From: "Paul E. McKenney" <paulmck@kernel.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Boqun Feng <boqun.feng@gmail.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Josh Triplett <josh@joshtriplett.org>,
Stable <stable@vger.kernel.org>,
Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH 11/13] rcu/nocb: Only cancel nocb timer if not polling
Date: Tue, 2 Mar 2021 17:22:29 -0800 [thread overview]
Message-ID: <20210303012229.GB20917@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20210223001011.127063-12-frederic@kernel.org>
On Tue, Feb 23, 2021 at 01:10:09AM +0100, Frederic Weisbecker wrote:
> No need to disarm the nocb_timer if rcu_nocb is polling because it
> shouldn't be armed either.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
> Cc: Boqun Feng <boqun.feng@gmail.com>
OK, so it does make sense to move that del_timer() under the following
"if" statement, then. ;-)
> ---
> kernel/rcu/tree_plugin.h | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 9da67b0d3997..d8b50ff40e4b 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2186,18 +2186,18 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
> my_rdp->nocb_gp_gp = needwait_gp;
> my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
> if (bypass) {
> - raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
> - // Avoid race with first bypass CB.
> - if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
> - WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
> - del_timer(&my_rdp->nocb_timer);
> - }
> if (!rcu_nocb_poll) {
> + raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
> + // Avoid race with first bypass CB.
> + if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
> + WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
> + del_timer(&my_rdp->nocb_timer);
> + }
> // At least one child with non-empty ->nocb_bypass, so set
> // timer in order to avoid stranding its callbacks.
> mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
> + raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
> }
> - raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
> }
> if (rcu_nocb_poll) {
> /* Polling, so trace if first poll in the series. */
> --
> 2.25.1
>
next prev parent reply other threads:[~2021-03-03 13:41 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 0:09 [PATCH 00/13] rcu/nocb updates v2 Frederic Weisbecker
2021-02-23 0:09 ` [PATCH 01/13] rcu/nocb: Fix potential missed nocb_timer rearm Frederic Weisbecker
2021-02-24 18:37 ` Paul E. McKenney
2021-02-24 22:06 ` Frederic Weisbecker
2021-02-25 0:14 ` Paul E. McKenney
2021-02-25 0:48 ` Frederic Weisbecker
2021-02-25 1:07 ` Paul E. McKenney
2021-03-02 1:48 ` Paul E. McKenney
2021-03-02 12:34 ` Frederic Weisbecker
2021-03-02 18:17 ` Paul E. McKenney
2021-03-03 1:35 ` Frederic Weisbecker
2021-03-03 2:06 ` Paul E. McKenney
2021-03-03 2:17 ` Frederic Weisbecker
2021-03-03 11:15 ` Neeraj Upadhyay
2021-02-23 0:10 ` [PATCH 02/13] rcu/nocb: Disable bypass when CPU isn't completely offloaded Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 03/13] rcu/nocb: Remove stale comment above rcu_segcblist_offload() Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 04/13] rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb_lock when possible Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 05/13] rcu/nocb: Merge nocb_timer to the rdp leader Frederic Weisbecker
2021-03-03 1:15 ` [PATCH 05/13] rcu/nocb: Use the rcuog CPU's ->nocb_timer Paul E. McKenney
2021-03-10 22:05 ` Frederic Weisbecker
2021-03-16 0:02 ` Paul E. McKenney
2021-02-23 0:10 ` [PATCH 06/13] timer: Revert "timer: Add timer_curr_running()" Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 07/13] rcu/nocb: Directly call __wake_nocb_gp() from bypass timer Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 08/13] rcu/nocb: Allow de-offloading rdp leader Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 09/13] rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 10/13] rcu/nocb: Delete bypass_timer " Frederic Weisbecker
2021-03-03 1:24 ` Paul E. McKenney
2021-03-10 22:17 ` Frederic Weisbecker
2021-03-15 14:53 ` Boqun Feng
2021-03-15 22:56 ` Frederic Weisbecker
2021-03-16 0:02 ` Paul E. McKenney
2021-02-23 0:10 ` [PATCH 11/13] rcu/nocb: Only cancel nocb timer if not polling Frederic Weisbecker
2021-03-03 1:22 ` Paul E. McKenney [this message]
2021-03-10 22:08 ` Frederic Weisbecker
2021-02-23 0:10 ` [PATCH 12/13] rcu/nocb: Prepare for finegrained deferred wakeup Frederic Weisbecker
2021-03-16 3:02 ` Paul E. McKenney
2021-03-16 11:45 ` Frederic Weisbecker
2021-03-16 14:02 ` Paul E. McKenney
2021-02-23 0:10 ` [PATCH 13/13] rcu/nocb: Unify timers Frederic Weisbecker
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