linux-kernel - Re: [PATCH RFC] sched: Micro optimization in pick_next_task() and in check_preempt

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Message-ID: <20191219135350.GA2844@hirez.programming.kicks-ass.net>
Date:   Thu, 19 Dec 2019 14:53:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] sched: Micro optimization in pick_next_task() and in
 check_preempt_curr()

On Thu, Dec 19, 2019 at 08:50:42AM -0500, Steven Rostedt wrote:
> On Thu, 19 Dec 2019 15:39:14 +0300
> Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
> 
> > @@ -6569,6 +6558,11 @@ void __init sched_init(void)
> >  	unsigned long ptr = 0;
> >  	int i;
> >  
> > +	BUG_ON(&idle_sched_class > &fair_sched_class ||
> > +		&fair_sched_class > &rt_sched_class ||
> > +		&rt_sched_class > &dl_sched_class ||
> > +		&dl_sched_class > &stop_sched_class);
> > +
> 
> Can this be a BUILD_BUG_ON? These address should all be constants.

Nope, BUILD_BUG_ON() is for compile time constants, these are link time
constants.