linux-kernel - Re: [PATCH V4 3/3] time/cpuidle:Handle failed call to BROADCAST_ENTER on archs with CPUIDLE_FLAG_TIMER

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Message-ID: <4923497.uFDEGdljgG@vostro.rjw.lan>
Date:	Fri, 07 Feb 2014 13:07:36 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	linux-pm@...r.kernel.org, peterz@...radead.org,
	benh@...nel.crashing.org, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	linuxppc-dev@...ts.ozlabs.org, mingo@...nel.org,
	deepthi@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	fweisbec@...il.com, paulus@...ba.org,
	srivatsa.bhat@...ux.vnet.ibm.com, svaidy@...ux.vnet.ibm.com
Subject: Re: [PATCH V4 3/3] time/cpuidle:Handle failed call to BROADCAST_ENTER on archs with CPUIDLE_FLAG_TIMER_STOP set

On Friday, February 07, 2014 01:36:52 PM Preeti U Murthy wrote:
> Some archs set the CPUIDLE_FLAG_TIMER_STOP flag for idle states in which the
> local timers stop. The cpuidle_idle_call() currently handles such idle states
> by calling into the broadcast framework so as to wakeup CPUs at their next
> wakeup event. With the hrtimer mode of broadcast, the BROADCAST_ENTER call
> into the broadcast frameowork can fail for archs that do not have an external
> clock device to handle wakeups and the CPU in question has to thus be made
> the stand by CPU. This patch handles such cases by failing the call into
> cpuidle so that the arch can take some default action. The arch will certainly
> not enter a similar idle state because a failed cpuidle call will also implicitly
> indicate that the broadcast framework has not registered this CPU to be woken up.
> Hence we are safe if we fail the cpuidle call.
> 
> In the process move the functions that trace idle statistics just before and
> after the entry and exit into idle states respectively. In other
> scenarios where the call to cpuidle fails, we end up not tracing idle
> entry and exit since a decision on an idle state could not be taken. Similarly
> when the call to broadcast framework fails, we skip tracing idle statistics
> because we are in no further position to take a decision on an alternative
> idle state to enter into.
> 
> Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
> 
>  drivers/cpuidle/cpuidle.c |   14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index a55e68f..8beb0f02 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -140,12 +140,14 @@ int cpuidle_idle_call(void)
>  		return 0;
>  	}
>  
> -	trace_cpu_idle_rcuidle(next_state, dev->cpu);
> -
>  	broadcast = !!(drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP);
>  
> -	if (broadcast)
> -		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
> +	if (broadcast &&
> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
> +		return -EBUSY;
> +
> +
> +	trace_cpu_idle_rcuidle(next_state, dev->cpu);
>  
>  	if (cpuidle_state_is_coupled(dev, drv, next_state))
>  		entered_state = cpuidle_enter_state_coupled(dev, drv,
> @@ -153,11 +155,11 @@ int cpuidle_idle_call(void)
>  	else
>  		entered_state = cpuidle_enter_state(dev, drv, next_state);
>  
> +	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> +
>  	if (broadcast)
>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
>  
> -	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> -
>  	/* give the governor an opportunity to reflect on the outcome */
>  	if (cpuidle_curr_governor->reflect)
>  		cpuidle_curr_governor->reflect(dev, entered_state);
> 
> --
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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