Re: [PATCH v1 1/1] s390: mm: convert pgste locking functions to C

Alexander Gordeev
2023-12-06T13:14:32Z

On Wed, Dec 06, 2023 at 10:15:41AM +0100, Heiko Carstens wrote:
> On Wed, Dec 06, 2023 at 10:01:18AM +0100, Alexander Gordeev wrote:
> > On Tue, Dec 05, 2023 at 06:32:52PM +0100, Claudio Imbrenda wrote:
> > ...
> > > + do {
> > > + value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);
> >
> > Would it make sense to cpu_relax() here, e.g with a follow-up patch?
>
> No, because cpu_relax() is a no-op on our architecture (besides that it
> translates to barrier(); but __atomic64_or_barrier() obviously comes also
> with barrier() semantics).
>
> We used to do diag 0x44 with cpu_relax() but that caused many performance
> problems, therefore we removed diag 0x44 completely from the kernel quite
> some time ago.
>
> See also commit 1b68ac8678a8 ("s390: remove last diag 0x44 caller").

Thanks for the clarification!

Applied.