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 <[email protected]>
---
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
Current, od_init() uses get_cpu_idle_time_us() to check whether
idle micro accouting is supported. The get_cpu_idle_time_us()
returns -1 only when tick nohz is disabled. This patch is to use
tick_nohz_check() directly to check nohz enable status instead of
get_cpu_idle_time_us(). This can avoid unnecessary getting and
putting cpu.
Signed-off-by: Lan Tianyu <[email protected]>
---
drivers/cpufreq/cpufreq_ondemand.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 32f26f6..79986a9 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -485,10 +485,7 @@ static int od_init(struct dbs_data *dbs_data)
return -ENOMEM;
}
- cpu = get_cpu();
- idle_time = get_cpu_idle_time_us(cpu, NULL);
- put_cpu();
- if (idle_time != -1ULL) {
+ if (tick_nohz_check()) {
/* Idle micro accounting is supported. Use finer thresholds */
tuners->up_threshold = MICRO_FREQUENCY_UP_THRESHOLD;
/*
--
1.8.4.rc0.1.g8f6a3e5.dirty
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 <[email protected]>
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
>
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 <[email protected]>
>
> 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
>>
>