From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks
Date: Fri, 24 Jul 2020 02:12:21 +1000
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To: Waiman Long <longman@redhat.com>, Peter Zijlstra <peterz@infradead.org>
Cc: Anton Blanchard <anton@ozlabs.org>, Boqun Feng <boqun.feng@gmail.com>, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Ingo Molnar <mingo@redhat.com>, virtualization@lists.linux-foundation.org, Will Deacon <will@kernel.org>
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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?
>=20
> The pending code is an optimization for lightly contended locks. That is=20
> why I think it is appropriate to extract it into a helper function and=20
> mark it as such.
>=20
> You can certainly put the code in the arch's spin_lock code, you just=20
> has to override the generic pending code by a null function.

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

Thanks,
Nick