallel section starts to run, you might want to copy the value of a thread-private variable in the master thread to all other threads. This is achieved with copyin. An example of copyin is shown in Listing 15.Listing 15. Copyin clause
When multiple threads read and write to shared variables, you might want make sure that all threads have ’flushed’ their updates to the original memory location, and re-read them into their registers. This ensures all threads have the same view of these shared variables and is shown in Listing 16.Listing 16. Flush directive
Use the reduction clause to combine the values of private variables after a parallel section is complete and store that in the global variable in the master thread. . Specify the name of the variable and the operator used to combine the values. Listing 17 is an example of uses the ’reduction’ clause which adds the private variables and stores them in the master thread variable. Note that the ’reduction’ clause implicitly gives each thread its own copy of the variable with a default initial value.Listing 17. Reduction clauseSynchronization
As a parallel programmer, you need to account for critical sections. These are sections of the code that should be run by one thread at a time. This is usually required when data shared by parallel threads is being modified. You can use the critical directive to create a critical section, as shown in Listing 18.Listing 18. Critical directive
Create a barrier if you need all parallel threads to reach a certain point before any one of them can proceed further.. This means that no thread will go past a barrier until all other threads have reached the barrier, as shown in Listing 19.
Note: There is an implicit barrier at the end of every parallel section. The master thread cannot proceed until all threads have finished parallel section execution.Listing 19. Barrier directiveCompiling for OpenMP
You have now written code that uses OpenMP parallelism. When you compile this code using your regular compile options, you will not see parallel execution. In fact, it runs it as though it were single threaded. To produce an executable that utilizes OpenMP parallelism, here are some options to consider at compile time:
*-qSMP=EXPLICIT enables symmetric multi-processing and OpenMP parallel execution. A side effect is that -O2 and -qHOT are enabled automatically. You can also just use -qSMP since EXPLICIT is a default sub-option.
*-q64 is required because symmetric multi-processing only works in 64-bit mode. This means OpenMP only works in 64-bit mode.
*-O2 and -qHOT are side effects of -qSMP. However, you can minimize optimization within parallel code sections by specifying -qSMP=NOOPT. This makes debugging parallel sections easier. In the default case, if nothing is specified, it is -qSMP=OPT.Limitations
The following limitations regarding OpenMP on XLC v2.1 for z/OS are:
*Debugger support is not available for programs compiled with -qSMP=EXPLICIT.
*Nested parallelism is not supported. This means you should not use a ’omp parallel’ block inside another ’omp parallel’ block.Summary
The examples in this article illustrate the power and usability of the OpenMP API to create parallel programs on z/OS.Downloadable resourcesRelated topics
*Download a free trial version of Rational software.
*For more information about Open MP:
*Visit the OpenMP website
*Read the OpenMP 3.1 standard specification, pdf
*Follow the steps in the in-depth tutorial of the OpenMP 3.1 standard
*Read the Introduction to parallel computingDevelopment activity of OpenMP support in clang/llvm compiler has moved to www.llvm.org. Please get OpenMP-enabled clang (OpenMP 3.1 is fully supported in clang/llvm 3.7) and contribute to its further development there. This web-site is maintained for archival purposes only.
The OpenMP (Open Multi-Processing) specification is a standard for a set of compiler directives, library routines, and environment variables that can be used to specify shared memory parallelism in Fortran and C/C++ programs.
This project implements OpenMP support in the Clang C language family front-end for the LLVM compiler. The current scope of the project is to support the OpenMP 4.0 specification.
November 27, 2015 - Further development of OpenMP support in clang/llvm compiler moved to www.llvm.org. This site is maintained for archival purposes only. Thank you to everyone who contributed all these years! September 9, 2014 - Upgrade to clang/LLVM 3.5, updated link to LLVM OpenMP library. June 10, 2014 - Initial support of omp teams distribute [simd],omp target teams distribute [simd],omp teams distribute parallel for [simd]and omp target teams distribute parallel for [simd] directives (just parsing and semantic analysis). June 9, 2014 - Initial support of omp target data,omp target updateand omp target teams directives (just parsing and semantic analysis). May 6, 2014 - Initial support of omp target, teams, distribute, distribute simd, distribute for, distribute parallel for, distribute parallel for simd and omp declare targetdirectives (no actual offloading, just parsing and semantic analysis). April 11, 2014 - Added support of omp cancel and omp cancellation pointdirectives. March 14, 2014 - Added support of depend clause in omp taskdirective, support for omp parallel for simd directive. February 6, 2014 - Upgrade to clang/llvm 3.4. December 6, 2013 - Added support of variable length arrays in OpenMP constructs. November 25, 2013 - Added support of omp simd, omp declare reduction directives. September 27, 2013 - Added support of proc_bind clause. August 23, 2013 - Initial release.Getting the source code
The source code structure follows Clang/LLVM: http://llvm.org/docs/GettingStarted.html. To run (rather than just compile) code you need to get and build an Intel® OpenMP* Runtime Library.
Also you can try to use trunk-based version of the compiler (supported by Hal Finkel)Building
To build clang with OpenMP support just follow the clang/LLVM compiler’s standard build procedure (see Getting Started: Building and Running Clang).Using
To use the newly installed compiler, add the following to your environment. On Mac OS X, replace LD_LIBRARY_PATH with DYLD_LIBRARY_PATH.Clang-omp For Mac
When you build a program that uses OpenMP directives, add the following options to enable OpenMP support and link to the runtime library.Using clang-omp with Xcode Instructions are provided by Sebastian Stenzel.
*Install clang-omp using homebrew: brew install llvm.
*Add llvm binaries to your path using : echo ’export PATH=’/usr/local/opt/llvm/bin:$PATH’ >> ~/.bash_profile.
*Create a new Xcode project.
*Under Build Settings
*Add a new user-defined setting CC with the value /usr/local/bin/clang-omp
*Add -fopenmp to Other C Flags
*Add /usr/local/include to Header Search Paths
*SetEnable Modules (C and Objective-C)toNo.
*Under Build Phases
*Add /usr/local/lib/libiomp5.dylib to Link Binary With Libraries Done. You can now #include <libiomp/omp.h> and start using Omp Forecasting#pragma omp ... in your source code. A simple example
Confirm that the compiler is working correctly by saving the above code to a file.
Compilation should proceed with no errors or warnings.
Execute the output ./hello. You should see more than one “Hello” line with different thread numbers. Note that the lines may be mixed together. If you see only one, try setting the environment variable OMP_NUM_THREADS to some number (say 4) and try again.
If you would like to see performance impact, you can try to compile and execute a more complex example Matrices Multiplication.
We welcome contributions of all kinds: patches, code reviews, testing and bug reports.
However, as any other open source project, we have to maintain some level of control to prevent complete chaos and keep a single architectural direction. You can send your patches here for review and commit; also, we are very open with granting commit access rights to recognized members of Clang/LLVM community. Omp Machine Learning
We plan eventually to contribute this OpenMP implementation to the Clang trunk, where it will be governed by existing Clang/LLVM community development policies.
Full support for OpenMP 3.1 and most of OpenMP 4.0 features (except for offloading) are implemented. This implementation relies on the Intel OpenMP API, and should be used along with Intel® OpenMP* Runtime Library that supports that API (available from www.openmprtl.org).
The following openly available OpenMP test suites pass:
*OpenMP Validation Suite by OpenUH Research Compiler - passed 119 tests of 123.Supported platforms
OS: Linux or Mac OS X Architecture: x86, x86-64, PowerPC, ArmImportant Note
Please note that this is a preliminary version. While everything is carefully tested and works fine, there are known internal design quality issues. We plan to refactor some parts of the code before submitting them to Clang trunk. And yes, any help with this would be appreciated!
Among known design issues are: Omp For Schedule Dynamic
*Combined constructs (#pragma omp parallel for and #pragma omp parallel sections). Currently these constructs are represented as a pair of #pragma omp parallel and #pragma omp for/sections constructs. This solution leads to ugly representation in AST because of the troubles with the variables capturing.
*Calculation of iteration indices for #pragma omp for is not quite optimal. AST representation of this construct also is not very good and should be re-designed.
*Analysis of atomic constructs and loops should be reworked for better diagnostics and readability. Also, please note that this development is based on latest released clang (3.5), not what is currently under development in clang trunk. External projects based on OpenMP implementation hosted here. If you want your project to be listed, please let us know.
*Experimental ’check’ clause for ’parallel for’ pragma by Luis Felipe Mattos and Juan Salamanca from UNICAMP (Brazil).Omp For Macbook Pro
LLVM, Clang, and Compiler-rt are distributed under LLVM’s the University of Illinois/NCSA Open Source License. In addition to the ’UIUC’ BSD-Style license license, the runtime library component of LLVM (Compiler_rt) is also licensed under the MIT License. For details, including information about third-party components, see LICENSE.txt in the code repositories.Omp For Macro
If you would like to report a bug, or make a feature request, you can submit an issue in Github here.
Download: http://gg.gg/n8221

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