[PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Chuansheng Liu]

Implementing one new API wake_up_if_idle(), which is used to
wake up the idle CPU.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
---
 include/linux/sched.h |    1 +
 kernel/sched/core.c   |   16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 857ba40..3f89ac1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
 extern struct sched_domain_topology_level *sched_domain_topology;
 
 extern void set_sched_topology(struct sched_domain_topology_level *tl);
+extern void wake_up_if_idle(int cpu);
 
 #ifdef CONFIG_SCHED_DEBUG
 # define SD_INIT_NAME(type)		.name = #type
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1211575..adf104f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
 	}
 }
 
+void wake_up_if_idle(int cpu)
+{
+	struct rq *rq = cpu_rq(cpu);
+	unsigned long flags;
+
+	if (set_nr_if_polling(rq->idle)) {
+		trace_sched_wake_idle_without_ipi(cpu);
+	} else {
+		raw_spin_lock_irqsave(&rq->lock, flags);
+		if (rq->curr == rq->idle)
+			smp_send_reschedule(cpu);
+		/* Else cpu is not in idle, do nothing here */
+		raw_spin_unlock_irqrestore(&rq->lock, flags);
+	}
+}
+
 bool cpus_share_cache(int this_cpu, int that_cpu)
 {
 	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
-- 
1.7.9.5

[PATCH 2/3] smp: re-implement the kick_all_cpus_sync() with wake_up_if_idle()

[Chuansheng Liu]

Currently using smp_call_function() just woke up the corresponding
cpu, but can not break the polling idle loop.

Here using the new sched API wake_up_if_idle() to implement it.

Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
---
 kernel/smp.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index aff8aa1..0b647c3 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -13,6 +13,7 @@
 #include <linux/gfp.h>
 #include <linux/smp.h>
 #include <linux/cpu.h>
+#include <linux/sched.h>
 
 #include "smpboot.h"
 
@@ -677,10 +678,6 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
 }
 EXPORT_SYMBOL(on_each_cpu_cond);
 
-static void do_nothing(void *unused)
-{
-}
-
 /**
  * kick_all_cpus_sync - Force all cpus out of idle
  *
@@ -694,8 +691,15 @@ static void do_nothing(void *unused)
  */
 void kick_all_cpus_sync(void)
 {
-	/* Make sure the change is visible before we kick the cpus */
-	smp_mb();
-	smp_call_function(do_nothing, NULL, 1);
+	int cpu;
+
+	preempt_disable();
+	for_each_online_cpu(cpu) {
+		if (cpu == smp_processor_id())
+			continue;
+
+		wake_up_if_idle(cpu);
+	}
+	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
-- 
1.7.9.5

[PATCH 3/3] cpuidle: Using the kick_all_cpus_sync() to wake up all cpus

[Chuansheng Liu]

Current latency notify callback has the same function with
kick_all_cpus_sync().

Here use it directly to remove the redundant code.

Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
---
 drivers/cpuidle/cpuidle.c |    7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index ee9df5e..7827375 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -530,11 +530,6 @@ EXPORT_SYMBOL_GPL(cpuidle_register);
 
 #ifdef CONFIG_SMP
 
-static void smp_callback(void *v)
-{
-	/* we already woke the CPU up, nothing more to do */
-}
-
 /*
  * This function gets called when a part of the kernel has a new latency
  * requirement.  This means we need to get all processors out of their C-state,
@@ -544,7 +539,7 @@ static void smp_callback(void *v)
 static int cpuidle_latency_notify(struct notifier_block *b,
 		unsigned long l, void *v)
 {
-	smp_call_function(smp_callback, NULL, 1);
+	kick_all_cpus_sync();
 	return NOTIFY_OK;
 }
 
-- 
1.7.9.5

Re: [PATCH 2/3] smp: re-implement the kick_all_cpus_sync() with wake_up_if_idle()

[Andy Lutomirski]

On Fri, Aug 15, 2014 at 12:01 AM, Chuansheng Liu
<chuansheng.liu@intel.com> wrote:
> Currently using smp_call_function() just woke up the corresponding
> cpu, but can not break the polling idle loop.
>
> Here using the new sched API wake_up_if_idle() to implement it.

kick_all_cpus_sync has other callers, and those other callers want the
old behavior.  I think this should be a new function.

--Andy

>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
> ---
>  kernel/smp.c |   18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index aff8aa1..0b647c3 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -13,6 +13,7 @@
>  #include <linux/gfp.h>
>  #include <linux/smp.h>
>  #include <linux/cpu.h>
> +#include <linux/sched.h>
>
>  #include "smpboot.h"
>
> @@ -677,10 +678,6 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
>  }
>  EXPORT_SYMBOL(on_each_cpu_cond);
>
> -static void do_nothing(void *unused)
> -{
> -}
> -
>  /**
>   * kick_all_cpus_sync - Force all cpus out of idle
>   *
> @@ -694,8 +691,15 @@ static void do_nothing(void *unused)
>   */
>  void kick_all_cpus_sync(void)
>  {
> -       /* Make sure the change is visible before we kick the cpus */
> -       smp_mb();
> -       smp_call_function(do_nothing, NULL, 1);
> +       int cpu;
> +
> +       preempt_disable();
> +       for_each_online_cpu(cpu) {
> +               if (cpu == smp_processor_id())
> +                       continue;
> +
> +               wake_up_if_idle(cpu);
> +       }
> +       preempt_enable();
>  }
>  EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
> --
> 1.7.9.5
>



-- 
Andy Lutomirski
AMA Capital Management, LLC

RE: [PATCH 2/3] smp: re-implement the kick_all_cpus_sync() with wake_up_if_idle()

[Liu, Chuansheng]

Hello Andy,

> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@amacapital.net]
> Sent: Friday, August 15, 2014 11:41 PM
> To: Liu, Chuansheng
> Cc: Peter Zijlstra; Daniel Lezcano; Rafael J. Wysocki; Ingo Molnar;
> linux-pm@vger.kernel.org; linux-kernel@vger.kernel.org; Liu, Changcheng;
> Wang, Xiaoming; Chakravarty, Souvik K
> Subject: Re: [PATCH 2/3] smp: re-implement the kick_all_cpus_sync() with
> wake_up_if_idle()
> 
> On Fri, Aug 15, 2014 at 12:01 AM, Chuansheng Liu
> <chuansheng.liu@intel.com> wrote:
> > Currently using smp_call_function() just woke up the corresponding
> > cpu, but can not break the polling idle loop.
> >
> > Here using the new sched API wake_up_if_idle() to implement it.
> 
> kick_all_cpus_sync has other callers, and those other callers want the
> old behavior.  I think this should be a new function.
> 
Yes, seems some current users of kick_all_cpus_sync() need IPI indeed,
will try to send out patch V2 with one new function.

[PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Chuansheng Liu]

Implementing one new API wake_up_if_idle(), which is used to
wake up the idle CPU.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
---
 include/linux/sched.h |    1 +
 kernel/sched/core.c   |   16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 857ba40..3f89ac1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
 extern struct sched_domain_topology_level *sched_domain_topology;
 
 extern void set_sched_topology(struct sched_domain_topology_level *tl);
+extern void wake_up_if_idle(int cpu);
 
 #ifdef CONFIG_SCHED_DEBUG
 # define SD_INIT_NAME(type)		.name = #type
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1211575..adf104f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
 	}
 }
 
+void wake_up_if_idle(int cpu)
+{
+	struct rq *rq = cpu_rq(cpu);
+	unsigned long flags;
+
+	if (set_nr_if_polling(rq->idle)) {
+		trace_sched_wake_idle_without_ipi(cpu);
+	} else {
+		raw_spin_lock_irqsave(&rq->lock, flags);
+		if (rq->curr == rq->idle)
+			smp_send_reschedule(cpu);
+		/* Else cpu is not in idle, do nothing here */
+		raw_spin_unlock_irqrestore(&rq->lock, flags);
+	}
+}
+
 bool cpus_share_cache(int this_cpu, int that_cpu)
 {
 	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
-- 
1.7.9.5

Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Daniel Lezcano]

On 08/18/2014 10:37 AM, Chuansheng Liu wrote:
> Implementing one new API wake_up_if_idle(), which is used to
> wake up the idle CPU.

Is this patchset tested ? Did you check it solves the issue you were 
facing ?

> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
> ---
>   include/linux/sched.h |    1 +
>   kernel/sched/core.c   |   16 ++++++++++++++++
>   2 files changed, 17 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 857ba40..3f89ac1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>   extern struct sched_domain_topology_level *sched_domain_topology;
>
>   extern void set_sched_topology(struct sched_domain_topology_level *tl);
> +extern void wake_up_if_idle(int cpu);
>
>   #ifdef CONFIG_SCHED_DEBUG
>   # define SD_INIT_NAME(type)		.name = #type
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1211575..adf104f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
>   	}
>   }
>
> +void wake_up_if_idle(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +
> +	if (set_nr_if_polling(rq->idle)) {
> +		trace_sched_wake_idle_without_ipi(cpu);
> +	} else {
> +		raw_spin_lock_irqsave(&rq->lock, flags);
> +		if (rq->curr == rq->idle)
> +			smp_send_reschedule(cpu);
> +		/* Else cpu is not in idle, do nothing here */
> +		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	}
> +}
> +
>   bool cpus_share_cache(int this_cpu, int that_cpu)
>   {
>   	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
>


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Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
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RE: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Liu, Chuansheng]

Hello Daniel,

> -----Original Message-----
> From: Daniel Lezcano [mailto:daniel.lezcano@linaro.org]
> Sent: Thursday, August 21, 2014 9:54 AM
> To: Liu, Chuansheng; luto@amacapital.net; peterz@infradead.org;
> rjw@rjwysocki.net; mingo@redhat.com
> Cc: linux-pm@vger.kernel.org; linux-kernel@vger.kernel.org; Liu, Changcheng;
> Wang, Xiaoming; Chakravarty, Souvik K
> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
> idle cpu
> 
> On 08/18/2014 10:37 AM, Chuansheng Liu wrote:
> > Implementing one new API wake_up_if_idle(), which is used to
> > wake up the idle CPU.
> 
> Is this patchset tested ? Did you check it solves the issue you were
> facing ?
We have done the basic test, and found the cores can exit C0 quickly with this patchset.
Basically once the _TIF_NEED_RESCHED is set, then the poll_idle() can be broken.

Please correct me if something is wrong, thanks.

> 
> > Suggested-by: Andy Lutomirski <luto@amacapital.net>
> > Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
> > ---
> >   include/linux/sched.h |    1 +
> >   kernel/sched/core.c   |   16 ++++++++++++++++
> >   2 files changed, 17 insertions(+)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 857ba40..3f89ac1 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
> >   extern struct sched_domain_topology_level *sched_domain_topology;
> >
> >   extern void set_sched_topology(struct sched_domain_topology_level *tl);
> > +extern void wake_up_if_idle(int cpu);
> >
> >   #ifdef CONFIG_SCHED_DEBUG
> >   # define SD_INIT_NAME(type)		.name = #type
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 1211575..adf104f 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct
> task_struct *p, int cpu)
> >   	}
> >   }
> >
> > +void wake_up_if_idle(int cpu)
> > +{
> > +	struct rq *rq = cpu_rq(cpu);
> > +	unsigned long flags;
> > +
> > +	if (set_nr_if_polling(rq->idle)) {
> > +		trace_sched_wake_idle_without_ipi(cpu);
> > +	} else {
> > +		raw_spin_lock_irqsave(&rq->lock, flags);
> > +		if (rq->curr == rq->idle)
> > +			smp_send_reschedule(cpu);
> > +		/* Else cpu is not in idle, do nothing here */
> > +		raw_spin_unlock_irqrestore(&rq->lock, flags);
> > +	}
> > +}
> > +
> >   bool cpus_share_cache(int this_cpu, int that_cpu)
> >   {
> >   	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
> >
> 
> 
> --
>   <http://www.linaro.org/> Linaro.org │ Open source software for ARM
> SoCs
> 
> Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
> <http://twitter.com/#!/linaroorg> Twitter |
> <http://www.linaro.org/linaro-blog/> Blog

Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Daniel Lezcano]

On 08/21/2014 04:12 AM, Liu, Chuansheng wrote:
> Hello Daniel,
>
>> -----Original Message-----
>> From: Daniel Lezcano [mailto:daniel.lezcano@linaro.org]
>> Sent: Thursday, August 21, 2014 9:54 AM
>> To: Liu, Chuansheng; luto@amacapital.net; peterz@infradead.org;
>> rjw@rjwysocki.net; mingo@redhat.com
>> Cc: linux-pm@vger.kernel.org; linux-kernel@vger.kernel.org; Liu, Changcheng;
>> Wang, Xiaoming; Chakravarty, Souvik K
>> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
>> idle cpu
>>
>> On 08/18/2014 10:37 AM, Chuansheng Liu wrote:
>>> Implementing one new API wake_up_if_idle(), which is used to
>>> wake up the idle CPU.
>>
>> Is this patchset tested ? Did you check it solves the issue you were
>> facing ?
> We have done the basic test, and found the cores can exit C0 quickly with this patchset.
> Basically once the _TIF_NEED_RESCHED is set, then the poll_idle() can be broken.
>
> Please correct me if something is wrong, thanks.

Actually, it was not clear for me if this patch was a proposal or not.

I will review it.

Thanks

   -- Daniel

>>> Suggested-by: Andy Lutomirski <luto@amacapital.net>
>>> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
>>> ---
>>>    include/linux/sched.h |    1 +
>>>    kernel/sched/core.c   |   16 ++++++++++++++++
>>>    2 files changed, 17 insertions(+)
>>>
>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>> index 857ba40..3f89ac1 100644
>>> --- a/include/linux/sched.h
>>> +++ b/include/linux/sched.h
>>> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>>>    extern struct sched_domain_topology_level *sched_domain_topology;
>>>
>>>    extern void set_sched_topology(struct sched_domain_topology_level *tl);
>>> +extern void wake_up_if_idle(int cpu);
>>>
>>>    #ifdef CONFIG_SCHED_DEBUG
>>>    # define SD_INIT_NAME(type)		.name = #type
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index 1211575..adf104f 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct
>> task_struct *p, int cpu)
>>>    	}
>>>    }
>>>
>>> +void wake_up_if_idle(int cpu)
>>> +{
>>> +	struct rq *rq = cpu_rq(cpu);
>>> +	unsigned long flags;
>>> +
>>> +	if (set_nr_if_polling(rq->idle)) {
>>> +		trace_sched_wake_idle_without_ipi(cpu);
>>> +	} else {
>>> +		raw_spin_lock_irqsave(&rq->lock, flags);
>>> +		if (rq->curr == rq->idle)
>>> +			smp_send_reschedule(cpu);
>>> +		/* Else cpu is not in idle, do nothing here */
>>> +		raw_spin_unlock_irqrestore(&rq->lock, flags);
>>> +	}
>>> +}
>>> +
>>>    bool cpus_share_cache(int this_cpu, int that_cpu)
>>>    {
>>>    	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
>>>
>>
>>
>> --
>>    <http://www.linaro.org/> Linaro.org │ Open source software for ARM
>> SoCs
>>
>> Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
>> <http://twitter.com/#!/linaroorg> Twitter |
>> <http://www.linaro.org/linaro-blog/> Blog
>


-- 
  <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
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<http://www.linaro.org/linaro-blog/> Blog

Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Andy Lutomirski]

On Aug 18, 2014 3:52 AM, "Chuansheng Liu" <chuansheng.liu@intel.com> wrote:
>
> Implementing one new API wake_up_if_idle(), which is used to
> wake up the idle CPU.
>
> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
> ---
>  include/linux/sched.h |    1 +
>  kernel/sched/core.c   |   16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 857ba40..3f89ac1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>  extern struct sched_domain_topology_level *sched_domain_topology;
>
>  extern void set_sched_topology(struct sched_domain_topology_level *tl);
> +extern void wake_up_if_idle(int cpu);
>
>  #ifdef CONFIG_SCHED_DEBUG
>  # define SD_INIT_NAME(type)            .name = #type
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1211575..adf104f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
>         }
>  }
>
> +void wake_up_if_idle(int cpu)
> +{
> +       struct rq *rq = cpu_rq(cpu);
> +       unsigned long flags;
> +
> +       if (set_nr_if_polling(rq->idle)) {
> +               trace_sched_wake_idle_without_ipi(cpu);
> +       } else {
> +

FWIW, adding:

if (rq->curr != rq->idle)
    return;

Right here could improve performance on large, mostly non-idle
systems.  It would skip the spinlock in most cases.

I don't know whether this code is relevant on systems like that, though.

 raw_spin_lock_irqsave(&rq->lock, flags);
> +               if (rq->curr == rq->idle)
> +                       smp_send_reschedule(cpu);
> +               /* Else cpu is not in idle, do nothing here */
> +               raw_spin_unlock_irqrestore(&rq->lock, flags);
> +       }
> +

--Andy

Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Peter Zijlstra]

On Mon, Aug 18, 2014 at 04:37:30PM +0800, Chuansheng Liu wrote:
> Implementing one new API wake_up_if_idle(), which is used to
> wake up the idle CPU.
> 
> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
> ---
>  include/linux/sched.h |    1 +
>  kernel/sched/core.c   |   16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 857ba40..3f89ac1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>  extern struct sched_domain_topology_level *sched_domain_topology;
>  
>  extern void set_sched_topology(struct sched_domain_topology_level *tl);
> +extern void wake_up_if_idle(int cpu);
>  
>  #ifdef CONFIG_SCHED_DEBUG
>  # define SD_INIT_NAME(type)		.name = #type
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1211575..adf104f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
>  	}
>  }
>  
> +void wake_up_if_idle(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +
> +	if (set_nr_if_polling(rq->idle)) {
> +		trace_sched_wake_idle_without_ipi(cpu);
> +	} else {
> +		raw_spin_lock_irqsave(&rq->lock, flags);
> +		if (rq->curr == rq->idle)

That needs to be is_idle_task(), there might be other 'idle' tasks than
rq->idle :/

> +			smp_send_reschedule(cpu);
> +		/* Else cpu is not in idle, do nothing here */
> +		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	}
> +}
> +
>  bool cpus_share_cache(int this_cpu, int that_cpu)
>  {
>  	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
> -- 
> 1.7.9.5
> 

Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Peter Zijlstra]

On Thu, Aug 21, 2014 at 02:21:51PM -0700, Andy Lutomirski wrote:
> On Aug 18, 2014 3:52 AM, "Chuansheng Liu" <chuansheng.liu@intel.com> wrote:

> > +void wake_up_if_idle(int cpu)
> > +{
> > +       struct rq *rq = cpu_rq(cpu);
> > +       unsigned long flags;
> > +
> > +       if (set_nr_if_polling(rq->idle)) {
> > +               trace_sched_wake_idle_without_ipi(cpu);
> > +       } else {
> > +
> 
> FWIW, adding:
> 
> if (rq->curr != rq->idle)
>     return;
> 
> Right here could improve performance on large, mostly non-idle
> systems.  It would skip the spinlock in most cases.
> 

 !is_idle_task() :-)

RE: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Liu, Chuansheng]

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@infradead.org]
> Sent: Wednesday, September 03, 2014 5:54 PM
> To: Andy Lutomirski
> Cc: Liu, Chuansheng; linux-pm@vger.kernel.org; Rafael J. Wysocki; Daniel
> Lezcano; Wang, Xiaoming; Ingo Molnar; Chakravarty, Souvik K; Liu, Changcheng;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
> idle cpu
> 
> On Thu, Aug 21, 2014 at 02:21:51PM -0700, Andy Lutomirski wrote:
> > On Aug 18, 2014 3:52 AM, "Chuansheng Liu" <chuansheng.liu@intel.com>
> wrote:
> 
> > > +void wake_up_if_idle(int cpu)
> > > +{
> > > +       struct rq *rq = cpu_rq(cpu);
> > > +       unsigned long flags;
> > > +
> > > +       if (set_nr_if_polling(rq->idle)) {
> > > +               trace_sched_wake_idle_without_ipi(cpu);
> > > +       } else {
> > > +
> >
> > FWIW, adding:
> >
> > if (rq->curr != rq->idle)
> >     return;
> >
> > Right here could improve performance on large, mostly non-idle
> > systems.  It would skip the spinlock in most cases.
> >
> 
>  !is_idle_task() :-)
Thanks Peter and Andy, will refine the patches again:)

Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Daniel Lezcano]

On 09/04/2014 09:17 AM, Chuansheng Liu wrote:
> Implementing one new API wake_up_if_idle(), which is used to
> wake up the idle CPU.
>
> Suggested-by: Andy Lutomirski <luto@amacapital.net>
> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>

Hi Chuanseng,

in the future, please prefix the patches with the version number and a 
changelog.

Thanks

   -- Daniel

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>

> ---
>   include/linux/sched.h |    1 +
>   kernel/sched/core.c   |   19 +++++++++++++++++++
>   2 files changed, 20 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 857ba40..3f89ac1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>   extern struct sched_domain_topology_level *sched_domain_topology;
>
>   extern void set_sched_topology(struct sched_domain_topology_level *tl);
> +extern void wake_up_if_idle(int cpu);
>
>   #ifdef CONFIG_SCHED_DEBUG
>   # define SD_INIT_NAME(type)		.name = #type
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1211575..b818548 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1620,6 +1620,25 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
>   	}
>   }
>
> +void wake_up_if_idle(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +
> +	if (!is_idle_task(rq->curr))
> +		return;
> +
> +	if (set_nr_if_polling(rq->idle)) {
> +		trace_sched_wake_idle_without_ipi(cpu);
> +	} else {
> +		raw_spin_lock_irqsave(&rq->lock, flags);
> +		if (is_idle_task(rq->curr))
> +			smp_send_reschedule(cpu);
> +		/* Else cpu is not in idle, do nothing here */
> +		raw_spin_unlock_irqrestore(&rq->lock, flags);
> +	}
> +}
> +
>   bool cpus_share_cache(int this_cpu, int that_cpu)
>   {
>   	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
>


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RE: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

[Liu, Chuansheng]

> -----Original Message-----
> From: Daniel Lezcano [mailto:daniel.lezcano@linaro.org]
> Sent: Thursday, September 04, 2014 8:53 PM
> To: Liu, Chuansheng; peterz@infradead.org; luto@amacapital.net;
> rjw@rjwysocki.net; mingo@redhat.com
> Cc: linux-pm@vger.kernel.org; linux-kernel@vger.kernel.org; Liu, Changcheng;
> Wang, Xiaoming; Chakravarty, Souvik K
> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
> idle cpu
> 
> On 09/04/2014 09:17 AM, Chuansheng Liu wrote:
> > Implementing one new API wake_up_if_idle(), which is used to
> > wake up the idle CPU.
> >
> > Suggested-by: Andy Lutomirski <luto@amacapital.net>
> > Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
> 
> Hi Chuanseng,
> 
> in the future, please prefix the patches with the version number and a
> changelog.
> 
Thanks your advice, Daniel, will do that next time:)