linux benchmarks on Skylake-SP severly broken without glibc >= 2.26

hfp

New Member
Nov 24, 2017
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Hello,

as a new user of Skylake-SP I noticed very poor performance compiling linux kernels compared to expected numbers. Using the i7z tool I found that during compile all cores went down to "AVX2 heavy" turbo frequencies. After some investigations I found that you need at least 2 commits from glibc 2.26 to avoid non-helpful use of AVX512 load/stores that will cause the CPU to limit to "AVX2 heavy" turbo frequencies.

Patches:
sourceware.org Git - glibc.git/commit
sourceware.org Git - glibc.git/commit

@Patrick Could you please verify on your machines if you were not using glibc >= 2.26?

Regards Andreas