Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753977Ab3J2Jvn (ORCPT ); Tue, 29 Oct 2013 05:51:43 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:60188 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753901Ab3J2Jvl (ORCPT ); Tue, 29 Oct 2013 05:51:41 -0400 Date: Tue, 29 Oct 2013 02:51:35 -0700 From: "Paul E. McKenney" To: Lan Tianyu Cc: rjw@rjwysocki.net, viresh.kumar@linaro.org, dipankar@in.ibm.com, fweisbec@gmail.com, youquan.song@intel.com, riel@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] Tick: Introduce tick_nohz_check() to check nohz enable status Message-ID: <20131029095135.GH4126@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1383036537-30362-1-git-send-email-tianyu.lan@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1383036537-30362-1-git-send-email-tianyu.lan@intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13102909-7182-0000-0000-000008ED96DB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3339 Lines: 90 On Tue, Oct 29, 2013 at 04:48:56PM +0800, Lan Tianyu wrote: > In some cases, nohz enable status needs to be checked. E.G, in RCU and cpufreq > ondemand governor. So add tick_nohz_check() to return tick_nohz_enabled value > And use tick_nohz_check() instead of referencing tick_nohz_enabled in the rcutree_plugin.h. > > Signed-off-by: Lan Tianyu NACK on the rcutree change unless you put the ACCESS_ONCE() in. Or is there some reason that ACCESS_ONCE() is not needed? If so, what is that reason? Thanx, Paul > --- > include/linux/tick.h | 2 ++ > kernel/rcutree_plugin.h | 4 +--- > kernel/time/tick-sched.c | 8 +++++++- > 3 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/include/linux/tick.h b/include/linux/tick.h > index 5128d33..a9c5374 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -136,6 +136,7 @@ static inline int tick_nohz_tick_stopped(void) > extern void tick_nohz_idle_enter(void); > extern void tick_nohz_idle_exit(void); > extern void tick_nohz_irq_exit(void); > +extern int tick_nohz_check(void); > extern ktime_t tick_nohz_get_sleep_length(void); > extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time); > extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time); > @@ -155,6 +156,7 @@ static inline ktime_t tick_nohz_get_sleep_length(void) > > return len; > } > +static inline int tick_nohz_check(void) { return 0; } > static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; } > static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } > # endif /* !CONFIG_NO_HZ_COMMON */ > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 130c97b..af167ec 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -1627,8 +1627,6 @@ module_param(rcu_idle_gp_delay, int, 0644); > static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; > module_param(rcu_idle_lazy_gp_delay, int, 0644); > > -extern int tick_nohz_enabled; > - > /* > * Try to advance callbacks for all flavors of RCU on the current CPU. > * Afterwards, if there are any callbacks ready for immediate invocation, > @@ -1718,7 +1716,7 @@ static void rcu_prepare_for_idle(int cpu) > int tne; > > /* Handle nohz enablement switches conservatively. */ > - tne = ACCESS_ONCE(tick_nohz_enabled); > + tne = tick_nohz_check(); > if (tne != rdtp->tick_nohz_enabled_snap) { > if (rcu_cpu_has_callbacks(cpu, NULL)) > invoke_rcu_core(); /* force nohz to see update. */ > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 3612fc7..d381a22 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -361,7 +361,13 @@ void __init tick_nohz_init(void) > /* > * NO HZ enabled ? > */ > -int tick_nohz_enabled __read_mostly = 1; > +static int tick_nohz_enabled __read_mostly = 1; > + > +int tick_nohz_check(void) > +{ > + return tick_nohz_enabled; > +} > +EXPORT_SYMBOL_GPL(tick_nohz_check); > > /* > * Enable / Disable tickless mode > -- > 1.8.4.rc0.1.g8f6a3e5.dirty > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/