From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759392Ab2EVRRt (ORCPT ); Tue, 22 May 2012 13:17:49 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:46896 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753288Ab2EVRRr (ORCPT ); Tue, 22 May 2012 13:17:47 -0400 Date: Tue, 22 May 2012 10:16:58 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: LKML , linaro-sched-sig@lists.linaro.org, Alessio Igor Bogani , Andrew Morton , Avi Kivity , Chris Metcalf , Christoph Lameter , Daniel Lezcano , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Ingo Molnar , Kevin Hilman , Max Krasnyansky , Peter Zijlstra , Stephen Hemminger , Steven Rostedt , Sven-Thorsten Dietrich , Thomas Gleixner Subject: Re: [PATCH 11/41] nohz/cpuset: Don't turn off the tick if rcu needs it Message-ID: <20120522171658.GA8087@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1335830115-14335-1-git-send-email-fweisbec@gmail.com> <1335830115-14335-12-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1335830115-14335-12-git-send-email-fweisbec@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12052217-5518-0000-0000-0000049757D7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 01, 2012 at 01:54:45AM +0200, Frederic Weisbecker wrote: > If RCU is waiting for the current CPU to complete a grace > period, don't turn off the tick. Unlike dynctik-idle, we > are not necessarily going to enter into rcu extended quiescent > state, so we may need to keep the tick to note current CPU's > quiescent states. > > [added build fix from Zen Lin] Hello, Frederic, One question below -- why not rcu_needs_cpu() instead of rcu_pending()? Thanx, Paul > Signed-off-by: Frederic Weisbecker > Cc: Alessio Igor Bogani > Cc: Andrew Morton > Cc: Avi Kivity > Cc: Chris Metcalf > Cc: Christoph Lameter > Cc: Daniel Lezcano > Cc: Geoff Levand > Cc: Gilad Ben Yossef > Cc: Hakan Akkan > Cc: Ingo Molnar > Cc: Kevin Hilman > Cc: Max Krasnyansky > Cc: Paul E. McKenney > Cc: Peter Zijlstra > Cc: Stephen Hemminger > Cc: Steven Rostedt > Cc: Sven-Thorsten Dietrich > Cc: Thomas Gleixner > --- > include/linux/rcupdate.h | 1 + > kernel/rcutree.c | 3 +-- > kernel/time/tick-sched.c | 22 ++++++++++++++++++---- > 3 files changed, 20 insertions(+), 6 deletions(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 81c04f4..e06639e 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -184,6 +184,7 @@ static inline int rcu_preempt_depth(void) > extern void rcu_sched_qs(int cpu); > extern void rcu_bh_qs(int cpu); > extern void rcu_check_callbacks(int cpu, int user); > +extern int rcu_pending(int cpu); > struct notifier_block; > extern void rcu_idle_enter(void); > extern void rcu_idle_exit(void); > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index 6c4a672..e141c7e 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -212,7 +212,6 @@ int rcu_cpu_stall_suppress __read_mostly; > module_param(rcu_cpu_stall_suppress, int, 0644); > > static void force_quiescent_state(struct rcu_state *rsp, int relaxed); > -static int rcu_pending(int cpu); > > /* > * Return the number of RCU-sched batches processed thus far for debug & stats. > @@ -1915,7 +1914,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) > * by the current CPU, returning 1 if so. This function is part of the > * RCU implementation; it is -not- an exported member of the RCU API. > */ > -static int rcu_pending(int cpu) > +int rcu_pending(int cpu) > { > return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) || > __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) || > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 43fa7ac..4f99766 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -506,9 +506,21 @@ void tick_nohz_idle_enter(void) > local_irq_enable(); > } > > +#ifdef CONFIG_CPUSETS_NO_HZ > +static bool can_stop_adaptive_tick(void) > +{ > + if (!sched_can_stop_tick()) > + return false; > + > + /* Is there a grace period to complete ? */ > + if (rcu_pending(smp_processor_id())) You lost me on this one. Why can't this be rcu_needs_cpu()? > + return false; > + > + return true; > +} > + > static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts) > { > -#ifdef CONFIG_CPUSETS_NO_HZ > int cpu = smp_processor_id(); > > if (!cpuset_adaptive_nohz() || is_idle_task(current)) > @@ -517,12 +529,14 @@ static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts) > if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) > return; > > - if (!sched_can_stop_tick()) > + if (!can_stop_adaptive_tick()) > return; > > tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); > -#endif > } > +#else > +static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts) { } > +#endif > > /** > * tick_nohz_irq_exit - update next tick event from interrupt exit > @@ -852,7 +866,7 @@ void tick_nohz_check_adaptive(void) > struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); > > if (ts->tick_stopped && !is_idle_task(current)) { > - if (!sched_can_stop_tick()) > + if (!can_stop_adaptive_tick()) > tick_nohz_restart_sched_tick(); > } > } > -- > 1.7.5.4 >