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From:   Joel Fernandes <joel@joelfernandes.org>
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Subject: Re: [PATCH] rcu: Make call_rcu() lazy only when CONFIG_RCU_LAZY is enabled
Date:   Wed, 19 Oct 2022 08:10:48 -0400
Message-Id: <B3E5FB1F-3184-4C56-8B11-6F422DBF1B53@joelfernandes.org>
References: <20221019104045.160283-1-qiang1.zhang@intel.com>
Cc:     paulmck@kernel.org, frederic@kernel.org, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <20221019104045.160283-1-qiang1.zhang@intel.com>
To:     Zqiang <qiang1.zhang@intel.com>
Precedence: bulk


> On Oct 19, 2022, at 6:34 AM, Zqiang <qiang1.zhang@intel.com> wrote:
>=20
> =EF=BB=BFCurrently, 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.
>=20
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> ---
> kernel/rcu/tree.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>=20
> 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_callb=
ack_t func)
>    return __call_rcu_common(head, func, false);
> }
> EXPORT_SYMBOL_GPL(call_rcu_flush);
> -#endif
>=20
> /**
>  * 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=E2=
=80=A6) to the existing function of the same name.

Looks like though I made every one test the patch without having to enable t=
he config option ;-). Hey, I=E2=80=99m a half glass full kind of guy, why do=
 you ask?

Paul, I=E2=80=99ll take a closer look once I=E2=80=99m at the desk, but woul=
d you prefer to squash a diff into the existing patch, or want a new patch a=
ltogether?

Thanks.

- Joel


> +}
> +EXPORT_SYMBOL_GPL(call_rcu);
> +#endif
>=20
> /* Maximum number of jiffies to wait before draining a batch. */
> #define KFREE_DRAIN_JIFFIES (5 * HZ)
> --=20
> 2.25.1
>=20