linux-kernel - Re: [PATCH 12/13] rcu/nocb: Prepare for finegrained deferred wakeup

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Message-ID: <20210316114526.GA639918@lothringen>
Date:   Tue, 16 Mar 2021 12:45:26 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Stable <stable@...r.kernel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 12/13] rcu/nocb: Prepare for finegrained deferred wakeup

On Mon, Mar 15, 2021 at 08:02:39PM -0700, Paul E. McKenney wrote:
> On Tue, Feb 23, 2021 at 01:10:10AM +0100, Frederic Weisbecker wrote:
> > Provide a way to tune the deferred wakeup level we want to perform from
> > a safe wakeup point. Currently those sites are:
> > 
> > * nocb_timer
> > * user/idle/guest entry
> > * CPU down
> > * softirq/rcuc
> > 
> > All of these sites perform the wake up for both RCU_NOCB_WAKE and
> > RCU_NOCB_WAKE_FORCE.
> > 
> > In order to merge nocb_timer and nocb_bypass_timer together, we plan to
> > add a new RCU_NOCB_WAKE_BYPASS that really want to be deferred until
> > a timer fires so that we don't wake up the NOCB-gp kthread too early.
> > 
> > To prepare for that, integrate a wake up level/limit that a callsite is
> > deemed to perform.
> 
> This appears to need the following in order to build for non-NOCB
> configurations.  I will fold it in and am retesting.
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 55f59dd75a11455cf558fd387fbf9011017dcc8a
> Author: Paul E. McKenney <paulmck@...nel.org>
> Date:   Mon Mar 15 20:00:34 2021 -0700
> 
>     squash! rcu/nocb: Prepare for fine-grained deferred wakeup
>     
>     [ paulmck: Fix non-NOCB rcu_nocb_need_deferred_wakeup() definition. ]
>     Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 0cc7f68..dfb048e 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2926,7 +2926,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
>  {
>  }
>  
> -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
> +static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
>  {
>  	return false;
>  }


Oops thanks, I missed that.