linux-kernel - Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue

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Message-ID: <20170602182621.gnpjs4fpvwze2hfr@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Jun 2017 20:26:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rohit Jain <rohit.k.jain@...cle.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        vincent.guittot@...aro.org, morten.rasmussen@....com,
        dietmar.eggemann@....com, Dhaval Giani <dhaval.giani@...cle.com>
Subject: Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue

On Fri, Jun 02, 2017 at 11:20:20AM -0700, Rohit Jain wrote:
> 
> On 06/01/2017 05:37 AM, Peter Zijlstra wrote:
> > On Thu, Jun 01, 2017 at 02:28:27PM +0200, Peter Zijlstra wrote:
> > > On Wed, May 31, 2017 at 03:19:46PM -0700, Rohit Jain wrote:
> > > 
> > > > > > 2) This scaled capacity is normalized and mapped into buckets.
> > > > > Why?
> > And its not at all clear why you'd need
> > that to begin with.
> 
> Here is the problem I am trying to solve:
> 
> The benchmark(s) have a high degree of variance when run multiple
> times.
> 
> We believe it is because of the scheduler not being aware of the scaled
> down capacity of the CPUs because of IRQ/RT activity.
> 
> This patch helps in solving the above problem. Do you have any thoughts
> on solving this problem in any other way?

Why does determining if a CPU's capacity is scaled down need to involve
global data? AFAICT its a purely CPU local affair.