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

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Message-ID: <PH0PR11MB58809A4318B47FA8669C4360DA2A9@PH0PR11MB5880.namprd11.prod.outlook.com>
Date:   Thu, 20 Oct 2022 00:49:56 +0000
From:   "Zhang, Qiang1" <qiang1.zhang@...el.com>
To:     "paulmck@...nel.org" <paulmck@...nel.org>
CC:     "frederic@...nel.org" <frederic@...nel.org>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "linux-kernel@...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?

Yes, it looks better, 😊.

>
>	return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
>
>							Thanx, Paul

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