SetCpuFeatures
SetCpuFeatures
Sets the processor-specific library code for the specified processor features.
Syntax
IppStatus ippSetCpuFeatures(Ipp64u
cpuFeatures
);
Include Files
ippcore.h
Parameters
- cpuFeatures
- Features to be supported by the library. Refer toippdefs.hforippCPUID_xxdefinition.
Description
This function sets the processor-specific code of the Intel IPP library according to the processor features specified in
cpuFeatures
. You can use the following predefined sets of features (the
FM
suffix below means
feature mask
):
32-bit code:
#define PX_FM ( ippCPUID_MMX | ippCPUID_SSE ) #define W7_FM ( PX_FM | ippCPUID_SSE2 ) #define V8_FM ( W7_FM | ippCPUID_SSE3 | ippCPUID_SSSE3 ) #define S8_FM ( V8_FM | ippCPUID_MOVBE ) #define P8_FM ( V8_FM | ippCPUID_SSE41 | ippCPUID_SSE42 | ippCPUID_AES | ippCPUID_CLMUL | ippCPUID_SHA ) #define G9_FM ( P8_FM | ippCPUID_AVX | ippAVX_ENABLEDBYOS | ippCPUID_RDRAND | ippCPUID_F16C ) #define H9_FM ( G9_FM | ippCPUID_MOVBE | ippCPUID_AVX2 | ippCPUID_ADCOX | ippCPUID_RDSEED | ippCPUID_PREFETCHW )
64-bit code:
#define PX_FM ( ippCPUID_MMX | ippCPUID_SSE | ippCPUID_SSE2 ) #define M7_FM ( PX_FM | ippCPUID_SSE3 ) #define U8_FM ( M7_FM | ippCPUID_SSSE3 ) #define N8_FM ( U8_FM | ippCPUID_MOVBE ) #define Y8_FM ( U8_FM | ippCPUID_SSE41 | ippCPUID_SSE42 | ippCPUID_AES | ippCPUID_CLMUL | ippCPUID_SHA ) #define E9_FM ( Y8_FM | ippCPUID_AVX | ippAVX_ENABLEDBYOS | ippCPUID_RDRAND | ippCPUID_F16C ) #define L9_FM ( E9_FM | ippCPUID_MOVBE | ippCPUID_AVX2 | ippCPUID_ADCOX | ippCPUID_RDSEED | ippCPUID_PREFETCHW ) #define K0_FM ( L9_FM | ippCPUID_AVX512F )
Do not use any other Intel IPP function while
ippSetCpuFeatures
is executing. Otherwise, your application behavior is undefined.
To avoid initialization of internal structures for one Intel® architecture and then call of the processing function that is optimized for another architecture, do not use the
ippSetCpuFeatures
function in chains of Intel IPP connected calls like
<processing function
GetSize
+
<processing function
Init
+
<processing function>
. Otherwise, Intel IPP functionality behavior is undefined.
Intel IPP library supports two internal sets of CPU features:
- Real CPU features: the features that are supported by the CPU at which the library is executed. These features are read-only and can be obtained with theippGetCpuFeaturesfunction.
- and set withEnabled features: the features that are enabled externally to Intel IPP by the application. These features are read-write and can be obtained with ippGetEnabledCpuFeaturesippSetCpuFeatures.
The
ippSetCpuFeatures
function provides additional flexibility in measuring performance improvements reached by using specific CPU features. For example, the call of the
ippInit()
(or the first call of any Intel IPP function for the library version starting with 9.0) function in an application running on the 4th Generation Intel® Core™ i7 processor with 64-bit OS installed dispatches the L9 code version optimized for Intel® Advanced Vector Extensions 2 (Intel® AVX2) with several other features like fast 16-bit floating point support, Intel® AES New Instructions (Intel® AES-NI), PCLMULQDQ new instructions support.
To check performance improvement for all Intel IPP functionality reached by using Intel® AVX2, you can run a benchmark for the currently dispatched version of code and then compare performance with the Intel® Advanced Vector Extensions (Intel® AVX) version of code with Intel® AVX2 disabled. To disable Intel AVX2, call
ippSetCpuFeatures(E9_FM)
. To enable Intel AVX2 back, call
ippSetCpuFeatures( L9_FM )
. Thus, you can use the
ippSetCpuFeatures
function to dispatch any version of Intel IPP code and enable/disable specific CPU features. If you are not well familiar with the features of your CPU, use the
ippInit()
function (or auto-initialization mechanism available starting with Intel IPP 9.0) for the default library behavior.
Optimization Notice
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Intel's compilers 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 SSE2, SSE3, and 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. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.
Notice revision #20110804
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Return Values
- ippStsNoErr
- Indicates that the required processor-specific code is successfully set.
- ippStsCpuMismatch
- Indicates that the specified processor features are not valid. Previously set code is used. If the requested feature is below the minimal supported by thepxlibrary - that is Intel® Streaming SIMD Extensions (Intel® SSE) for IA-32 and Intel® SSE2 for Intel® 64 architecture,pxcode is dispatched.
- ippStsFeatureNotSupported
- Indicates that the current CPU does not support at least one of the requested features. If theippCPUID_NOCHECKbit of thecpuFeaturesparameter is set to 1, these not supported features are enabled, otherwise - disabled.
- ippStsUnknownFeature
- Indicates that at least one of the requested features is unknown. It means that the feature is not defined in theippdefs.hfile. Further behavior of the library depends on known features passed tocpuFeatures. Unknown features are ignored.
- ippStsFeaturesCombination
- Indicates that the combination of features is not correct. For example,ippCPUID_AVX2bit is set to 1 incpuFeatures, but at least one of theippCPUID_MMX,ippCPUID_SSE, …,ippCPUID_AVXbits is not set. All these missing bits, if supported by CPU, are set to 1. This means that if the library supports the Intel® AVX2 code, it also internally uses all known MMX™, Intel® SSE, and Intel® AVX extensions, which are below Intel® AVX2.