86 GB/s bitpacking with ARM SIMD (single thread)

Re:86 GB/s bitpacking with ARM SIMD (single thread) by ashtonsix on Sunday October 05, 2025 @10:21AM (#45481702)

Thank you so much for attempting a reproduction! (I posted this on Reddit and most commenters didn't even click the link)

For the baseline you need SIMDe headers: https://github.com/simd-everywhere/simde/tree/master/simde. These alias x86 intrinsics to ARM intrinsics. The baseline is based on the previous State-of-The-Art (https://arxiv.org/abs/1209.2137) which happens to be x86-based; using SIMDe to compile was the highest-integrity way I could think of to compare with the previous SOTA.

Note: M1 chips specifically have notoriously bad small-shift performance, so the benchmark results will be very bad on your machine. M3 partially fixed this, M4 fixed completely. My primary target is server-class rather than consumer-class hardware so I'm not too worried about this.

The benchmark results were cpy-pasted from the terminal. The README prose was AI generated from my rough notes (I'm confident when communicating with other experts/researchers, but less-so with communication to a general audience).

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Re:86 GB/s bitpacking with ARM SIMD (single thread) by ozgrakkurt on Sunday October 05, 2025 @01:05PM (#45483247)

Super cool!

Pretty sure anyone going into this kind of post about simd would prefer your writing to llm

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Re:86 GB/s bitpacking with ARM SIMD (single thread) by deadmutex on Sunday October 05, 2025 @06:40PM (#45485926)

Here is a repro using GCE's C4A Axion instances (c4A-highcpu-72). Seems to beat Graviton? Maybe the title of the thread can be updated to a larger number :) ? I used the largest instance to avoid noisy neighbor issues.

  $ ./out/bytepack_eval
  Bytepack Bench — 16 KiB, reps=20000 (pinned if available)
  Throughput GB/s

  K  NEON pack   NEON unpack  Baseline pack   Baseline unpack
  1  94.77       84.05        45.01           63.12          
  2  123.63      94.74        52.70           66.63          
  3  94.62       83.89        45.32           68.43          
  4  112.68      77.91        58.10           78.20          
  5  86.96       80.02        44.32           60.77          
  6  93.50       92.08        51.22           67.20          
  7  87.10       79.53        43.94           57.95          
  8  90.49       92.36        68.99           83.88

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Re:86 GB/s bitpacking with ARM SIMD (single thread) by ashtonsix on Monday October 06, 2025 @05:53AM (#45489606)

Oh nice! Axion C4A and Graviton4 use the same core (Neoverse V2), so the performance difference is due to factors like clock speed and power management.

I used a geometric mean to calculate the top-line "86 GB/s" for NEON pack/unpack; so that's 91 GB/s for the C4A repro. Probably going to leave the title unmodified.

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