[PATCH v6 4/4] Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537]

[Arjan van de Ven]

On 9/11/2022 1:12 PM, Sunil Pandey wrote:
> On Fri, Nov 12, 2021 at 10:53 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>>
>> On Nov 11 2021, H.J. Lu wrote:
>>
>>> diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
>>> index 57f3f28869..f763cfc7fa 100644
>>> --- a/nptl/pthread_mutex_timedlock.c
>>> +++ b/nptl/pthread_mutex_timedlock.c
>>> @@ -233,12 +233,12 @@ __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
>>>             meantime.  */
>>>          if ((oldval & FUTEX_WAITERS) == 0)
>>>            {
>>> -           if (atomic_compare_and_exchange_bool_acq (&mutex->__data.__lock,
>>> -                                                     oldval | FUTEX_WAITERS,
>>> -                                                     oldval)
>>> -               != 0)
>>> +           int val;
>>> +           if ((val = atomic_compare_and_exchange_val_acq
>>> +                (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
>>> +                 oldval)) != oldval)
>>
>> Please move the assignment out of the condition.
>>
>> Andreas.
>>
>> --
>> Andreas Schwab, schwab@linux-m68k.org
>> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
>> "And now for something completely different."
> 
> I would like to backport this patch to release branch 2.33 and 2.34
> 

what exactly is the stable branch policy that would suggest to backport performance improvements like this ?
(most projects are sticking to "strict bugfixes and other gross oversights" as much as possible)