linux-kernel - Re: [PATCH RFC tip/core/rcu 5/5] rcu: Limit expedited helping to every 10 ms or every 4th GP

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Message-ID: <20150630221056.GP3717@linux.vnet.ibm.com>
Date:	Tue, 30 Jun 2015 15:10:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, laijs@...fujitsu.com,
	dipankar@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	Thomas Gleixner <tglx@...utronix.de>, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 5/5] rcu: Limit expedited helping to
 every 10 ms or every 4th GP

On Tue, Jun 30, 2015 at 11:56:37PM +0200, Eric Dumazet wrote:
> On Tue, Jun 30, 2015 at 11:48 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> >
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  kernel/rcu/tree.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 308b6acb4260..247aa1120c4c 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3505,10 +3505,19 @@ void synchronize_sched_expedited(void)
> >                            !atomic_read(&rsp->expedited_need_qs));
> >
> >         rcu_exp_gp_seq_end(rsp);
> > -       mutex_unlock(&rnp->exp_funnel_mutex);
> >         smp_mb(); /* ensure subsequent action seen after grace period. */
> > -       if (rsp->gp_kthread && rcu_gp_in_progress(rsp))
> > -               wake_up(&rsp->gp_wq);
> > +       if (rsp->gp_kthread && rcu_gp_in_progress(rsp)) {
> > +               static unsigned long nextgp;
> > +               static unsigned long nextjiffy;
> > +
> > +               if (time_after_eq(jiffies, nextgp) ||
> > +                   ULONG_CMP_GE(rsp->gpnum, nextgp)) {
> > +                       nextgp = rsp->gpnum + 4;
> > +                       nextjiffy = jiffies + 10;
> 
> Do you want 10 ticks or 10 ms (as stated in title) ?

Ten ticks, good catch!

							Thanx, Paul

> > +                       wake_up(&rsp->gp_wq);
> > +               }
> > +       }
> > +       mutex_unlock(&rnp->exp_funnel_mutex);
> >
> >         put_online_cpus();
> >  }
> > --
> > 1.8.1.5
> >
> 

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