From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755818Ab2IBBgk (ORCPT ); Sat, 1 Sep 2012 21:36:40 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:52826 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754181Ab2IBBgj (ORCPT ); Sat, 1 Sep 2012 21:36:39 -0400 X-Originating-IP: 217.70.178.138 X-Originating-IP: 50.43.46.74 Date: Sat, 1 Sep 2012 18:36:31 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 04/23] rcu: Allow RCU grace-period cleanup to be preempted Message-ID: <20120902013631.GD5713@leaf> References: <20120830181811.GA29154@linux.vnet.ibm.com> <1346350718-30937-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346350718-30937-4-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1346350718-30937-4-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 30, 2012 at 11:18:19AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > RCU grace-period cleanup is currently carried out with interrupts > disabled, which can result in excessive latency spikes on large systems > (many hundreds or thousands of CPUs). This patch therefore makes the > RCU grace-period cleanup be preemptible, including voluntary preemption > points, which should eliminate those latency spikes. Similar spikes from > forcing of quiescent states will be dealt with similarly by later patches. > > Reported-by: Mike Galbraith > Reported-by: Dimitri Sivanich > Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett > kernel/rcutree.c | 11 +++++------ > 1 files changed, 5 insertions(+), 6 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index 9fad21c..300aba6 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1170,7 +1170,7 @@ static int rcu_gp_kthread(void *arg) > * completed. > */ > if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > /* > * Propagate new ->completed value to rcu_node > @@ -1179,14 +1179,13 @@ static int rcu_gp_kthread(void *arg) > * to process their callbacks. > */ > rcu_for_each_node_breadth_first(rsp, rnp) { > - /* irqs already disabled. */ > - raw_spin_lock(&rnp->lock); > + raw_spin_lock_irqsave(&rnp->lock, flags); > rnp->completed = rsp->gpnum; > - /* irqs remain disabled. */ > - raw_spin_unlock(&rnp->lock); > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > + cond_resched(); > } > rnp = rcu_get_root(rsp); > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > + raw_spin_lock_irqsave(&rnp->lock, flags); > } > > rsp->completed = rsp->gpnum; /* Declare grace period done. */ > -- > 1.7.8 >