Re: [PATCH] lib/string: Bring optimized memcmp from glibc

[Nikolay Borisov]

On 21.07.21 г. 21:45, Linus Torvalds wrote:
> On Wed, Jul 21, 2021 at 11:17 AM Nikolay Borisov <nborisov@xxxxxxxx> wrote:
>>
>> I find it somewhat arbitrary that we choose to align the 2nd pointer and
>> not the first.
> 
> Yeah, that's a bit odd, but I don't think it matters.
> 
> The hope is obviously that they are mutually aligned, and in that case
> it doesn't matter which one you aim to align.
> 
>> So you are saying that the current memcmp could indeed use improvement
>> but you don't want it to be based on the glibc's code due to the ugly
>> misalignment handling?
> 
> Yeah. I suspect that this (very simple) patch gives you the same
> performance improvement that the glibc code does.

You suspect correctly, perf profile:

30.44%    -29.38%  [kernel.vmlinux]         [k] memcmp

This is only on x86-64 as I don't have other arch handy. But this one is
definitely good.