From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755015Ab2IBBXE (ORCPT ); Sat, 1 Sep 2012 21:23:04 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:60792 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751821Ab2IBBXB (ORCPT ); Sat, 1 Sep 2012 21:23:01 -0400 X-Originating-IP: 217.70.178.130 X-Originating-IP: 50.43.46.74 Date: Sat, 1 Sep 2012 18:22:53 -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 03/23] rcu: Move RCU grace-period cleanup into kthread Message-ID: <20120902012252.GC5713@leaf> References: <20120830181811.GA29154@linux.vnet.ibm.com> <1346350718-30937-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346350718-30937-3-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: <1346350718-30937-3-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 11:18:18AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > As a first step towards allowing grace-period cleanup to be preemptible, > this commit moves the RCU grace-period cleanup into the same kthread > that is now used to initialize grace periods. This is needed to keep > scheduling latency down to a dull roar. > > Reported-by: Mike Galbraith > Reported-by: Dimitri Sivanich > Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett > kernel/rcutree.c | 112 ++++++++++++++++++++++++++++++------------------------ > 1 files changed, 62 insertions(+), 50 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index ef56aa3..9fad21c 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1045,6 +1045,7 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat > static int rcu_gp_kthread(void *arg) > { > unsigned long flags; > + unsigned long gp_duration; > struct rcu_data *rdp; > struct rcu_node *rnp; > struct rcu_state *rsp = arg; > @@ -1135,6 +1136,65 @@ static int rcu_gp_kthread(void *arg) > rsp->fqs_state = RCU_SIGNAL_INIT; > raw_spin_unlock_irqrestore(&rnp->lock, flags); > put_online_cpus(); > + > + /* Handle grace-period end. */ > + rnp = rcu_get_root(rsp); > + for (;;) { > + wait_event_interruptible(rsp->gp_wq, > + !ACCESS_ONCE(rnp->qsmask) && > + !rcu_preempt_blocked_readers_cgp(rnp)); > + if (!ACCESS_ONCE(rnp->qsmask) && > + !rcu_preempt_blocked_readers_cgp(rnp)) > + break; > + flush_signals(current); > + } > + > + raw_spin_lock_irqsave(&rnp->lock, flags); > + gp_duration = jiffies - rsp->gp_start; > + if (gp_duration > rsp->gp_max) > + rsp->gp_max = gp_duration; > + > + /* > + * We know the grace period is complete, but to everyone else > + * it appears to still be ongoing. But it is also the case > + * that to everyone else it looks like there is nothing that > + * they can do to advance the grace period. It is therefore > + * safe for us to drop the lock in order to mark the grace > + * period as completed in all of the rcu_node structures. > + * > + * But if this CPU needs another grace period, it will take > + * care of this while initializing the next grace period. > + * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL > + * because the callbacks have not yet been advanced: Those > + * callbacks are waiting on the grace period that just now > + * completed. > + */ > + if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { > + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > + > + /* > + * Propagate new ->completed value to rcu_node > + * structures so that other CPUs don't have to > + * wait until the start of the next grace period > + * to process their callbacks. > + */ > + rcu_for_each_node_breadth_first(rsp, rnp) { > + /* irqs already disabled. */ > + raw_spin_lock(&rnp->lock); > + rnp->completed = rsp->gpnum; > + /* irqs remain disabled. */ > + raw_spin_unlock(&rnp->lock); > + } > + rnp = rcu_get_root(rsp); > + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > + } > + > + rsp->completed = rsp->gpnum; /* Declare grace period done. */ > + trace_rcu_grace_period(rsp->name, rsp->completed, "end"); > + rsp->fqs_state = RCU_GP_IDLE; > + if (cpu_needs_another_gp(rsp, rdp)) > + rsp->gp_flags = 1; > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > } > return 0; > } > @@ -1182,57 +1242,9 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) > static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) > __releases(rcu_get_root(rsp)->lock) > { > - unsigned long gp_duration; > - struct rcu_node *rnp = rcu_get_root(rsp); > - struct rcu_data *rdp = this_cpu_ptr(rsp->rda); > - > WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); > - > - /* > - * Ensure that all grace-period and pre-grace-period activity > - * is seen before the assignment to rsp->completed. > - */ > - smp_mb(); /* See above block comment. */ > - gp_duration = jiffies - rsp->gp_start; > - if (gp_duration > rsp->gp_max) > - rsp->gp_max = gp_duration; > - > - /* > - * We know the grace period is complete, but to everyone else > - * it appears to still be ongoing. But it is also the case > - * that to everyone else it looks like there is nothing that > - * they can do to advance the grace period. It is therefore > - * safe for us to drop the lock in order to mark the grace > - * period as completed in all of the rcu_node structures. > - * > - * But if this CPU needs another grace period, it will take > - * care of this while initializing the next grace period. > - * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL > - * because the callbacks have not yet been advanced: Those > - * callbacks are waiting on the grace period that just now > - * completed. > - */ > - if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > - > - /* > - * Propagate new ->completed value to rcu_node structures > - * so that other CPUs don't have to wait until the start > - * of the next grace period to process their callbacks. > - */ > - rcu_for_each_node_breadth_first(rsp, rnp) { > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > - rnp->completed = rsp->gpnum; > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > - } > - rnp = rcu_get_root(rsp); > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > - } > - > - rsp->completed = rsp->gpnum; /* Declare the grace period complete. */ > - trace_rcu_grace_period(rsp->name, rsp->completed, "end"); > - rsp->fqs_state = RCU_GP_IDLE; > - rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ > + raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); > + wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ > } > > /* > -- > 1.7.8 >