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

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 <[email protected]>
>>>
>>> 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.