Re: Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in interrupt handling

Thomas Gleixner
2023-04-26T21:30:20Z

On Wed, Apr 26 2023 at 12:03, Zdenek Bouska wrote:
> following patch is my current approach for fixing this issue. I introduced
> big_cpu_relax(), which uses Will's implementation [1] on ARM64 without
> LSE atomics and original cpu_relax() on any other CPU.

Why is this interrupt handling specific? Just because it's the place
where you observed it?

That's a general issue for any code which uses atomics for forward
progress. LL/SC simply does not guarantee that.

So if that helps, then this needs to be addressed globaly and not with
some crude hack in the interrupt handling code.

> Anyone has a better idea how to solve this issue properly?

Use hardware with LSE atomics :)

Thanks,

tglx