Re: Improving spin-lock implementation on ARM.

On Sat, Nov 28, 2020 at 5:36 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> So at least on Apple's hardware, it seems like the CAS
> implementation might be a shade faster when uncontended,
> but it's very clearly worse when there is contention for
> the spinlock. That's interesting, because the argument
> that CAS should involve strictly less work seems valid ...
> but that's what I'm getting.
>
> It might be useful to try this on other ARM platforms,
> but I lack the energy right now (plus the only other
> thing I've got is a Raspberry Pi, which might not be
> something we particularly care about performance-wise).

I guess that might depend on the implementation of CAS and TAS. I bet
usage of CAS in spinlock gives advantage when ldxr/stxr are used, but
not when swpal/casa are used. I found out that I can force clang to
use swpal/casa by setting "-march=armv8-a+lse". I'm going to make
some experiments on a multicore AWS graviton2 instance with different
atomic implementation.

------
Regards,
Alexander Korotkov