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 <tianyu....@intel.com>
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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/