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

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Message-ID: <20200203155549.GL14914@hirez.programming.kicks-ass.net>
Date:   Mon, 3 Feb 2020 16:55:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     Randy Dunlap <rdunlap@...radead.org>, mingo@...hat.com,
        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,
        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 Mon, Feb 03, 2020 at 07:07:57AM -0500, Thara Gopinath wrote:
> 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.

Or just send an update for this patch? I'm thinking most of this is
looking good.