linux-kernel - Re: [PATCH v2] rcu: Make call_rcu() lazy only when CONFIG_RCU

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Date:   Wed, 19 Oct 2022 16:52:57 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     frederic@...nel.org, joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rcu: Make call_rcu() lazy only when CONFIG_RCU_LAZY
 is enabled

On Thu, Oct 20, 2022 at 07:38:35AM +0800, Zqiang wrote:
> Currently, regardless of whether the CONFIG_RCU_LAZY is enabled,
> invoke the call_rcu() is always lazy, it also means that when
> CONFIG_RCU_LAZY is disabled, invoke the call_rcu_flush() is also
> lazy. therefore, this commit make call_rcu() lazy only when
> CONFIG_RCU_LAZY is enabled.
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> ---
>  v1->v2: 
>  Use IS_ENABLED(CONFIG_RCU_LAZY) to the existing function of the same name.
> 
>  kernel/rcu/tree.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index abc615808b6e..ecf42b0d3726 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2887,7 +2887,10 @@ EXPORT_SYMBOL_GPL(call_rcu_flush);
>   */
>  void call_rcu(struct rcu_head *head, rcu_callback_t func)
>  {
> -	return __call_rcu_common(head, func, true);
> +	if (IS_ENABLED(CONFIG_RCU_LAZY))
> +		return __call_rcu_common(head, func, true);
> +	else
> +		return __call_rcu_common(head, func, false);

This is much better, but why not something like this?

	return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));

							Thanx, Paul

>  }
>  EXPORT_SYMBOL_GPL(call_rcu);
>  
> -- 
> 2.25.1
>