linux-kernel - Re: [PATCH V3]hrtimer: Fix a performance regression by disable reprogramming in remove

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Date:	Wed, 11 Sep 2013 10:56:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <bitbucket@...ine.de>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>, ethan.kernel@...il.com,
	rjw@...k.pl, daniel.lezcano@...aro.org, linux-pm@...r.kernel.org,
	lenb@...nel.org
Subject: Re: [PATCH V3]hrtimer: Fix a performance regression by disable
 reprogramming in remove_hrtimer

On Mon, Sep 09, 2013 at 03:46:35PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 09, 2013 at 03:30:44PM +0200, Peter Zijlstra wrote:
> > diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> > index fa6964d..486c0ba 100644
> > --- a/drivers/idle/intel_idle.c
> > +++ b/drivers/idle/intel_idle.c
> > @@ -359,6 +359,14 @@ static int intel_idle(struct cpuidle_device *dev,
> >  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
> >  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
> >  
> > +	current_thread_into()->status |= TS_POLLING;
> > +
> > +	/*
> > +	 * Order against setting of TS_POLLING against the reading of
> > +	 * NEED_RESCHED, matched by resched_task().
> > +	 */
> > +	smp_mb();
> > +
> >  	if (!need_resched()) {
> >  
> >  		__monitor((void *)&current_thread_info()->flags, 0, 0);
> > @@ -367,6 +375,8 @@ static int intel_idle(struct cpuidle_device *dev,
> >  			__mwait(eax, ecx);
> >  	}
> >  
> > +	current_thread_into()->status &= ~TS_POLLING;
> > +
> >  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
> >  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
> 
> Hmm, arguably it would be better to set this from
> intel_idle_cpuidle_driver_init() and clear it whenever this goes away.
> Not sure how all that works, the cpuidle driver framework seems 'weird'.

OK, so I went over the idle stuff again, and we do set TS_POLLING like
stuff, it got hidden in current_{clr,set}_polling().

Still if that patch causes extra IPIs its bound to be broken in some
creative way.. I'll prod.
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