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Message-ID: <1395134743.4883.72.camel@marge.simpson.net>
Subject: Re: [PATCH] sched: Initialize rq->age_stamp on processor start
From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: minyard@acm.org, linux-kernel@vger.kernel.org,
        Corey Minyard <cminyard@mvista.com>
Date: Tue, 18 Mar 2014 10:25:43 +0100
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On Tue, 2014-03-18 at 09:56 +0100, Peter Zijlstra wrote: 
> On Tue, Mar 18, 2014 at 05:06:26AM +0100, Mike Galbraith wrote:

> > > +static void __cpuinit set_cpu_rq_start_time(void)
> > > +{
> > > +	int cpu = smp_processor_id();
> > > +	struct rq *rq = cpu_rq(cpu);
> > > +	rq->age_stamp = sched_clock_cpu(cpu);
> > > +}
> > 
> > rq->age_stamp must lag rq->clock.  See scale_rt_power(), and what
> > happens when it munches magic timewarp mushrooms.
> > 
> > > +
> > >  static int sched_cpu_active(struct notifier_block *nfb,
> > >  				      unsigned long action, void *hcpu)
> > >  {
> > >  	switch (action & ~CPU_TASKS_FROZEN) {
> > >  	case CPU_STARTING:
> > > +		set_cpu_rq_start_time();
> > > +		/* fall through */
> > >  	case CPU_DOWN_FAILED:
> > >  		set_cpu_active((long)hcpu, true);
> > >  		return NOTIFY_OK;
> > > @@ -6922,6 +6931,7 @@ void __init sched_init(void)
> > >  	init_sched_fair_class();
> > >  
> > >  	scheduler_running = 1;
> > > +	set_cpu_rq_start_time();
> 
> I would put it one line up; that scheduler_running=1 is the last thing
> we should do.

And set clock and age, dazed scale_rt_power() is butt ugly.

-Mike