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

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Date:	Mon, 9 Sep 2013 15:46:35 +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 03:30:44PM +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'.

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