linux-kernel - Re: [RFC PATCH v2 6/8] cpuidle: make fast idle threshold tunable

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Message-ID: <d039059f-5ff4-780e-5865-8361315896c5@linux.intel.com>
Date:   Mon, 16 Oct 2017 14:00:45 +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 6/8] cpuidle: make fast idle threshold tunable

On 2017/10/14 8:59, Rafael J. Wysocki wrote:
> On Saturday, September 30, 2017 9:20:32 AM CEST Aubrey Li wrote:
>> Add a knob to make fast idle threshold tunable
>>
>> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> 
> I first of all am not sure about the need to add a tunable for this at all
> in the first place.

Actually I think a fixed value(10) might be good enough but not quite sure
if there is a requirement to tune it for different scenario, for example even
if the predicted idle interval is 100x overhead, I still want a fast path for
a better benchmark score?

>> @@ -1229,6 +1230,17 @@ static struct ctl_table kern_table[] = {
>>  		.extra2		= &one,
>>  	},
>>  #endif
>> +#ifdef CONFIG_CPU_IDLE
>> +	{
>> +		.procname       = "fast_idle_ratio",
>> +		.data           = &sysctl_fast_idle_ratio,
>> +		.maxlen         = sizeof(int),
>> +		.mode           = 0644,
>> +		.proc_handler   = proc_dointvec_minmax,
>> +		.extra1         = &one,
>> +		.extra2         = &one_hundred,
>> +	},
>> +#endif
>>  	{ }
>>  };
>>  
> 
> And if there is a good enough reason to add it, shouldn't the tunable be
> there in the cpuidle framework?
> 
sure, if it makes sense, I'll move it into cpuidle/sysfs.c

Thanks,
-Aubrey