Messages in this thread | | | Date | Tue, 29 Oct 2013 18:29:53 +0800 | From | Lan Tianyu <> | Subject | Re: [PATCH 1/2] Tick: Introduce tick_nohz_check() to check nohz enable status |
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On 10/29/2013 05:51 PM, Paul E. McKenney wrote: > 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.lan@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?
Hi Paul:
Thanks for review. When I change this code, I find the tick_nohz_enabled isn't changed dynamically. It's only changed during parsing kernel params when "nohz=off/on" is set. Except this, it will not be changed. So I ignored ACCESS_ONCE(). If necessary, I can add it back.
> > 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 >> >
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