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

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Message-ID: <20210316030239.GA13675@paulmck-ThinkPad-P72>
Date:   Mon, 15 Mar 2021 20:02:39 -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, 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;
 }