linux-kernel - Re: [PATCH 2/3] clockevents: Restart clockevent device before using it again

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Message-ID: <20150402133403.GY23123@twins.programming.kicks-ass.net>
Date:	Thu, 2 Apr 2015 15:34:03 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	Kevin Hilman <khilman@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 2/3] clockevents: Restart clockevent device before using
 it again

On Fri, Mar 27, 2015 at 10:44:28PM +0530, Viresh Kumar wrote:
> Only hrtimer_reprogram() is responsible for programming the clockevent device
> for next event, if the clockevent device is stopped earlier. And updating that
> alone is sufficient here.

> +++ b/kernel/time/hrtimer.c
> @@ -566,6 +566,7 @@ static int hrtimer_reprogram(struct hrtimer *timer,
>  {
>  	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
>  	ktime_t expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
> +	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
>  	int res;
>  
>  	WARN_ON_ONCE(hrtimer_get_expires_tv64(timer) < 0);
> @@ -610,6 +611,10 @@ static int hrtimer_reprogram(struct hrtimer *timer,
>  	if (cpu_base->hang_detected)
>  		return 0;
>  
> +	/* Switchback to ONESHOT state */
> +	if (unlikely(dev->state == CLOCK_EVT_STATE_ONESHOT_STOPPED))
> +		clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT);
> +
>  	/*
>  	 * Clockevents returns -ETIME, when the event was in the past.
>  	 */

Should we not do this in tick_program_event() instead? Note that there
are a few more places that call that, the two in the hrtimer_interrupt()
should be safe because if we're handling the interrupt its cannot be
stopped anyhow.

hrtimer_force_reprogram() seems to need the annotation regardless.

Furthermore, by putting it in tick_program_event() you also don't need
to fixup tick_nohz_restart().

Or am I completely missing something?
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