CPU and AVX

What is AVX, and why does it matter?

AVX (Advanced Vector Extensions) is a set of CPU instructions for accelerating numerical computations. See Wikipedia for more details.

Note that AVX only applies to nd4j-native (CPU) backend for x86 devices, not GPUs and not ARM/PPC devices.

Why AVX matters: performance. You want to use the version of ND4J compiled with the highest level of AVX supported by your system.

AVX support for different CPUs - summary:

• Most modern x86 CPUs: AVX2 is supported

• Some high-end server CPUs: AVX512 may be supported

• Old CPUs (pre 2012) and low power x86 (Atom, Celeron): No AVX support (usually)

Note that CPUs supporting later versions of AVX include all earlier versions also. This means it's possible run a generic x86 or AVX2 binary on a system supporting AVX512. However it is not possible to run binaries built for later versions (such as avx512) on a CPU that doesn't have support for those instructions.

In version 1.0.0-beta6 and later you may get a warning as follows, if AVX is not configured optimally:

*********************************** CPU Feature Check Warning ***********************************
Warning: Initializing ND4J with Generic x86 binary on a CPU with AVX/AVX2 support
Using ND4J with AVX/AVX2 will improve performance. See deeplearning4j.org/cpu for more details
Or set environment variable ND4J_IGNORE_AVX=true to suppress this warning
************************************************************************************************

Configuring AVX in ND4J/DL4J

As noted earlier, for best performance you should use the version of ND4J that matches your CPU's supported AVX level.

ND4J defaults configuration (when just including the nd4j-native or nd4j-native-platform dependencies without maven classifier configuration) is "generic x86" (no AVX) for nd4j/nd4j-platform dependencies.

To configure AVX2 and AVX512, you need to specify a classifier for the appropriate architecture.

The following binaries (nd4j-native classifiers) are provided for x86 architectures:

• Generic x86 (no AVX): linux-x86_64, windows-x86_64, macosx-x86_64

• AVX2: linux-x86_64-avx2, windows-x86_64-avx2, macosx-x86_64-avx2

• AVX512: linux-x86_64-avx512

Example: Configuring AVX2 on Windows (Maven pom.xml)

<dependency>
    <groupId>org.nd4j</groupId>
    <artifactId>nd4j-native</artifactId>
    <version>${nd4j.version}</version>
</dependency>

<dependency>
    <groupId>org.nd4j</groupId>
    <artifactId>nd4j-native</artifactId>
    <version>${nd4j.version}</version>
    <classifier>windows-x86_64-avx2</classifier>
</dependency>

Example: Configuring AVX512 on Linux (Maven pom.xml)

<dependency>
    <groupId>org.nd4j</groupId>
    <artifactId>nd4j-native</artifactId>
    <version>${nd4j.version}</version>
</dependency>

<dependency>
    <groupId>org.nd4j</groupId>
    <artifactId>nd4j-native</artifactId>
    <version>${nd4j.version}</version>
    <classifier>linux-x86_64-avx512</classifier>
</dependency>

Note that you need both nd4j-native dependencies - with and without the classifier.

In the examples above, it is assumed that a Maven property nd4j.version is set to an appropriate ND4J version such as 1.0.0-beta6