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

On 21.07.21 г. 21:45, Linus Torvalds wrote:

On Wed, Jul 21, 2021 at 11:17 AM Nikolay Borisov [off-list ref] wrote:

quoted

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.

quoted

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.