linux-kernel - Re: [Patch v9 7/8] sched/fair: Enable tuning of decay period

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Date:   Mon, 3 Feb 2020 07:07:57 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Randy Dunlap <rdunlap@...radead.org>, mingo@...hat.com,
        peterz@...radead.org, ionela.voinescu@....com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rui.zhang@...el.com, qperret@...gle.com, daniel.lezcano@...aro.org,
        viresh.kumar@...aro.org, rostedt@...dmis.org, will@...nel.org,
        catalin.marinas@....com, sudeep.holla@....com,
        juri.lelli@...hat.com, corbet@....net
Cc:     linux-kernel@...r.kernel.org, amit.kachhap@...il.com,
        javi.merino@...nel.org, amit.kucheria@...durent.com
Subject: Re: [Patch v9 7/8] sched/fair: Enable tuning of decay period

On 01/28/2020 06:56 PM, Randy Dunlap wrote:
> Hi,
> 
> On 1/28/20 2:36 PM, Thara Gopinath wrote:
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index e35b28e..be4147b 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -4376,6 +4376,11 @@
>>  			incurs a small amount of overhead in the scheduler
>>  			but is useful for debugging and performance tuning.
>>  
>> +	sched_thermal_decay_shift=
>> +			[KNL, SMP] Set decay shift for thermal pressure signal.
>> +			Format: integer between 0 and 10
>> +			Default is 0.
>> +
> 
> That tells an admin [or any reader] almost nothing about this kernel parameter
> or what it does.  And nothing about what unit the value is in.
> Does the value 0 disable this feature?

Thanks for the review. 0 does not disable "thermal pressure" feature. 0
means the default decay period for averaging PELT signals (which is
usually 32 but configurable) will also be applied for thermal pressure
signal. A shift will shift the default decay period.

You are right. It needs more explanation here. I will fix it and send v10.

> 
>>  	skew_tick=	[KNL] Offset the periodic timer tick per cpu to mitigate
>>  			xtime_lock contention on larger systems, and/or RCU lock
>>  			contention on all systems with CONFIG_MAXSMP set.
> 
> 
> thanks.
> 


-- 
Warm Regards
Thara