[bernardladenthin]

Summary

• cpu-linux-s390x uses the IBM Z vector unit. Until now the jar was one static, scalar library: GGML_NATIVE=OFF switches VXE off, so no vector code shipped. build-linux-s390x now builds it modular (JLLAMA_BACKEND_DL) with GGML_CPU_ALL_VARIANTS: ggml-cpu-z13 (scalar), -z15 (VXE2) and -z16 (VXE2 + NNPA). ggml loads the best module for the machine. The floor stays z13 and glibc 2.28.
• Patch 0023, two parts.
  • llamafile/sgemm.h includes <vecintrin.h> a second time after ggml-cpu-impl.h. clang's header has no include guard, so ggml-cpu.c failed with "redefinition of 'vec_extract'"; GCC's guard hid the problem. The include came with llamafile: support s390x SIMD instruction set ggml-org/llama.cpp#14273 and is not needed: sgemm.h declares no vector type, and both of its includers include ggml-cpu-impl.h. Removed.
  • Upstream's s390x variant list starts at z15, so a z13/z14 would get no CPU backend at all. The patch adds a scalar z13 module.
  • Not filed upstream.
• CI:
  • A modular build cannot link jllama_test, so the C++ suite moves to the new job test-cpp-linux-s390x (static build, same toolchain, still under qemu). It gates package.
  • c_abi now runs under the toolchain's emulator. There ggml loads the z15 module, because qemu's CPU model has VXE2, so CI runs the vector code too.
  • build-linux-s390x checks that all three modules exist; the configure skips a variant the compiler rejects (z17 with clang 18) without reporting it.

Measured on cfarm191 (IBM z16, LinuxONE, Debian 13)

b11901, Qwen3-0.6B Q4_K_M converted to big-endian, llama-bench -t 4 -p 64 -n 16, two interleaved rounds, t/s:

module	prompt (pp64)	generation (tg16)
z13 (scalar, what 6.0.x shipped)	19.7 – 19.8	13.6 – 13.8
z15	90.0 – 95.5	57.3 – 58.3
z16	82.6 – 88.3	51.9 – 53.9
z16, GCC 14.2 without the patch (comparison)	85.2 – 86.4	44.1 – 53.9

• Module selection: with all three modules ggml loads z16, without it z15, without both z13.
• Correctness, measured with llama-perplexity --kl-divergence against a Q8_0 reference computed on z13:
  • Q4_K_M has a mean KLD of 0.0777 on z13 and 0.0746 on z16. Both are equally far from the reference.
  • z16 against z13 directly: KLD 0.0087. That is about a tenth of what the quantization costs.
  • Q8_0, z16 against z13: KLD 0.0012, same top token in 98.5 %.
• The CI-built 6.1.0-SNAPSHOT jar of run 40400361809 loads on cfarm191 and answers "Paris." with the big-endian model.

Test plan

• Locally with the job's toolchain (Docker: clang-18, binutils-s390x, the manylinux_2_28 s390x sysroot):
  • the modular build produces all three modules; z17 is skipped;
  • c_abi passes under qemu, with CPU : VXE = 1;
  • verify-native-deps.py: 9 libraries, 0 violations (glibc ≤ 2.27, GLIBCXX_3.4.25, CXXABI_1.3.11, the existing allowlist, typeinfo alignment).
• NativeLoadSmoke with the built directory in the UBI 8 OpenJDK 21 image on RHEL 8.10 s390x (qemu): z15 module, patches=…0022,0023.
• check-patches.py (14 patches, 104 hunks, 0 problems; docs/patches.md current), check-natives.py (0 disagreements), buildcheck unit tests 127/127 on Linux, release gate (75 jobs, 0 violations), run scripts parse, publish.yml loads as YAML.
• CI is green on this branch
• After merge: the CI-built modular jar on cfarm191 (TODO.md, "Linux s390x")

Related issues / PRs

The open TODO item "s390x runs scalar" is closed by this PR. Follows #573 (glibc floor) and #577 (typeinfo alignment).

Checklist

• I have read CONTRIBUTING.md and CODE_OF_CONDUCT.md
• My commits follow Conventional Commits (they follow this repository's own message style)
• No security-sensitive changes

🤖 Generated with Claude Code

https://claude.ai/code/session_01DuAkLtHrCTx81vP5Mt4jad

Summary by CodeRabbit

• New Features
  • Linux on IBM Z (s390x) now offers CPU-optimized library variants for z13, z15, and z16. The best available variant is selected automatically at startup, with a scalar baseline available for older systems.
• Documentation
  • Updated platform information to describe s390x shared-library and CPU-module support, automatic variant selection, and measured performance. The documentation also clarifies that macOS continues to use a static library.

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Commits

Reviewing files that changed from the base of the PR and between 6e76156 and 897111c.

Files selected for processing: 2

• CLAUDE.md
• llama/CMakeLists.txt

Files skipped from review as they are similar to previous changes: 1

• CLAUDE.md

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Walkthrough

Linux s390x now builds modular CPU backends for z13, z15, and z16. The workflow checks for the modules and runs C++ tests in a separate qemu job. CMake, dependency checks, patch inventories, and project documentation reflect the modular build.

Changes: Linux s390x modular CPU build

Layer / File(s)	Summary
Add s390x CPU variants llama/patches/0023-ggml-cpu-s390x-variants-build-with-clang-and-a-z13-baseline.patch, llama/CMakeLists.txt	The patch adds a z13 backend, extends the cross-compilation target range, and removes a conditional vecintrin.h include. CMake enables modular Linux s390x builds and permits the C ABI test under an emulator.
Build and test s390x artifacts .github/workflows/publish.yml, .github/buildcheck/nativedeps.py	The build job checks for the z13, z15, and z16 modules. A separate job runs the C++ suite under qemu, and package requires that job. The dependency description reflects the modular libraries.
Document modular s390x support CHANGELOG.md, CLAUDE.md, README.md, TODO.md, docs/patches.md	The documentation and patch inventories describe the CPU modules, build and test setup, and recorded measurements.

Priority: Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant CMake
  participant BuildWorkflow
  participant QemuTestJob
  participant Package
  CMake->>BuildWorkflow: Configure modular CPU backends
  BuildWorkflow->>BuildWorkflow: Check z13, z15, and z16 modules
  QemuTestJob->>Package: Provide required C++ test result

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Possibly related PRs

• bernardladenthin/java-llama.cpp#573: Defines the s390x sysroot and dependency checks used by this modular build.
• bernardladenthin/java-llama.cpp#568: Documents the s390x glibc limitation that the updated build and platform documentation address.
• bernardladenthin/java-llama.cpp#577: Adds s390x typeinfo alignment checks, which the updated documentation describes for multiple libraries.

Suggested reviewers: claude

Merge Risk: Minimal · up to 89711

The modular s390x build, z13 fallback, required artifacts, and qemu-backed tests are wired coherently; no merge-blocking risk is established.

Architecture risk: Low · up to 89711

The change affects 6 systems.

Changed systems: llama, CHANGELOG.md, CLAUDE.md, docs, README.md, TODO.md

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — llama (service) was modified; 2 changed files map to changed impact.
• observed — CHANGELOG.md (service) was modified; 1 changed file maps to changed impact.
• observed — CLAUDE.md (service) was modified; 1 changed file maps to changed impact.
• observed — docs (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in CHANGELOG.md: Adds a changelog entry for modular s390x CPU libraries with z13, z15, and z16 modules and startup selection. It records z16 benchmark results, patch 0023 build and variant-list fixes, and the s390x C++ test job running under qemu.
• observed — Modified behavior in README.md: The platform description now includes Linux s390x with the shared-library and CPU-module layout; s390x is removed from the platforms described as using one static library, leaving that description for macOS.
• observed — Modified behavior in README.md: The cpu-linux-s390x entry now specifies three startup-selected CPU modules (z13, z15, z16) and adds a z16 performance comparison against the scalar library of 6.0.x.
• observed — Modified behavior in TODO.md: The model-backed plain-C smoke note no longer says that s390x remains a static build; it still identifies macOS as static.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title names the main change: modular s390x CPU backends (z13, z15, z16) with patch 0023, and the z16 speedup. The raw summary and PR objectives both center on this change, so the title is clearly …
Docstring Coverage		No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within survi…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title names the main change: modular s390x CPU backends (z13, z15, z16) with patch 0023, and the z16 speedup. The raw summary and PR objectives both center on this change, so the title is clearly related. It is somewhat long at 78 characters, but it is specific and not vague.

Full details: Docstring Coverage

Explanation

No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 1 files. (2 skipped: 2 unsupported.)

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
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0.0% Coverage on New Code
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