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

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Message-ID: <20170530122831.5fyywtplq4jawj3j@hirez.programming.kicks-ass.net>
Date:   Tue, 30 May 2017 14:28:31 +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
Subject: Re: [PATCH] sched: Introduce scaled capacity awareness in enqueue

On Mon, May 22, 2017 at 01:48:14PM -0700, Rohit Jain wrote:
> The patch introduces capacity awarness in scheduler (CAS) which avoids
> CPUs which might have their capacities reduced (due to IRQ/RT activity)
> when trying to schedule threads (on the push side) in the system. This
> awareness has been added into the fair scheduling class.
> 
> It does so by, using the following algorithm:
> --------------------------------------------------------------------------
> 1) As in rt_avg the scaled capacities are already calculated.
> 
> 2) This scaled capacity is normalized and mapped into buckets.

Why?

> 3) Any CPU which lies below the 80th percentile in terms of percentage
> capacity available is considered as a low capacity CPU.

Random number; can we do better? What does existing code do?