Intel® Math Kernel Library 11.3 Update 4 Developer Guide
Intel MKL provides conditional numerically reproducible results for a code branch determined by the supported instruction set architecture (ISA). The values you can specify for the MKL_CBWR environment variable may have one of the following equivalent formats:
MKL_CBWR="<branch>"
MKL_CBWR="BRANCH=<branch>"
The <branch> placeholder specifies the CNR branch with one of the following values:
|
Value |
Description |
|---|---|
|
AUTO |
CNR mode uses the standard ISA-based dispatching model while ensuring fixed cache sizes, deterministic reductions, and static scheduling |
|
|
CNR mode uses the branch for the following ISA: |
|
COMPATIBLE |
Intel® Streaming SIMD Extensions 2 (Intel® SSE2) without rcpps/rsqrtps instructions |
|
SSE2 |
Intel SSE2 |
|
SSE3 |
DEPRECATED. Intel® Streaming SIMD Extensions 3 (Intel® SSE3). This setting is kept for backward compatibility and is equivalent to SSE2. |
|
SSSE3 |
Supplemental Streaming SIMD Extensions 3 (SSSE3) |
|
SSE4_1 |
Intel® Streaming SIMD Extensions 4-1 (Intel® SSE4-1) |
|
SSE4_2 |
Intel® Streaming SIMD Extensions 4-2 (Intel® SSE4-2) |
|
AVX |
Intel® Advanced Vector Extensions (Intel® AVX) |
|
AVX2 |
Intel® Advanced Vector Extensions 2 (Intel® AVX2) |
When specifying the CNR branch, be aware of the following:
Reproducible results are provided under Reproducibility Conditions.
Settings other than AUTO or COMPATIBLE are available only for Intel processors.
To get the CNR branch optimized for the processor where your program is currently running, choose the value of AUTO or call the mkl_cbwr_get_auto_branch function.
Setting the MKL_CBWR environment variable or a call to an equivalent mkl_set_cbwr_branch function fixes the code branch and sets the reproducibility mode.
If the value of the branch is incorrect or your processor or operating system does not support the specified ISA, CNR ignores this value and uses the AUTO branch without providing any warning messages.
Calls to functions that define the behavior of CNR must precede any of the math library functions that they control.
Settings specified by the functions take precedence over the settings specified by the environment variable.
See the Intel MKL Developer Reference for how to specify the branches using functions.
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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 |