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LocalAI/backend/Dockerfile.ds4
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Claudio Maradonna 9e831d7709 fix(ds4): build CUDA kernels for the target architecture (#11840)
* fix(ds4): build CUDA kernels for the target architecture

The ds4 backend compiled its CUDA objects with no -arch. Upstream's Makefile
leaves CUDA_ARCH empty and its `cuda` target refuses to build without one,
offering `cuda-spark` (sm_121) and `cuda-generic` (native) instead. We invoke
its object targets directly, which bypasses that guard, so nvcc fell back to
its default architecture and the kernels ran as JIT'd PTX on the real GPU.

On GB10 (sm_121) that silently corrupted inference: any prompt over roughly 128
tokens produced text unrelated to the input and never closed its thinking
block, so content came back empty and the chat showed only reasoning; longer
prompts failed with "cuda decode failed". It also cost close to two orders of
magnitude of prefill throughput. Measured on one box, same model, same prompt,
same GPU, upstream ds4 at the pinned commit, differing only in the nvcc flags:

  make -B ds4      (archless, as we build it)   garbage output    4.21 t/s
  make cuda-spark  (compute_121a/sm_121a)       correct output  325.70 t/s

Select an architecture list from CUDA_MAJOR_VERSION, which the backend matrix
already declares for both ds4 cublas entries but Dockerfile.ds4 never forwarded.
Upstream's CUDA_ARCH takes a single value, so it cannot express the fat binary
these images need; NVCC_ARCH_FLAGS is overridden instead, since a command-line
assignment wins over its `:=`. The lists are copied from vllm-cpp rather than
invented so the two CUDA images cover the same GPUs, with l4t/arm64 covering
Orin, Thor and GB10. An empty CUDA_MAJOR_VERSION keeps upstream's `native`
behaviour for local developer builds, and no CI runner has a GPU to enumerate.

DS4_CUDA_HAVE_MXF4 is deliberately left unset: upstream defines it only for
single-arch sm_120/sm_121 builds and guards it with a plain #ifdef rather than
__CUDA_ARCH__, so it cannot be combined with older archs. It gates an optional
MXFP4 indexer fast path whose #ifndef branch returns 0 and falls back cleanly,
so omitting it costs speed on GB10, not correctness.

Assisted-by: Claude Code:claude-opus-5
Signed-off-by: Claudio Maradonna <git@codeshifter.xyz>

* test(ds4): cover the multi-batch prefill regression

The architecture fix has no automated guard: every existing e2e spec uses a
short prompt, and the miscompiled backend answered short prompts correctly.
The corruption only appears once a prompt spans more than one prefill batch,
so the whole suite passed against a backend that produced garbage in normal
use.

Add an opt-in "long_prefill" capability to the backend e2e suite that sends a
prompt well past one batch with a known needle and asserts the answer still
reflects it, and document in the ds4 guide why the build must never omit an
nvcc architecture, how to check which flags a configuration resolves to
without compiling, and how to run the new spec.

Assisted-by: Claude Code:claude-opus-5
Signed-off-by: Claudio Maradonna <git@codeshifter.xyz>

---------

Signed-off-by: Claudio Maradonna <git@codeshifter.xyz>
2026-09-03 13:03:44 +02:00

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1.7 KiB
Docker

ARG BASE_IMAGE=ubuntu:24.04
ARG APT_MIRROR=""
ARG APT_PORTS_MIRROR=""
# BASE_IMAGE is either ubuntu:24.04 (for cpu builds) or nvidia/cuda:13.0.0-devel-ubuntu24.04
# (for cublas builds). Both ship apt + Ubuntu Noble packages; the nvidia/cuda base
# additionally provides /usr/local/cuda. Darwin (Metal) builds bypass this Dockerfile
# entirely via scripts/build/ds4-darwin.sh.
FROM ${BASE_IMAGE} AS builder
ARG BUILD_TYPE
ARG TARGETARCH
ARG TARGETVARIANT
ARG CUDA_MAJOR_VERSION
ENV BUILD_TYPE=${BUILD_TYPE} \
DEBIAN_FRONTEND=noninteractive \
PATH=/usr/local/cuda/bin:${PATH}
WORKDIR /build
# Install build-time deps via plain apt - install-base-deps.sh's full pipeline
# (CUDA keyring + from-source gRPC) is unnecessary here:
# - CUDA: when BASE_IMAGE=nvidia/cuda:*, /usr/local/cuda is already populated;
# for the cpu build we don't need CUDA at all.
# - gRPC/Protobuf: system apt packages are sufficient; ds4's wrapper only links
# against them, it doesn't ship the gRPC source tree.
# - nlohmann-json: dsml_renderer's only third-party dep.
RUN apt-get update && \
apt-get install -y --no-install-recommends \
git cmake build-essential pkg-config ca-certificates \
libgrpc++-dev libprotobuf-dev protobuf-compiler protobuf-compiler-grpc \
nlohmann-json3-dev && \
apt-get clean && \
rm -rf /var/lib/apt/lists/*
COPY . /LocalAI
RUN --mount=type=cache,target=/root/.ccache,id=ds4-ccache-${TARGETARCH}-${BUILD_TYPE},sharing=locked \
make -C /LocalAI/backend/cpp/ds4 BUILD_TYPE=${BUILD_TYPE} \
CUDA_MAJOR_VERSION=${CUDA_MAJOR_VERSION} NATIVE=false grpc-server package
FROM scratch
COPY --from=builder /LocalAI/backend/cpp/ds4/package/. ./