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Message-ID: <2899b471-b009-4bb5-bc81-19a8b8c9c955@redhat.com>
Date: Fri, 29 Dec 2023 21:54:48 -0500
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Subject: Re: [PATCH next 3/5] locking/osq_lock: Clarify osq_wait_next()
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To: David Laight <David.Laight@ACULAB.COM>,
 "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
 "'peterz@infradead.org'" <peterz@infradead.org>
Cc: "'mingo@redhat.com'" <mingo@redhat.com>,
 "'will@kernel.org'" <will@kernel.org>,
 "'boqun.feng@gmail.com'" <boqun.feng@gmail.com>,
 'Linus Torvalds' <torvalds@linux-foundation.org>,
 "'xinhui.pan@linux.vnet.ibm.com'" <xinhui.pan@linux.vnet.ibm.com>,
 "'virtualization@lists.linux-foundation.org'"
 <virtualization@lists.linux-foundation.org>,
 'Zeng Heng' <zengheng4@huawei.com>
References: <73a4b31c9c874081baabad9e5f2e5204@AcuMS.aculab.com>
 <7c8828aec72e42eeb841ca0ee3397e9a@AcuMS.aculab.com>
From: Waiman Long <longman@redhat.com>
In-Reply-To: <7c8828aec72e42eeb841ca0ee3397e9a@AcuMS.aculab.com>
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On 12/29/23 15:56, David Laight wrote:
> osq_wait_next() is passed 'prev' from osq_lock() and NULL from osq_unlock()
> but only needs the 'cpu' value to write to lock->tail.
> Just pass prev->cpu or OSQ_UNLOCKED_VAL instead.
>
> Also directly return NULL or 'next' instead of breaking the loop.
>
> Should have no effect on the generated code since gcc manages to
> assume that 'prev != NULL' due to an earlier dereference.
>
> Signed-off-by: David Laight <david.laight@aculab.com>
> ---
>   kernel/locking/osq_lock.c | 23 ++++++++++-------------
>   1 file changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
> index 55f5db896c02..9bb3a077ba92 100644
> --- a/kernel/locking/osq_lock.c
> +++ b/kernel/locking/osq_lock.c
> @@ -48,18 +48,17 @@ static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
>   static inline struct optimistic_spin_node *
>   osq_wait_next(struct optimistic_spin_queue *lock,
>   	      struct optimistic_spin_node *node,
> -	      struct optimistic_spin_node *prev)
> +	      int old)

Make the last argument name more descriptive, like "old_cpu" as the 
"int" type does not provide enough context to allow people to guess what 
"old" may be.

Cheers,
Longman