Overhead of arm64 LSE per-CPU atomics?

[Catalin Marinas]

On Sat, Nov 01, 2025 at 07:41:02PM +0800, Yicong Yang wrote:
> FYI, there's a version to allow prefetech added prior to LSE
> opertaions by one boot option [1], if we want to reconsidered in this
> way, it's more flexible and can be controlled by the OS without
> touching the system configurations (may need to update the firmware).

I'm against adding boot time options for this. We either add them
permanently if beneficial for most microarchitectures or we get back to
the hardware people to ask for improvements (or, potentially, imp def
configurations like we have on a few of the Arm Ltd implementations).

> But need to add the prefetch in per-cpu implementation as you've
> noticed above (didn't add it since no prefetch for LL/SC
> implementation there, maybe a missing?)

Maybe no-one stressed these to notice any difference between LL/SC and
LSE.

-- 
Catalin