linux-kernel - Re: [RFC PATCH v2 4/8] tick/nohz: keep tick on for a fast idle

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Date:   Mon, 16 Oct 2017 11:26:11 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Aubrey Li <aubrey.li@...el.com>
Cc:     tglx@...utronix.de, peterz@...radead.org, len.brown@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 4/8] tick/nohz: keep tick on for a fast idle

On 2017/10/14 8:51, Rafael J. Wysocki wrote:
> On Saturday, September 30, 2017 9:20:30 AM CEST Aubrey Li wrote:
>> If the next idle is expected to be a fast idle, we should keep tick
>> on before going into idle
>>
>> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> 
> This also can be merged with the previous patch (and the [2/8]) IMO.
> 

okay, will merge in the next version.

>> ---
>>  drivers/cpuidle/cpuidle.c | 14 ++++++++++++++
>>  include/linux/cpuidle.h   |  2 ++
>>  kernel/time/tick-sched.c  |  4 ++++
>>  3 files changed, 20 insertions(+)
>>
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index ef6f7dd..6cb7e17 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -370,6 +370,20 @@ void cpuidle_predict(void)
>>  }
>>  
>>  /**
>> + * cpuidle_fast_idle - predict whether or not the coming idle is a fast idle
>> + * This function can be called in irq exit path, make it as soon as possible
>> + */
>> +bool cpuidle_fast_idle(void)
>> +{
>> +	struct cpuidle_device *dev = cpuidle_get_device();
>> +
>> +	if (!dev)
>> +		return false;
>> +
>> +	return dev->idle_stat.fast_idle;
> 
> return dev && dev->idle_stat.fast_idle;

Thanks!

>>  
>> @@ -916,6 +917,9 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
>>  			return false;
>>  	}
>>  
>> +	if (cpuidle_fast_idle())
>> +		return false;
>> +
>>  	return true;
> 
> return !cpuidle_fast_idle();

And thanks!
> 
>>  }
>>  
>>
> 
> And IMO there is quite a bit too much marketing in the "fast_idle" name,
> as it seems all about avoiding to stop the tick if the predicted idle
> duration is short enough.
> 

okay, and what's your suggestion? :)
I'll try to move quiet_vmstat() into the normal idle branch if this patch series
are reasonable. Is fast_idle a good indication for it?

Thanks,
-Aubrey