linux-kernel - Re: [PATCH tip/core/rcu 6/7] rcu: Move early-boot callbacks to no-CBs lists for no-CBs CPUs

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Date:	Tue, 3 Mar 2015 09:12:32 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com,
	bobby prani <bobby.prani@...il.com>
Subject: Re: [PATCH tip/core/rcu 6/7] rcu: Move early-boot callbacks to
 no-CBs lists for no-CBs CPUs

On Tue, Mar 03, 2015 at 04:57:16PM +0000, Mathieu Desnoyers wrote:
> ----- Original Message -----
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > To: linux-kernel@...r.kernel.org
> > Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, "mathieu desnoyers"
> > <mathieu.desnoyers@...icios.com>, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
> > rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
> > oleg@...hat.com, "bobby prani" <bobby.prani@...il.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > Sent: Tuesday, March 3, 2015 11:45:47 AM
> > Subject: [PATCH tip/core/rcu 6/7] rcu: Move early-boot callbacks to no-CBs lists for no-CBs CPUs
> > 
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > 
> > When a CPU is first determined to be a no-CBs CPUs, this commit causes
> > any early boot callbacks to be moved to the no-CBs callback list,
> > allowing them t obe invoked.
>                 ^^^^^
> out-of-order space ;)

I clearly needed a typography barrier!  ;-)

Good catch!

							Thanx, Paul

> Thanks,
> 
> Mathieu
> 
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  kernel/rcu/tree.c        |  1 +
> >  kernel/rcu/tree_plugin.h | 24 ++++++++++++------------
> >  2 files changed, 13 insertions(+), 12 deletions(-)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 92fd3eab5823..0317bf7d997f 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -2851,6 +2851,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct
> > rcu_head *rcu),
> >  		 * and then drop through to queue the callback.
> >  		 */
> >  		BUG_ON(cpu != -1);
> > +		WARN_ON_ONCE(!rcu_is_watching());
> >  		if (!likely(rdp->nxtlist))
> >  			init_default_callback_list(rdp);
> >  	}
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > index 75d5f096bcb0..afddd5641bea 100644
> > --- a/kernel/rcu/tree_plugin.h
> > +++ b/kernel/rcu/tree_plugin.h
> > @@ -2393,18 +2393,8 @@ void __init rcu_init_nohz(void)
> >  		pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
> >  
> >  	for_each_rcu_flavor(rsp) {
> > -		for_each_cpu(cpu, rcu_nocb_mask) {
> > -			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
> > -
> > -			/*
> > -			 * If there are early callbacks, they will need
> > -			 * to be moved to the nocb lists.
> > -			 */
> > -			WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
> > -				     &rdp->nxtlist &&
> > -				     rdp->nxttail[RCU_NEXT_TAIL] != NULL);
> > -			init_nocb_callback_list(rdp);
> > -		}
> > +		for_each_cpu(cpu, rcu_nocb_mask)
> > +			init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
> >  		rcu_organize_nocb_kthreads(rsp);
> >  	}
> >  }
> > @@ -2541,6 +2531,16 @@ static bool init_nocb_callback_list(struct rcu_data
> > *rdp)
> >  	if (!rcu_is_nocb_cpu(rdp->cpu))
> >  		return false;
> >  
> > +	/* If there are early-boot callbacks, move them to nocb lists. */
> > +	if (rdp->nxtlist) {
> > +		rdp->nocb_head = rdp->nxtlist;
> > +		rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
> > +		atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
> > +		atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
> > +		rdp->nxtlist = NULL;
> > +		rdp->qlen = 0;
> > +		rdp->qlen_lazy = 0;
> > +	}
> >  	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
> >  	return true;
> >  }
> > --
> > 1.8.1.5
> > 
> > 
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
> 

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