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

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Date:   Wed, 19 Oct 2022 08:10:48 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     paulmck@...nel.org, frederic@...nel.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: Make call_rcu() lazy only when CONFIG_RCU_LAZY is enabled



> On Oct 19, 2022, at 6:34 AM, Zqiang <qiang1.zhang@...el.com> 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>
> ---
> kernel/rcu/tree.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index abc615808b6e..97ef602da3d5 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2839,7 +2839,6 @@ void call_rcu_flush(struct rcu_head *head, rcu_callback_t func)
>    return __call_rcu_common(head, func, false);
> }
> EXPORT_SYMBOL_GPL(call_rcu_flush);
> -#endif
> 
> /**
>  * call_rcu() - Queue an RCU callback for invocation after a grace period.
> @@ -2890,6 +2889,13 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
>    return __call_rcu_common(head, func, true);
> }
> EXPORT_SYMBOL_GPL(call_rcu);
> +#else
> +void call_rcu(struct rcu_head *head, rcu_callback_t func)
> +{
> +    return __call_rcu_common(head, func, false);

Thanks. Instead of adding new function, you can also pass IS_ENABLED(CONFIG…) to the existing function of the same name.

Looks like though I made every one test the patch without having to enable the config option ;-). Hey, I’m a half glass full kind of guy, why do you ask?

Paul, I’ll take a closer look once I’m at the desk, but would you prefer to squash a diff into the existing patch, or want a new patch altogether?

Thanks.

- Joel


> +}
> +EXPORT_SYMBOL_GPL(call_rcu);
> +#endif
> 
> /* Maximum number of jiffies to wait before draining a batch. */
> #define KFREE_DRAIN_JIFFIES (5 * HZ)
> -- 
> 2.25.1
>