From: Frederic Weisbecker <frederic@kernel.org>
To: paulmck@kernel.org
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org
Subject: Re: [PATCH tip/core/rcu 1/3] rcu: Provide polling interfaces for Tree RCU grace periods
Date: Tue, 16 Mar 2021 15:47:22 +0100 [thread overview]
Message-ID: <20210316144722.GD639918@lothringen> (raw)
In-Reply-To: <20210304002632.23870-1-paulmck@kernel.org>
On Wed, Mar 03, 2021 at 04:26:30PM -0800, paulmck@kernel.org wrote:
> +/**
> + * poll_state_synchronize_rcu - Conditionally wait for an RCU grace period
> + *
> + * @oldstate: return from call to get_state_synchronize_rcu() or start_poll_synchronize_rcu()
> + *
> + * If a full RCU grace period has elapsed since the earlier call from
> + * which oldstate was obtained, return @true, otherwise return @false.
> + * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
> + *
> + * Yes, this function does not take counter wrap into account.
> + * But counter wrap is harmless. If the counter wraps, we have waited for
> + * more than 2 billion grace periods (and way more on a 64-bit system!).
> + * Those needing to keep oldstate values for very long time periods
> + * (many hours even on 32-bit systems) should check them occasionally
> + * and either refresh them or set a flag indicating that the grace period
> + * has completed.
> + */
> +bool poll_state_synchronize_rcu(unsigned long oldstate)
> +{
> + if (rcu_seq_done(&rcu_state.gp_seq, oldstate)) {
> + smp_mb(); /* Ensure GP ends before subsequent accesses. */
> + return true;
> + }
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
> +
> +/**
> * cond_synchronize_rcu - Conditionally wait for an RCU grace period
> *
> * @oldstate: return value from earlier call to get_state_synchronize_rcu()
> *
> * If a full RCU grace period has elapsed since the earlier call to
> - * get_state_synchronize_rcu(), just return. Otherwise, invoke
> - * synchronize_rcu() to wait for a full grace period.
> + * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
> + * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
> *
> * Yes, this function does not take counter wrap into account. But
> * counter wrap is harmless. If the counter wraps, we have waited for
> @@ -3804,7 +3864,7 @@ EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
> */
> void cond_synchronize_rcu(unsigned long oldstate)
> {
> - if (!rcu_seq_done(&rcu_state.gp_seq, oldstate))
> + if (!poll_state_synchronize_rcu(oldstate))
> synchronize_rcu();
> else
> smp_mb(); /* Ensure GP ends before subsequent accesses. */
poll_state_synchronize_rcu() already does the full barrier.
> --
> 2.9.5
>
next prev parent reply other threads:[~2021-03-16 14:48 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 0:26 [PATCH tip/core/rcu 0/3] Polling RCU grace-period interfaces for v5.13 Paul E. McKenney
2021-03-04 0:26 ` [PATCH tip/core/rcu 1/3] rcu: Provide polling interfaces for Tree RCU grace periods paulmck
2021-03-12 12:21 ` Frederic Weisbecker
2021-03-12 12:26 ` Frederic Weisbecker
2021-03-15 23:11 ` Paul E. McKenney
2021-03-16 14:47 ` Frederic Weisbecker [this message]
2021-03-16 16:42 ` Paul E. McKenney
2021-03-16 15:17 ` Frederic Weisbecker
2021-03-16 16:51 ` Paul E. McKenney
2021-03-18 14:59 ` Frederic Weisbecker
2021-03-18 17:09 ` Paul E. McKenney
2021-03-19 13:58 ` Frederic Weisbecker
2021-03-19 17:51 ` Paul E. McKenney
2021-03-19 22:10 ` Frederic Weisbecker
2021-03-19 23:38 ` Paul E. McKenney
2021-03-19 23:47 ` Frederic Weisbecker
2021-03-04 0:26 ` [PATCH tip/core/rcu 2/3] rcu: Provide polling interfaces for Tiny " paulmck
2021-03-21 22:28 ` Frederic Weisbecker
2021-03-22 15:47 ` Paul E. McKenney
2021-03-22 19:00 ` Frederic Weisbecker
2021-03-22 19:45 ` Paul E. McKenney
2021-03-23 14:02 ` Frederic Weisbecker
2021-03-23 16:45 ` Paul E. McKenney
2021-03-04 0:26 ` [PATCH tip/core/rcu 3/3] rcutorture: Test start_poll_synchronize_rcu() and poll_state_synchronize_rcu() paulmck
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