linux-kernel - Re: [PATCH 1/3] sched: Add new API wake_up_if

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Date:	Thu, 21 Aug 2014 05:48:11 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>,
	"luto@...capital.net" <luto@...capital.net>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"mingo@...hat.com" <mingo@...hat.com>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Liu, Changcheng" <changcheng.liu@...el.com>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>,
	"Chakravarty, Souvik K" <souvik.k.chakravarty@...el.com>
Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
 idle cpu

On 08/21/2014 04:12 AM, Liu, Chuansheng wrote:
> Hello Daniel,
>
>> -----Original Message-----
>> From: Daniel Lezcano [mailto:daniel.lezcano@...aro.org]
>> Sent: Thursday, August 21, 2014 9:54 AM
>> To: Liu, Chuansheng; luto@...capital.net; peterz@...radead.org;
>> rjw@...ysocki.net; mingo@...hat.com
>> Cc: linux-pm@...r.kernel.org; linux-kernel@...r.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@...capital.net>
>>> Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.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 |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

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