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

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Date:   Tue, 22 Oct 2019 16:36:13 -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, kernel-team@...roid.com
Subject: Re: [Patch v3 7/7] sched: thermal: Enable tuning of decay period

On 10/22/2019 05:03 AM, Quentin Perret wrote:
> Hi Thara,
> 
> On Monday 21 Oct 2019 at 17:03:56 (-0400), Thara Gopinath wrote:
>> 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.
> 
> I'd personally prefer if it wan't a Kconfig option. We'd like to make
> Android devices (which are going to use this) work with a Generic Kernel
> Image, which means there will be a single config for everyone. But I
> expect this knob to be tuned to different values depending on the SoC.
> 
> If you really don't want a sysctl, perhaps a cmdline option could work ?
yes . I will. I have sent across v4 with these and other review comments
fixed.
> 
> Thanks,
> Quentin
> 


-- 
Warm Regards
Thara