Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:6 as permitted sender) client-ip=2620:137:e000::3:6;
Message-ID: <535dd61c-8e3e-103c-e970-2c8514af5596@redhat.com>
Date:   Tue, 10 Oct 2023 19:07:05 -0400
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.14.0
Subject: Re: [PATCH] locking/osq: remove spin node definition from header
Content-Language: en-US
To:     =?UTF-8?Q?Thomas_Wei=c3=9fschuh?= <linux@weissschuh.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>
Cc:     linux-kernel@vger.kernel.org
References: <20231010-osq-header-v1-1-d68fbc1bf1cf@weissschuh.net>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20231010-osq-header-v1-1-d68fbc1bf1cf@weissschuh.net>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 10/10/23 05:53, Thomas Weißschuh wrote:
> This structure is an implementation detail of osq_lock.c, and there are
> no external users.
>
> Also drop the redundant overview comment from osq_lock.c.
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>   include/linux/osq_lock.h  | 5 -----
>   kernel/locking/osq_lock.c | 9 ++++++---
>   2 files changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/osq_lock.h b/include/linux/osq_lock.h
> index 5581dbd3bd34..ea8fb31379e3 100644
> --- a/include/linux/osq_lock.h
> +++ b/include/linux/osq_lock.h
> @@ -6,11 +6,6 @@
>    * An MCS like lock especially tailored for optimistic spinning for sleeping
>    * lock implementations (mutex, rwsem, etc).
>    */
> -struct optimistic_spin_node {
> -	struct optimistic_spin_node *next, *prev;
> -	int locked; /* 1 if lock acquired */
> -	int cpu; /* encoded CPU # + 1 value */
> -};

It is probably better to drop the MCS like lock comment here as it is 
not relevant without the optimistic_spin_node struct.


>   
>   struct optimistic_spin_queue {
>   	/*
> diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
> index d5610ad52b92..918866edbc30 100644
> --- a/kernel/locking/osq_lock.c
> +++ b/kernel/locking/osq_lock.c
> @@ -3,10 +3,13 @@
>   #include <linux/sched.h>
>   #include <linux/osq_lock.h>
>   
> +struct optimistic_spin_node {
> +	struct optimistic_spin_node *next, *prev;
> +	int locked; /* 1 if lock acquired */
> +	int cpu; /* encoded CPU # + 1 value */
> +};
> +
>   /*
> - * An MCS like lock especially tailored for optimistic spinning for sleeping
> - * lock implementations (mutex, rwsem, etc).
> - *
>    * Using a single mcs node per CPU is safe because sleeping locks should not be
>    * called from interrupt context and we have preemption disabled while
>    * spinning.

We should keep the MCS comment here. My other suggestion is to put the 
structure definition after the comment.

Other than these minor nits, it is a worthwhile cleanup patch.

Cheers,
Longman