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Date:   Fri, 2 Apr 2021 16:05:54 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Paul Menzel <pmenzel@molgen.mpg.de>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        LKML <linux-kernel@vger.kernel.org>, Song Liu <song@kernel.org>,
        linux-raid@vger.kernel.org, it+linux-x86@molgen.mpg.de
Subject: Re: [regression 5.4.97 =?utf-8?B?4oaSIDUu?= =?utf-8?B?MTAuMjRd?=
 =?utf-8?Q?=3A?= raid6 avx2x4 speed drops from 18429 MB/s to 6155 MB/s
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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