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skainet-backend-native-cpu: JVM artifact ships no linux-arm64 libskainet_kernels.so → silent ~1000× reference-kernel fallback on ARM Linux

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
58/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
cmake, kotlin, linux
Domain
backend, build-system, performance

Research direction

Start with the skainet-backend-native-cpu native CMake build and the JVM artifact packaging configuration; the issue says CMake already supports aarch64 and identifies the missing native/linux-arm64/libskainet_kernels.so resource. Check how the existing Linux, macOS, and Windows libraries are built and bundled, then determine how CI can build and include the ARM Linux library. Done when the published JVM artifact contains that library and ARM Linux loads a native kernel instead of falling back to the reference decoder.

Written by the indexing model from the issue text.

Description

bug platform skill:native

Problem

The published skainet-backend-native-cpu 0.61.0 JVM artifact bundles libskainet_kernels for linux-x86_64, macos-arm64 and windows-x86_64 only. There is no native/linux-arm64/libskainet_kernels.so, although NativeLibraryLoader already resolves that path ("aarch64", "arm64" -> "arm64").

On a linux-arm64 JVM, the loader finds nothing, so KernelDispatch has no kernel for packed weights and falls back to the reference decoder:

[SKaiNET] KernelDispatch: no kernel registered for matmul (activation=Dense(bytesPerElement=4), weight=BITNET_B1_58, order=ROW_MAJOR); falling back to the decoding reference kernel (~1000x slower). Install a kernel pack (e.g. KernelPacks.install() + FfmRowMajorKernelPack.install()) before the first forward. Further fallbacks are not reported.

Repro

  • Board: Arduino Ventuno Q (QCS8275, 4× Cortex-A78C + 4× A55), Ubuntu 24.04, Temurin 21.0.12.1 (aarch64).
  • SKaiNET-transformers develop @ a92d65e: :llm-apps:skainet-cli:shadowJar.
  • unzip -l skainet-all.jar | grep native/ shows only linux-x86_64, macos-arm64 and windows-x86_64.
  • java --enable-preview --add-modules jdk.incubator.vector -jar skainet-all.jar -m ggml-model-i2_s.gguf -s 32 "The capital of France is" (BitNet b1.58 2B4T): one thread sits in ReferenceMatmulKernel → BitNetB158TensorData.dequantizeBlock, with 0 tokens after 10.5 min.

Workaround (verified)

I cross-built the library from skainet-backends/skainet-backend-native-cpu/native at tag 0.61.0 and added it to the jar:

cmake -S native -B b -DCMAKE_SYSTEM_NAME=Linux -DCMAKE_SYSTEM_PROCESSOR=aarch64 \
      -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc -DCMAKE_BUILD_TYPE=Release
cmake --build b --target skainet_kernels
mkdir -p native/linux-arm64 && cp b/libskainet_kernels.so native/linux-arm64/
jar uf skainet-all.jar native/linux-arm64/libskainet_kernels.so

With that, the same run produces correct greedy output at 1.6–1.8 tok/s instead of the reference fallback.

Ask

  • Build and bundle native/linux-arm64/libskainet_kernels.so in the JVM artifact. The CMake file already handles aarch64 cross builds (-march=armv8.2-a+fp16+dotprod, with NeoGPU pinned to armv8-a). A CI job using gcc-aarch64-linux-gnu or an arm64 runner would cover it.
  • Consider making the "no kernel registered → reference fallback" message an error on platforms where a native pack is expected, or at least naming the missing resource path.

Related: #920 (mobile/Apple/Android JNI; this issue is the plain linux-arm64 JVM case: Raspberry Pi, Qualcomm IoT boards, Graviton).

Dominant language
Kotlin
Stars
52
Forks
15
Avg merge
1d 10h
Merged PRs (30d)
59

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