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Subject: Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks
To:     Nicholas Piggin <npiggin@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>
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        Will Deacon <will@kernel.org>
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From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
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Date:   Thu, 23 Jul 2020 10:29:05 -0400
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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.

Cheers,
Longman