[PATCH] S390: Remove support for lock elision.

[Stefan Liebler]

On 7/3/25 14:34, Adhemerval Zanella Netto wrote:
> 
> 
> On 03/07/25 04:06, Stefan Liebler wrote:
>> On 7/2/25 17:53, Adhemerval Zanella Netto wrote:
>>>
>>>
>>> On 01/07/25 06:39, Stefan Liebler wrote:
>>>> The support for TX lock elision of pthread mutexes on s390x is now removed.
>>>>
>>>> As already announced back in 2022 with z16, the used non-constrained
>>>> transactions are now not usable anymore on z17
>>>> (https://www.ibm.com/support/pages/system/files/inline-files/Tech%20Bytes%20May%202025%20zVM%207.4%20and%20IBM%20z17.pdf):
>>>> z16 Statement of Direction:
>>>> Removal of support of the transactional execution and constrained transactional
>>>> execution facility: In a future IBM Z hardware system family, the transactional
>>>> execution and constrained transactional execution facility will no longer be
>>>> supported.  Users of the facility on current servers should always check the
>>>> facility indications before use.
>>>>
>>>> z17 Support:
>>>> Reduced support for transactional execution (TX) - Non-constrained transactions
>>>> will result in unconditionally aborting with condition code 1 (CC1) and no TDB
>>>> stored.
>>>
>>> I wonder if we still want to support it for x86 and powerpc.  If I
>>> recall correctly, x86 results are mixed and on some chips TSX was
>>> disabled in firmware to avoid some odd issues.  On POWER the kernel
>>> added PPC_FEATURE2_HTM_NOSC to avoid some odd ssues as well.
>>>
>> Good question, but I can only decide it for s390x. Therefore this patch
>> only covers s390x.
>> Nevertheless, I've added the powerpc / x86_64 maintainers. Perhaps they
>> can decide for power and x86_64.
> 
> When I added support for powerpc it was more to add feature parity with
> x86 and to add a way to explore HTM/LE with pthreads.  However, I have
> not heard any project that actively uses, nor any performance benefits
> of using it along pthread. 

As there is currently no response regarding removal of lock elision also
for power and x86_64, if nobody opposes, I would like to commit the
removal of lock elision support for s390x in a few days.

@Andreas Hüttel: Is this fine for you regarding the release?

Bye,
Stefan