Re: [PATCH/RFC] clockevents: Ignore C3STOP when CPUIdle is disabled

[Daniel Lezcano]

On 06/18/2013 09:17 AM, Magnus Damm wrote:
> From: Magnus Damm <damm@xxxxxxxxxxxxx>
> 
> Introduce the function tick_device_may_c3stop() that
> ignores the C3STOP flag in case CPUIdle is disabled.
> 
> The C3STOP flag tells the system that a clock event
> device may be stopped during deep sleep, but if this
> will happen or not depends on things like if CPUIdle
> is enabled and if a CPUIdle driver is available.
> 
> This patch assumes that if CPUIdle is disabled then
> the sleep mode triggering C3STOP will never be entered.
> So by ignoring C3STOP when CPUIdle is disabled then it
> becomes possible to use high resolution timers with only
> per-cpu local timers - regardless if they have the
> C3STOP flag set or not.
> 
> Observed on the r8a73a4 SoC that at this point only uses
> ARM architected timers for clock event and clock sources.
> 
> Without this patch high resolution timers are run time
> disabled on the r8a73a4 SoC - this regardless of CPUIdle
> is disabled or not.
> 
> The less short term fix is to add support for more timers
> on the r8a73a4 SoC, but until CPUIdle support is enabled
> it must be possible to use high resoultion timers without
> additional timers.
> 
> I'd like to hear some feedback and also test this on more
> systems before merging the code, see the non-SOB below.

Do we need a broadcast timer when cpuidle is not compiled in the kernel ?

> Not-Yet-Signed-off-by: Magnus Damm <damm@xxxxxxxxxxxxx>
> ---
> 
>  An earlier ARM arch timer specific version of this patch was
>  posted yesterday as:
>  "[PATCH/RFC] arm: arch_timer: Do not set C3STOP in case CPU_IDLE=n"
> 
>  Many thanks to Mark Rutland for his kind feedback.
> 
>  kernel/time/tick-broadcast.c |    8 ++++----
>  kernel/time/tick-common.c    |    2 +-
>  kernel/time/tick-internal.h  |   11 +++++++++++
>  3 files changed, 16 insertions(+), 5 deletions(-)
> 
> --- 0001/kernel/time/tick-broadcast.c
> +++ work/kernel/time/tick-broadcast.c	2013-06-18 15:36:21.000000000 +0900
> @@ -71,7 +71,7 @@ int tick_check_broadcast_device(struct c
>  	if ((dev->features & CLOCK_EVT_FEAT_DUMMY) ||
>  	    (tick_broadcast_device.evtdev &&
>  	     tick_broadcast_device.evtdev->rating >= dev->rating) ||
> -	     (dev->features & CLOCK_EVT_FEAT_C3STOP))
> +	     tick_device_may_c3stop(dev))
>  		return 0;
>  
>  	clockevents_exchange_device(tick_broadcast_device.evtdev, dev);
> @@ -146,7 +146,7 @@ int tick_device_uses_broadcast(struct cl
>  		 * feature and the cpu is marked in the broadcast mask
>  		 * then clear the broadcast bit.
>  		 */
> -		if (!(dev->features & CLOCK_EVT_FEAT_C3STOP)) {
> +		if (!tick_device_may_c3stop(dev)) {
>  			int cpu = smp_processor_id();
>  			cpumask_clear_cpu(cpu, tick_broadcast_mask);
>  			tick_broadcast_clear_oneshot(cpu);
> @@ -270,7 +270,7 @@ static void tick_do_broadcast_on_off(uns
>  	/*
>  	 * Is the device not affected by the powerstate ?
>  	 */
> -	if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP))
> +	if (!dev || !tick_device_may_c3stop(dev))
>  		goto out;
>  
>  	if (!tick_device_is_functional(dev))
> @@ -568,7 +568,7 @@ void tick_broadcast_oneshot_control(unsi
>  	td = &per_cpu(tick_cpu_device, cpu);
>  	dev = td->evtdev;
>  
> -	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
> +	if (!tick_device_may_c3stop(dev))
>  		return;
>  
>  	bc = tick_broadcast_device.evtdev;
> --- 0001/kernel/time/tick-common.c
> +++ work/kernel/time/tick-common.c	2013-06-18 15:36:29.000000000 +0900
> @@ -52,7 +52,7 @@ int tick_is_oneshot_available(void)
>  
>  	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
>  		return 0;
> -	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
> +	if (!tick_device_may_c3stop(dev))
>  		return 1;
>  	return tick_broadcast_oneshot_available();
>  }
> --- 0001/kernel/time/tick-internal.h
> +++ work/kernel/time/tick-internal.h	2013-06-18 15:40:10.000000000 +0900
> @@ -141,6 +141,17 @@ static inline int tick_device_is_functio
>  	return !(dev->features & CLOCK_EVT_FEAT_DUMMY);
>  }
>  
> +/*
> + * Check, if the device has C3STOP behavior and CPU Idle is enabled
> + */
> +static inline bool tick_device_may_c3stop(struct clock_event_device *dev)
> +{
> +	/* The C3 sleep mode can only trigger when CPU Idle is enabled,
> +	 * so if CPU Idle is disabled then the C3STOP flag can be ignored */
> +	return (IS_ENABLED(CONFIG_CPU_IDLE) &&
> +		(dev->features & CLOCK_EVT_FEAT_C3STOP));
> +}
> +
>  #endif
>  
>  extern void do_timer(unsigned long ticks);
> --
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