Messages in this thread | | | Date | Mon, 04 Nov 2013 11:13:12 +0800 | From | Lan Tianyu <> | Subject | Re: [PATCH 1/2] Tick: Introduce tick_nohz_check() to check nohz enable status |
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On 2013年10月29日 18:29, Lan Tianyu wrote: > 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.
Hi Paul: Does this reason make sense to you? Or you still prefer to add ACCESS_ONCE() in the new tick_nohz_check()?
> >> >> 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 >>> >> >
-- Best regards Tianyu Lan -- 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/
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