Re: [PATCH v4 12/17] s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS

[Shrikanth Hegde]

Hi Peter.

On 8/5/26 3:12 PM, Peter Zijlstra wrote:
> On Wed, Aug 05, 2026 at 01:57:04AM +0530, Shrikanth Hegde wrote:
> > +maddy, christophe,
> >
> > On 8/4/26 9:44 PM, Boqun Feng wrote:
> > > From: Heiko Carstens <hca@xxxxxxxxxxxxx>
> > >
> > > Convert s390's preempt_count to 64 bit, and change the preempt
> > > primitives accordingly.
> >
> > > +	union {
> > > +		struct {
> > > +			__u32	need_resched;	/* 0x03a8 */
> > > +			__u32	count;		/* 0x03ac */
> > > +		} preempt;
> > > +		__u64	preempt_count;		/* 0x03a8 */
> > > +	};
> >
> >
> > This is interesting. So arm64, s390 will have similar implementation
> > w.r.t to preempt_count.
> >
> > I guess PoC that i was trying for ppc64 is worth pursuing even more,
> > since ppc64 is one missing major arch which still uses old method
> > of querying tif_need_resched.
> > With similar change ppc64 can set HAS_SEPARATE_PREEMPT_RESCHED_BITS too.
>
> Yes. PPC should be able to the same thing ARM64 does.

Yes. I am thinking of moving it to PACA instead of keeping it in thread_info
as PACA is a natural per-CPU storage.

If i hit any major hurdle there, will use thread info similar to arm64.