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

[Will Deacon]

On Thu, Apr 27, 2023 at 09:38:59AM +0000, Bouska, Zdenek wrote:
> > Why is this interrupt handling specific? Just because it's the place
> > where you observed it?
> Yes.
> 
> > So if that helps, then this needs to be addressed globaly and not with
> > some crude hack in the interrupt handling code.
> I just wrote, what helps for me. I didn't mean it as a proposal for merge.
> Sorry for confusion.
> 
> I tried using Will's cpu_relax() implementation [1] everywhere but I was not 
> successful with that yet. ARM64's VDSO makes it complicating and even
> if I left original cpu_relax() just in VDSO, Linux did not boot for me.

It definitely seemed to work when I posted it all those years ago, but I'm
not surprised if it needs some TLC to revive it on more recent kernels.

Will