lkml.org 
[lkml]   [2013]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] Tick: Introduce tick_nohz_check() to check nohz enable status
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?

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
>



\
 
 \ /
  Last update: 2013-10-29 11:21    [W:0.155 / U:0.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site