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From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org
Subject: Re: need_heavy_qs flag for PREEMPT=y kernels
Date: Mon, 12 Aug 2019 19:28:29 -0700
Message-ID: <20190813022829.GX28441@linux.ibm.com> (raw)
In-Reply-To: <20190813010525.GB129011@google.com>

On Mon, Aug 12, 2019 at 09:05:25PM -0400, Joel Fernandes wrote:
> On Mon, Aug 12, 2019 at 09:02:49PM -0400, Joel Fernandes wrote:
> [snip]
> > > 							Thanx, Paul
> > > 
> > > ------------------------------------------------------------------------
> > > 
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 8c494a692728..ad906d6a74fb 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -651,6 +651,12 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
> > >  	 */
> > >  	if (rdp->dynticks_nmi_nesting != 1) {
> > >  		trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
> > > +		if (tick_nohz_full_cpu(rdp->cpu) &&
> > > +		    rdp->dynticks_nmi_nesting == 2 &&
> > > +		    rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
> > > +			rdp->rcu_forced_tick = true;
> > > +			tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU);
> > > +		}
> > 
> > 
> > Instead of checking dynticks_nmi_nesting == 2 in rcu_nmi_exit_common(), can
> > we do the tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU)  from
> > rcu_nmi_enter_common() ? We could add this code there, under the "if
> > (rcu_dynticks_curr_cpu_in_eqs())".
> 
> Actually, the other way. if (!rcu_dynticks_curr_cpu_in_eqs()) then do the
> tick_dep_set_cpu().

That does sound more likely.  Still, need to work out what the
breakage is.

							Thanx, Paul


  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-11 18:08 Joel Fernandes
2019-08-11 18:34 ` Joel Fernandes
2019-08-11 21:16   ` Paul E. McKenney
2019-08-11 21:25     ` Joel Fernandes
2019-08-11 23:30       ` Paul E. McKenney
2019-08-12  1:24         ` Joel Fernandes
2019-08-12  1:40           ` Joel Fernandes
2019-08-12  3:57             ` Paul E. McKenney
2019-08-11 21:13 ` Paul E. McKenney
2019-08-12  3:21   ` Joel Fernandes
2019-08-12  3:53     ` Paul E. McKenney
2019-08-12 21:20       ` Joel Fernandes
2019-08-12 23:01         ` Paul E. McKenney
2019-08-13  1:02           ` Joel Fernandes
2019-08-13  1:05             ` Joel Fernandes
2019-08-13  2:28               ` Paul E. McKenney [this message]
2019-08-13  2:27             ` Paul E. McKenney
2019-08-13  2:50               ` Paul E. McKenney
2019-08-15 17:17             ` Paul E. McKenney
2019-08-15 20:04               ` Joel Fernandes
2019-08-15 20:31                 ` Paul E. McKenney
2019-08-15 21:22                   ` Joel Fernandes
2019-08-15 21:27                     ` Joel Fernandes
2019-08-15 21:34                       ` Joel Fernandes
2019-08-15 21:57                         ` Paul E. McKenney
2019-08-15 21:45                     ` Paul E. McKenney
2019-08-16  0:02                       ` Joel Fernandes
2019-08-19 12:34                         ` Frederic Weisbecker
2019-08-19 12:09                   ` Frederic Weisbecker
2019-08-19 16:57                   ` Frederic Weisbecker
2019-08-19 22:31                     ` Paul E. McKenney

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