linux-kernel - Re: [PATCH 3/3] rcu/exp: Remove needless CPU up quiescent state report

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Message-ID: <Z7icO5sp9SoXZSJs@localhost.localdomain>
Date: Fri, 21 Feb 2025 16:31:07 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, rcu <rcu@...r.kernel.org>
Subject: Re: [PATCH 3/3] rcu/exp: Remove needless CPU up quiescent state
 report

Le Wed, Feb 19, 2025 at 07:55:05AM -0800, Paul E. McKenney a écrit :
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 86935fe00397..40d6090a33f5 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -4347,6 +4347,12 @@ void rcutree_report_cpu_dead(void)
> > >  	 * may introduce a new READ-side while it is actually off the QS masks.
> > >  	 */
> > >  	lockdep_assert_irqs_disabled();
> > > +	/*
> > > +	 * CPUHP_AP_SMPCFD_DYING was the last call for rcu_exp_handler() execution.
> > > +	 * The requested QS must have been reported on the last context switch
> > > +	 * from stop machine to idle.
> > > +	 */
> > > +	WARN_ON_ONCE(rdp->cpu_no_qs.b.exp);
> > >  	// Do any dangling deferred wakeups.
> > >  	do_nocb_deferred_wakeup(rdp);
> > 
> > I fired off a 30-minute run of 100*TREE03 with this change also.
> 
> And no failures!

Ok I'm adding that one on my queue.

> 
> 							Thanx, Paul
> 
> > > > 3.	Your ideas here!  ;-)
> > > 
> > > :-)
> > 
> > 							Thanx, Paul