linux-kernel - Re: [GIT PULL] x86/misc for 6.5

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Date:   Tue, 27 Jun 2023 15:50:48 -0700
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Noah Goldstein <goldstein.w.n@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86/misc for 6.5

On 6/27/2023 3:43 PM, Linus Torvalds wrote:
> On Tue, 27 Jun 2023 at 15:25, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> I don't know what the rules are - and some of the functions you test
>> seem actively buggy (ie not handling alignment right etc).
> 
> Oh. And you *only* test the 40-byte case. That seems a bit bogus.
> 
> If I change the packet size from 40 to 1500, I get
> 
>    02: 185.1 / 186.4 cycles (8b414316) Upcoming linux kernel version
>    04: 184.9 / 186.5 cycles (8b414316) Specialized to size 40
>    06: 107.3 / 117.2 cycles (8b414316) New version
>    22: 185.6 / 186.5 cycles (8b414316) Odd-alignment handling removed
> 
> which seems unexpectedly bad for the other versions.
> 

I'm not surprised though; running 2 parallel streams (where one stream has a fixed zero as input,
so can run OOO any time) .. can really have a performance change like this