On Fri, Apr 02, 2021 at 10:33:51AM +0200, Paul Menzel wrote:

Dear Linux folks,


On an two socket AMD EPYC 7601, we noticed a decrease in raid6 avx2x4 speed
shown at the beginning of the boot.

                       5.4.95        5.10.24
----------------------------------------------
raid6: avx2x4 gen()   18429 MB/s     6155 MB/s
raid6: avx2x4 xor()    6644 MB/s     4274 MB/s
raid6: avx2x2 gen()   17894 MB/s    18744 MB/s
raid6: avx2x2 xor()   11642 MB/s    11950 MB/s
raid6: avx2x1 gen()   13992 MB/s    17112 MB/s
raid6: avx2x1 xor()   10855 MB/s    11143 MB/s

Looks like those two might help:

49200d17d27d x86/fpu/64: Don't FNINIT in kernel_fpu_begin()
e45122893a98 x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette