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ggml-cpu: skip x86 variants whose register state the OS has not enabled - #246
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The CPU backend score checked CPUID feature bits only. On a machine where CPUID advertises AVX-512 but the OS leaves the ZMM state off in XCR0 (seen on Zen 5 Windows, XCR0 = 0x7), the cascadelake variant won and the first 512-bit instruction raised an illegal-instruction fault. Read XCR0 with xgetbv when OSXSAVE is set and score a variant 0 unless the OS enables the state it needs: SSE+YMM for AVX-class variants, opmask+ZMM for AVX-512, XTILECFG+XTILEDATA for AMX. Scores are otherwise unchanged. Fixes cjpais/Handy#2402. Co-Authored-By: Claude Fable 5.1 <[email protected]>
ggml/ is regenerated by scripts/sync-ggml.sh from the upstream SHA plus patches/ggml/*.patch; without a patch file the cpu-feats.cpp fix would be dropped on the next sync. Co-Authored-By: Claude Fable 5.1 <[email protected]>
macOS enables AVX-512 register state lazily, so XCR0 bits 5-7 are clear until a thread first uses AVX-512. The XCR0 check therefore rejected the AVX-512 variants on Intel Macs that support them. On Apple, take AVX-512 OS support from hw.optional.avx512f instead, as google/cpu_features does. Also mark `is` unused for the x64 variant, which checks no CPUID bits and otherwise warns under -Wextra. Patch 0004 regenerated to match.
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…ter#246's 0004 Co-Authored-By: Claude Opus 5.5 <[email protected]>
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Summary
Handy no longer fails to load any model on newer AMD processors where Windows hasn't switched on the chip's advanced math features.
ggml_backend_cpu_x86_score()only checks CPUID, so it picksggml-cpu-cascadelake.dll; the first 512-bit instruction faults (0xC000001D).xgetbvwhen OSXSAVE is set, and score a variant 0 if the OS hasn't enabled the state it needs (YMM for AVX, opmask + ZMM for AVX-512, tiles for AMX).Scope
ggml/src/ggml-cpu/arch/x86/cpu-feats.cpp: the fix.patches/ggml/0004-cpu-x86-score-os-xsave-check.patch+ggml/UPSTREAM: same change as a downstream patch sosync-ggml.shkeeps it.Related
Fixes cjpais/Handy#2402. Measurements from
fakingpescobar-ctrlin that issue.Not fixed in llama.cpp master yet; open PRs there: ggml-org/llama.cpp#19514, #20388, #20940.
AI Assistance
Code written with Claude Code; I reviewed it.
Validation
Harness compiling patched and original
cpu-feats.cppper variant (MSVC 2022, sameGGML_*defines), with XCR0 injected:alderlake(waszen4).sse42.git apply --check, forward and reverse.Not run: full library build, repo tests, GCC/Clang
xgetbvpath, real Zen 5 hardware.🤖 Generated with Claude Code