linux-kernel - Re: [PATCH v5 2/4] rcu: Reduce synchronize

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Message-ID: <Zd4V52g0ARybAUQE@localhost.localdomain>
Date: Tue, 27 Feb 2024 18:03:35 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>, RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v5 2/4] rcu: Reduce synchronize_rcu() latency

Le Tue, Feb 20, 2024 at 07:31:13PM +0100, Uladzislau Rezki (Sony) a écrit :
> +/*
> + * Helper function for rcu_gp_cleanup().
> + */
> +static void rcu_sr_normal_gp_cleanup(void)
> +{
> +	struct llist_node *wait_tail;
> +
> +	wait_tail = rcu_state.srs_wait_tail;
> +	if (wait_tail == NULL)
> +		return;
> +
> +	rcu_state.srs_wait_tail = NULL;
> +	ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail);
> +
> +	// concurrent sr_normal_gp_cleanup work might observe this update.
> +	smp_store_release(&rcu_state.srs_done_tail, wait_tail);
> +	ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail);
> +
> +	if (wait_tail)
> +		queue_work(system_highpri_wq, &rcu_state.srs_cleanup_work);

You can queue unconditionally here, wait_tail is non-NULL at this point.

Thanks.