forked from OSchip/llvm-project
2df65f87c1
It is reported that after enabling hidden helper thread, the program can hit the assertion `new_gtid < __kmp_threads_capacity` sometimes. The root cause is explained as follows. Let's say the default `__kmp_threads_capacity` is `N`. If hidden helper thread is enabled, `__kmp_threads_capacity` will be offset to `N+8` by default. If the number of threads we need exceeds `N+8`, e.g. via `num_threads` clause, we need to expand `__kmp_threads`. In `__kmp_expand_threads`, the expansion starts from `__kmp_threads_capacity`, and repeatedly doubling it until the new capacity meets the requirement. Let's assume the new requirement is `Y`. If `Y` happens to meet the constraint `(N+8)*2^X=Y` where `X` is the number of iterations, the new capacity is not enough because we have 8 slots for hidden helper threads. Here is an example. ``` #include <vector> int main(int argc, char *argv[]) { constexpr const size_t N = 1344; std::vector<int> data(N); #pragma omp parallel for for (unsigned i = 0; i < N; ++i) { data[i] = i; } #pragma omp parallel for num_threads(N) for (unsigned i = 0; i < N; ++i) { data[i] += i; } return 0; } ``` My CPU is 20C40T, then `__kmp_threads_capacity` is 160. After offset, `__kmp_threads_capacity` becomes 168. `1344 = (160+8)*2^3`, then the assertions hit. Reviewed By: protze.joachim Differential Revision: https://reviews.llvm.org/D98838 |
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README.txt |
README.txt
README for the LLVM* OpenMP* Runtime Library ============================================ How to Build Documentation ========================== The main documentation is in Doxygen* format, and this distribution should come with pre-built PDF documentation in doc/Reference.pdf. However, an HTML version can be built by executing: % doxygen doc/doxygen/config in the runtime directory. That will produce HTML documentation in the doc/doxygen/generated directory, which can be accessed by pointing a web browser at the index.html file there. If you don't have Doxygen installed, you can download it from www.doxygen.org. How to Build the LLVM* OpenMP* Runtime Library ============================================== In-tree build: $ cd where-you-want-to-live Check out openmp into llvm/projects $ cd where-you-want-to-build $ mkdir build && cd build $ cmake path/to/llvm -DCMAKE_C_COMPILER=<C compiler> -DCMAKE_CXX_COMPILER=<C++ compiler> $ make omp Out-of-tree build: $ cd where-you-want-to-live Check out openmp $ cd where-you-want-to-live/openmp/runtime $ mkdir build && cd build $ cmake path/to/openmp -DCMAKE_C_COMPILER=<C compiler> -DCMAKE_CXX_COMPILER=<C++ compiler> $ make For details about building, please look at README.rst in the parent directory. Architectures Supported ======================= * IA-32 architecture * Intel(R) 64 architecture * Intel(R) Many Integrated Core Architecture * ARM* architecture * Aarch64 (64-bit ARM) architecture * IBM(R) Power architecture (big endian) * IBM(R) Power architecture (little endian) * MIPS and MIPS64 architecture * RISCV64 architecture Supported RTL Build Configurations ================================== Supported Architectures: IA-32 architecture, Intel(R) 64, and Intel(R) Many Integrated Core Architecture ---------------------------------------------- | icc/icl | gcc | clang | --------------|---------------|----------------------------| | Linux* OS | Yes(1,5) | Yes(2,4) | Yes(4,6,7) | | FreeBSD* | No | No | Yes(4,6,7,8) | | OS X* | Yes(1,3,4) | No | Yes(4,6,7) | | Windows* OS | Yes(1,4) | No | No | ------------------------------------------------------------ (1) On IA-32 architecture and Intel(R) 64, icc/icl versions 12.x are supported (12.1 is recommended). (2) GCC* version 4.7 is supported. (3) For icc on OS X*, OS X* version 10.5.8 is supported. (4) Intel(R) Many Integrated Core Architecture not supported. (5) On Intel(R) Many Integrated Core Architecture, icc/icl versions 13.0 or later are required. (6) Clang* version 3.3 is supported. (7) Clang* currently does not offer a software-implemented 128 bit extended precision type. Thus, all entry points reliant on this type are removed from the library and cannot be called in the user program. The following functions are not available: __kmpc_atomic_cmplx16_* __kmpc_atomic_float16_* __kmpc_atomic_*_fp (8) Community contribution provided AS IS, not tested by Intel. Supported Architectures: IBM(R) Power 7 and Power 8 ----------------------------- | gcc | clang | --------------|------------|--------------| | Linux* OS | Yes(1,2) | Yes(3,4) | ------------------------------------------- (1) On Power 7, gcc version 4.8.2 is supported. (2) On Power 8, gcc version 4.8.2 is supported. (3) On Power 7, clang version 3.7 is supported. (4) On Power 8, clang version 3.7 is supported. Front-end Compilers that work with this RTL =========================================== The following compilers are known to do compatible code generation for this RTL: clang (from the OpenMP development branch at http://clang-omp.github.io/ ), Intel compilers, GCC. See the documentation for more details. ----------------------------------------------------------------------- Notices ======= *Other names and brands may be claimed as the property of others.