Developer Guide

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Instruction Set Specific Dispatching on Intel® Architectures

Intel® oneAPI Math Kernel Library
automatically queries and then dispatches the code path supported on your Intel® processor to the optimal instruction set architecture (ISA) by default. The
MKL_ENABLE_INSTRUCTIONS
environment variable or the
mkl_enable_instructions
support function enables you to dispatch to an ISA-specific code path of your choice. For example, you can run the Intel® Advanced Vector Extensions (Intel® AVX) code path on an Intel processor based on Intel® Advanced Vector Extensions 2 (Intel® AVX2), or you can run the Intel® Streaming SIMD Extensions 4.2 (Intel® SSE4.2) code path on an Intel AVX-enabled Intel processor. This feature is not available on non-Intel processors.
In some cases
Intel® oneAPI Math Kernel Library
also provides support for upcoming architectures ahead of hardware availability, but the library does not automatically dispatch the code path specific to an upcoming ISA by default. If for your exploratory work you need to enable an ISA for an Intel processor that is not yet released or if you are working in a simulated environment, you can use the
MKL_ENABLE_INSTRUCTIONS
environment variable or
mkl_enable_instructions
support function.
The following table lists possible values of
MKL_ENABLE_INSTRUCTIONS
alongside the corresponding ISA supported by a given processor.
MKL_ENABLE_INSTRUCTIONS
dispatches to the default ISA if the ISA requested is not supported on the particular Intel processor. For example, if you request to run the Intel AVX512 code path on a processor based on Intel AVX2,
Intel® oneAPI Math Kernel Library
runs the Intel AVX2 code path. The table also explains whether the ISA is dispatched by default on the processor that supports this ISA.
Value of
MKL_ENABLE_INSTRUCTIONS
ISA
Dispatched by Default
AVX512
Intel® Advanced Vector Extensions (Intel® AVX-512) for systems based on Intel® Xeon® processors
Yes
AVX512_E1
Intel® Advanced Vector Extensions (Intel® AVX-512) with support for Vector Neural Network Instructions.
Yes
AVX512_E2
ICX: Intel® Advanced Vector Extensions (Intel® AVX-512) enabled processors.
Yes
AVX512_E3
Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with support of Vector Neural Network Instructions supporting BF16 enabled processors.
Yes
AVX512_E4
Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with Intel® Deep Learning Boost (Intel® DL Boost) and bfloat16 support and Intel® Advanced Matrix Extensions (Intel® AMX) with bfloat16 and 8-bit integer support.
No
AVX2
Intel® AVX2
Yes
AVX2_E1
Intel® Advanced Vector Extensions 2 (Intel® AVX2) with support for Intel® Deep Learning Boost (Intel® DL Boost).
No
AVX
Intel® AVX
Yes
SSE4_2
Intel® SSE4.2
Yes
For more details about the
mkl_enable_instructions
function, including the argument values, see the
Intel® oneAPI Math Kernel Library
Developer Reference
.
For example:
  • To configure the library not to dispatch more recent architectures than Intel AVX2, do one of the following:
    • Call
      mkl_enable_instructions(MKL_ENABLE_AVX2)
    • Set the environment variable:
      • For the bash shell:
        export MKL_ENABLE_INSTRUCTIONS=AVX2
      • For a C shell (csh or tcsh):
        setenv MKL_ENABLE_INSTRUCTIONS AVX2
Settings specified by the
mkl_enable_instructions
function take precedence over the settings specified by the
MKL_ENABLE_INSTRUCTIONS
environment variable.
Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.
Notice revision #20201201

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.