Customer application can be parallelized by using the following techniques:
You do not create threads in your application but specify the parallel mode within the FFT module of Intel MKL. See Intel MKL User's Guide for more information on how to do this. See also Example "Using Intel MKL Internal Threading Mode".
You create threads in the application yourself and have each thread perform all stages of FFT implementation, including descriptor initialization, FFT computation, and descriptor deallocation. In this case, each descriptor is used only within its corresponding thread. It is recommended to set single-threaded mode for Intel MKL. See Example "Using Parallel Mode with Multiple Descriptors Initialized in a Parallel Region".
You create threads in the application yourself after initializing all FFT descriptors. This implies that threading is employed for parallel FFT computation only, and the descriptors are released upon return from the parallel region. In this case, each descriptor is used only within its corresponding thread. It is obligatory to explicitly set the single-threaded mode for Intel MKL, otherwise, the actual number of threads may differ from one, because the DftiCommitDescriptor function is not in a parallel region. See Example "Using Parallel Mode with Multiple Descriptors Initialized in One Thread".
- You create threads in the application yourself after initializing the only FFT descriptor. This implies that threading is employed for parallel FFT computation only, and the descriptor is released upon return from the parallel region. In this case, each thread uses the same descriptor. See Example "Using Parallel Mode with a Common Descriptor".
In cases "a", "b", and "c", listed above, set the parameter DFTI_NUMBER_OF_USER_THREADS to 1 (its default value), since each particular descriptor instance is used only in a single thread.
In case "d", use the DftiSetValue() function to set the DFTI_NUMBER_OF_USER_THREADS to the actual number of FFT computation threads, because multiple threads will be using the same descriptor. If this setting is not done, your program will work incorrectly or fail, since the descriptor contains individual data for each thread.
Warning
Avoid parallelizing your program and employing the Intel MKL internal threading simultaneously because this will slow down the performance. Note that in case "d" above, FFT computation is automatically initiated in a single-threading mode.
Do not change the number of threads after the DftiCommitDescriptor() function completed FFT initialization.
Optimization Notice |
|---|
|
Intel compilers, associated libraries and associated development tools may include or utilize options that optimize for instruction sets that are available in both Intel and non-Intel microprocessors (for example SIMD instruction sets), but do not optimize equally for non-Intel microprocessors. In addition, certain compiler options for Intel compilers, including some that are not specific to Intel micro-architecture, are reserved for Intel microprocessors. For a detailed description of Intel compiler options, including the instruction sets and specific microprocessors they implicate, please refer to the "Intel Compiler User and Reference Guides" under "Compiler Options." Many library routines that are part of Intel compiler products are more highly optimized for Intel microprocessors than for other microprocessors. While the compilers and libraries in Intel compiler products offer optimizations for both Intel and Intel-compatible microprocessors, depending on the options you select, your code and other factors, you likely will get extra performance on Intel microprocessors. Intel compilers, associated libraries and associated development tools may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include Intel® Streaming SIMD Extensions 2 (Intel® SSE2), Intel® Streaming SIMD Extensions 3 (Intel® SSE3), and Supplemental Streaming SIMD Extensions 3 (Intel SSSE3) instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. While Intel believes our compilers and libraries are excellent choices to assist in obtaining the best performance on Intel and non-Intel microprocessors, Intel recommends that you evaluate other compilers and libraries to determine which best meet your requirements. We hope to win your business by striving to offer the best performance of any compiler or library; please let us know if you find we do not. Notice revision #20110307 |