linux-kernel - Re: [PATCH 13/23] sched,ion: Convert to sched_set

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Date:   Wed, 22 Apr 2020 17:39:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Qais Yousef <qais.yousef@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 13/23] sched,ion: Convert to sched_set_normal()

On Wed, Apr 22, 2020 at 05:09:15PM +0200, Vincent Guittot wrote:
> > It's not unbounded, like a true idle-time scheduler would be, but it can
> > still be pretty horrible. nice19 has some of that too of course, but
> > idle has it worse, esp. also because it begs others to preempt it.
> 
> Yeah... you have to pay the benefit of letting other tasks to preempt
> faster. But both sched_idle and nice19 have the same weight 

#define WEIGHT_IDLEPRIO		3

 /*  15 */        36,        29,        23,        18,        15,

15 != 3

Also, like said elsewhere, idle is much more eager to let itself be
preempted.