linux-kernel - Re: [Patch v3 7/7] sched: thermal: Enable tuning of decay period

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Date:   Mon, 21 Oct 2019 17:03:56 -0400
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     mingo@...hat.com, peterz@...radead.org, ionela.voinescu@....com,
        vincent.guittot@...aro.org, rui.zhang@...el.com,
        edubezval@...il.com, linux-kernel@...r.kernel.org,
        amit.kachhap@...il.com, javi.merino@...nel.org,
        daniel.lezcano@...aro.org
Subject: Re: [Patch v3 7/7] sched: thermal: Enable tuning of decay period

Hi Quentin,

Thanks for the review.
On 10/15/2019 06:14 AM, Quentin Perret wrote:
> Hi Thara,
> 
> On Sunday 13 Oct 2019 at 20:58:25 (-0400), Thara Gopinath wrote:
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 00fcea2..5056c08 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -376,6 +376,13 @@ static struct ctl_table kern_table[] = {
>>  		.mode		= 0644,
>>  		.proc_handler	= proc_dointvec,
>>  	},
>> +	{
>> +		.procname	= "sched_thermal_decay_coeff",
>> +		.data		= &sysctl_sched_thermal_decay_coeff,
>> +		.maxlen		= sizeof(unsigned int),
>> +		.mode		= 0644,
>> +		.proc_handler	= proc_dointvec,
> 
> Perhaps change this for 'sched_proc_update_handler' with min and max
> values ? Otherwise userspace is allowed to write nonsensical values
> here. And since sysctl_sched_thermal_decay_coeff is used to shift, this
> can lead to an undefined behaviour.
Will do
> 
> Also, could we take this sysctl out of SCHED_DEBUG ? I expect this to be
> used/tuned on production devices where SCHED_DEBUG should theoretically
> be off.

I will take it out of SCHED_DEBUG. I am wondering if this should be
a runtime control at all. Because this is a shift this changes the
accumulating window for the thermal pressure signal. A runtime change
will not guarantee a clean start of the window. May be I should make
this a config option.

> 
> Thanks,
> Quentin
> 


-- 
Warm Regards
Thara