Developer Guide

Developer Guide for Intel® oneAPI Math Kernel Library Windows*

ID 766692
Date 11/07/2023
Public

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Document Table of Contents

Instruction Set Specific Dispatching on Intel® Architectures

Intel® oneAPI Math Kernel Library (oneMKL) 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® Streaming SIMD Extensions 4.2 (Intel® SSE4.2) code path on an Intel processor based on Intel® Advanced Vector Extensions 2 (Intel® AVX2). This feature is not available on non-Intel processors.

In some cases, oneMKL 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 theMKL_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_INSTRUCTIONSdispatches 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, oneMKL 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 512 (Intel® AVX-512)

Yes

AVX512_E1

Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with support for Intel® Deep Learning Boost (Intel® DL Boost)

Yes

AVX512_E2

Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with support for Intel® Deep Learning Boost (Intel® DL Boost), EVEX-encoded AES, and Carry-Less Multiplication Quadword instructions

Yes

AVX512_E3

Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with support for Intel® Deep Learning Boost (Intel® DL Boost) and bfloat16

Yes

AVX512_E4

Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with support for INT8, BF16, FP16 (limited) instructions, and Intel® Advanced Matrix Extensions (Intel® AMX) with INT8 and BF16

Yes

AVX512_E5

Intel® Advanced Vector Extensions 512 (Intel® AVX-512) with support for INT8, BF16, FP16 (limited) instructions, and Intel® Advanced Matrix Extensions (Intel® AMX) with INT8, BF16, and FP16

No

AVX2

Intel® Advanced Vector Extensions 2 (Intel® AVX2)

Yes

AVX2_E1

Intel® Advanced Vector Extensions 2 (Intel® AVX-2) with support for Intel® Deep Learning Boost (Intel® DL Boost)

Yes

SSE4_2

Intel® Streaming SIMD Extensions 4.2 (Intel® SSE4.2)

Yes

For more details about the mkl_enable_instructions function, including the argument values, see the Intel® oneAPI Math Kernel Library (oneMKL) Developer Reference.

For example:

  • To turn on automatic CPU-based dispatching of Intel AVX-512 with support of Intel DL Boost, bfloat16, Intel AMX with bfloat16 and 8-bit integer, and FP16 instruction, do one of the following:
    • Call

      mkl_enable_instructions(MKL_ENABLE_AVX512_E4)

    • Set the environment variable:

      set MKL_ENABLE_INSTRUCTIONS=AVX512_E4

  • 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:

      set MKL_ENABLE_INSTRUCTIONS=AVX2

NOTE:

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