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From: "mikulas at artax dot karlin.mff.cuni.cz" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug string/31675] New: glibc.cpu.hwcaps doesn't work as documented Date: Tue, 23 Apr 2024 18:11:21 +0000 [thread overview] Message-ID: <bug-31675-131@http.sourceware.org/bugzilla/> (raw) https://sourceware.org/bugzilla/show_bug.cgi?id=31675 Bug ID: 31675 Summary: glibc.cpu.hwcaps doesn't work as documented Product: glibc Version: 2.37 Status: UNCONFIRMED Severity: normal Priority: P2 Component: string Assignee: unassigned at sourceware dot org Reporter: mikulas at artax dot karlin.mff.cuni.cz Target Milestone: --- If I disable AVX512 and AVX2 with "export GLIBC_TUNABLES=glibc.cpu.hwcaps=-AVX512F,-AVX2,-AVX512VL", glibc uses __memcpy_avx_unaligned_erms version of memcpy that uses AVX2 instructions. We need to add "AVX_Fast_Unaligned_Load" to suppress AVX2. If I set: "export GLIBC_TUNABLES=glibc.cpu.hwcaps=-AVX512F,-AVX2,-AVX512VL,-AVX_Fast_Unaligned_Load", then glibc will use the SSE3 version of memcpy. The need to set "AVX_Fast_Unaligned_Load" should be either documented or fixed. The documentation says "The glibc.cpu.hwcaps=-xxx,yyy,-zzz... tunable allows the user to enable CPU/ARCH feature yyy, disable CPU/ARCH feature xxx and zzz where the feature name is case-sensitive and has to match the ones in sysdeps/x86/include/cpu-features.h.", but the file "cpu-features.h" doesn't contain "AVX_Fast_Unaligned_Load". -- You are receiving this mail because: You are on the CC list for the bug.
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