From: Joel Fernandes <joel@joelfernandes.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, elver@google.com,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
rcu@vger.kernel.org
Subject: Re: [PATCH] rcu: Avoid to modify mask_ofl_ipi in sync_rcu_exp_select_node_cpus()
Date: Tue, 8 Oct 2019 12:30:28 -0400 [thread overview]
Message-ID: <20191008163028.GA136151@google.com> (raw)
In-Reply-To: <20191008050145.4041702-1-boqun.feng@gmail.com>
On Tue, Oct 08, 2019 at 01:01:40PM +0800, Boqun Feng wrote:
> "mask_ofl_ipi" is used for iterate CPUs which IPIs are needed to send
> to, however in the IPI sending loop, "mask_ofl_ipi" along with another
> variable "mask_ofl_test" might also get modified to record which CPU's
> quiesent state can be reported by sync_rcu_exp_select_node_cpus(). Two
> variables seems to be redundant for such a propose, so this patch clean
> things a little by solely using "mask_ofl_test" for recording and
> "mask_ofl_ipi" for iteration. This would improve the readibility of the
> IPI sending loop in sync_rcu_exp_select_node_cpus().
>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
thanks,
- Joel
> kernel/rcu/tree_exp.h | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index 69c5aa64fcfd..212470018752 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -387,10 +387,10 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
> }
> ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
> put_cpu();
> - if (!ret) {
> - mask_ofl_ipi &= ~mask;
> + /* The CPU responses the IPI, and will report QS itself */
> + if (!ret)
> continue;
> - }
> +
> /* Failed, raced with CPU hotplug operation. */
> raw_spin_lock_irqsave_rcu_node(rnp, flags);
> if ((rnp->qsmaskinitnext & mask) &&
> @@ -401,13 +401,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
> schedule_timeout_uninterruptible(1);
> goto retry_ipi;
> }
> - /* CPU really is offline, so we can ignore it. */
> - if (!(rnp->expmask & mask))
> - mask_ofl_ipi &= ~mask;
> + /* CPU really is offline, and we need its QS to pass GP. */
> + if (rnp->expmask & mask)
> + mask_ofl_test |= mask;
> raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> }
> /* Report quiescent states for those that went offline. */
> - mask_ofl_test |= mask_ofl_ipi;
> if (mask_ofl_test)
> rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
> }
> --
> 2.23.0
>
next prev parent reply other threads:[~2019-10-08 16:30 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 5:01 [PATCH] rcu: Avoid to modify mask_ofl_ipi in sync_rcu_exp_select_node_cpus() Boqun Feng
2019-10-08 13:12 ` Paul E. McKenney
2019-10-08 16:30 ` Joel Fernandes [this message]
2019-10-08 16:35 ` Marco Elver
2019-10-08 17:01 ` Joel Fernandes
2019-10-09 2:20 ` Boqun Feng
2019-10-09 14:25 ` Joel Fernandes
2019-10-09 15:45 ` Paul E. McKenney
2019-10-09 15:44 ` Paul E. McKenney
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