Re: [PATCH v3] Avoid memory barrier in read_seqcount() through load acquire

[Linus Torvalds]

On Wed, 18 Sept 2024 at 08:22, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, 18 Sept 2024 at 13:15, Christoph Lameter (Ampere) <cl@xxxxxxxxxx> wrote:
> >
> > Other arches do not have acquire / release and will create additional
> > barriers in the fallback implementation of smp_load_acquire. So it needs
> > to be an arch config option.
>
> Actually, I looked at a few cases, and it doesn't really seem to be true.

Bah. I ended up just committing the minimal version of this all. I
gave Christoph credit for the commit, because I stole his commit
message, and he did most of the work, I just ended up going "simplify,
simplify, simplify".

I doubt anybody will notice, and smp_load_acquire() is the future. Any
architecture that does badly on it just doesn't matter (and, as
mentioned, I don't think they even exist - "smp_rmb()" is generally at
least as expensive).

                 Linus