Re: [PATCH v4 3/4] locking/qspinlock: Add ARCH_USE_QUEUED_SPINLOCKS_XCHG32

Peter Zijlstra
2021-04-07T16:55:10Z

On Wed, Apr 07, 2021 at 05:52:36PM +0200, Peter Zijlstra wrote:
> On Wed, Apr 07, 2021 at 04:29:12PM +0200, Christoph Müllner wrote:
> > The comparison with sparc64 is not applicable, as sparc64 does not
> > have LL/SC instructions.
>
> Sparc64 has CAS, without hardware fwd progress. It has to do software
> backoff for failed CAS in order to do software fwd progress.

Again, the longer answer is that this applies identically to LL/SC and
I'm sure we actually have (or had) an architecture in tree that did just
that. I just cannot remember which architecture that was.