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

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Date:   Tue, 16 Mar 2021 07:02:00 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...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 Tue, Mar 16, 2021 at 12:45:26PM +0100, Frederic Weisbecker wrote:
> 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.

And with this, light rcutorture testing passed.  I hope to pound on it
harder later this week.

							Thanx, Paul