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Arm’s SVE2 Enables Shift From Neon

October 27, 2020

Author: Aakash Jani

Arm’s second-generation Scalable Vector Extension (SVE2) will enable a transition from the decade-old Neon technology, lifting SIMD performance in smartphones. Although the company has announced its first CPU based on the original SVE, that version lacks some of Neon’s capabilities. Like its predecessor, SVE2 supports vector widths from 128 to 2,048 bits and facilitates vector-length-agnostic programming, but it adds features that allow it to fully replace the well established Neon.

SVE2’s new features target computer vision, cryptography, digital signal processing, and similar tasks. Although SVE2 is a superset of SVE, it adds certain Neon-like instructions. Other new features extend or add capabilities that enable the compiler to vectorize general-purpose operations, such as down-counting loops and compare operations. In combination with the new technology, Arm announced its Transactional Memory Extension (TME), which ensures the coherence and sovereignty of critical memory regions while improving throughput by linearizing memory transactions and implementing memory locks.

Compared with 2x 128-bit Neon units, a 256-bit SVE2 design boosts performance by an average of 85% across a variety of benchmarks. Most of the performance boost, however, comes from new matrix-multiplication operations, which are important for DSP calculations. Thus, the gains vary widely depending on how frequently these operations appear.

The British intellectual-property (IP) licensor has released an SVE2 ISA manual and guides that show software developers how to work with the new extensions. Developers will be able to test SVE2 on Arm’s in-house emulator, or they can use an open-source emulator such as Qemu. GCC 10, LLVM Clang 9.0, and other leading open-source compilers already support the technology. The company hasn’t disclosed any cores that implement SVE2. We expect the first chips using SVE2-enabled Cortex CPU cores to reach production in late 2022, but these cores will likely retain Neon compatibility for several more years.

Subscribers can view the full article in the Microprocessor Report.

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