Understanding CPU Dispatching in the Intel® IPP Libraries

Introduction

Intel® Integrated Performance Primitives (Intel® IPP) is a cross-architecture software library that provides a broad range of library functions for image processing, signal processing, data compression, and computer vision, as well as math support routines for such processing capabilities. Intel IPP is optimized for the wide range of Intel microprocessors.

One of the key advantages within Intel IPP is performance. The performance advantage comes through per processor architecture optimized functions, compiled into one single library. Intel IPP functions are “dispatched” at run-time. The “dispatcher” chooses which of these processor-specific optimized libraries to use when the application makes a call into the Intel IPP library. This is done to maximize each function’s use of the underlying vector instructions and other architecture-specific features.

This paper covers CPU dispatching of the Intel IPP library in more detail. After reading this article you will understand how CPU dispatching works and which libraries are needed for which processor architecture. Further documentation on Intel IPP can be found at Intel® Integrated Performance Primitives – Documentation.

Dispatcher

Dispatching refers to the process of detecting CPU features at run-time and then selecting the Intel IPP optimized library set that corresponds to your CPU. For example, in the <ipp directory>\bin directory, the ippiy8.dll library file contains the 64-bit optimized image processing libraries for processors with Intel® SSE4.2; ‘ippi’ refers to the image processing library, ‘y8’ refers to 64-bit SSE4.2 architecture.

Note: You can build custom processor-specific libraries that do not require the dispatcher, but that is outside thescope of this article. Please read this IPP linkage models article for information on how to build custom versions of the Intel IPP library.

In the general case, the “dispatcher” identifies the run-time processor only once, at library initialization time. It sets an internal table or variable that directs your calls to the internal functions that match your architecture. For example, ippsCopy_8u(), may have multiple implementations stored in the library, with each version optimized to a specific Intel® processor architecture. Thus, the y8_ippsCopy_8u() version of ippsCopy_8u() is called by dispatcher when running on an Intel processor with Intel® SSE4.2, because it is optimized for this processor architecture.

Note: Intel IPP architectures generally correspond to SIMD existing in supported procesors (SSE4.2, AVX2, AVX512).

Initializing the Intel® IPP Dispatcher

The process of identifying the specific processor being used, and initialization of the dispatcher, should be performed before making any calls into the Intel IPP library. If you are using a dynamic link library this process is handled automatically when the dynamic link library is initialized. However, if you are using a static library you must perform this step manually. See this article on the ipp*Init*() functions for more information on how to do this.

The following table lists all the architecture codes defined by the Intel IPP library through version 11.3 of the product. Note that some of these Intel IPP architectures have been deprecated and are no longer supported in the current version of the product.