Re: Dead code in pthread_cond_wait() for spin-wait

[Olivier Dion <odion@efficios.com>]

On Wed, 11 Oct 2023, Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> wrote:
> On 11/10/23 15:30, Olivier Dion via Libc-help wrote:

[...]

>> However, looking at the following snippet in nptl/pthread_cond_wait.c:
>> 
>>  static __always_inline int
>>  __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
>>      clockid_t clockid, const struct __timespec64 *abstime)
>>  {
>>    const int maxspin = 0;
>>    [...]
>>            /* Spin-wait first. [...] */
>> 	   unsigned int spin = maxspin;
>> 	   while (signals == 0 && spin > 0) {
>>              [...]
>>            }
>>    [...]
>>  }
>> 
>
> Afaik it was added a placeholder for future extension, so fell free to
> send a patch to delete it.

[...]

What about making it work instead?  Would this be something to consider?
IMHO it would be worth it.  Having a fast-path that spins instead of
taking the futex directly can greatly impact performance in some cases.

In the meantime, I think it is safe to remove it.  I'll send a patch on
libc-alpha for that.

Thanks,

Olivier
-- 
Olivier Dion
EfficiOS Inc.
https://www.efficios.com