Re:86 GB/s bitpacking with ARM SIMD (single thread)
by crest on Monday October 06, 2025 @06:17AM
(#45489750)
ARMv8A has nice scalar bit (un)packing instructions. I wonder if NEON is really an improvement over those given that ARM cores tend to have few SIMD ports and NEON is just 128 wide.
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Re:86 GB/s bitpacking with ARM SIMD (single thread)
by ashtonsix on Monday October 06, 2025 @10:44AM
(#45491986)
I'm assuming you're referring to BFM/EXTR? NEON absolutely improves here.
The core I developed on (Neoverse V2) has 4 SIMD ports and 6 scalar integer ports, however only 2 of those scalar ports support multicycle integer operations like the insert variant of BFM (essential for scalar packing).
More importantly, NEON progresses 16 elements per instruction instead of 1.