Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks

Nicholas Piggin
2020-07-23T16:12:21Z

Excerpts from Waiman Long's message of July 24, 2020 12:29 am:
> On 7/23/20 9:30 AM, Nicholas Piggin wrote:
>>> I would prefer to extract out the pending bit handling code out into a
>>> separate helper function which can be overridden by the arch code
>>> instead of breaking the slowpath into 2 pieces.
>> You mean have the arch provide a queued_spin_lock_slowpath_pending
>> function that the slow path calls?
>>
>> I would actually prefer the pending handling can be made inline in
>> the queued_spin_lock function, especially with out-of-line locks it
>> makes sense to put it there.
>>
>> We could ifdef out queued_spin_lock_slowpath_queue if it's not used,
>> then __queued_spin_lock_slowpath_queue would be inlined into the
>> caller so there would be no split?
>
> The pending code is an optimization for lightly contended locks. That is
> why I think it is appropriate to extract it into a helper function and
> mark it as such.
>
> You can certainly put the code in the arch's spin_lock code, you just
> has to override the generic pending code by a null function.

I see what you mean. I guess that would work fine.

Thanks,
Nick