Re: [PATCH 2/2] Dynamic Tick: Allow 32-bit machines to sleep for more than 2.15 seconds

[john stultz <johnstul@us.ibm.com>]

On Wed, 2009-05-27 at 09:49 -0500, Jon Hunter wrote:
> In the dynamic tick code, "max_delta_ns" (member of the 
> "clock_event_device" structure) represents the maximum sleep time that 
> can occur between timer events in nanoseconds.
> 
> The variable, "max_delta_ns", is defined as an unsigned long which is a 
> 32-bit integer for 32-bit machines and a 64-bit integer for 64-bit 
> machines (if -m64 option is used for gcc). The value of max_delta_ns is 
> set by calling the function "clockevent_delta2ns()" which returns a 
> maximum value of LONG_MAX. For a 32-bit machine LONG_MAX is equal to 
> 0x7fffffff and in nanoseconds this equates to ~2.15 seconds. Hence, the 
> maximum sleep time for a 32-bit machine is ~2.15 seconds, where as for a 
> 64-bit machine it will be many years.
> 
> This patch changes the type of max_delta_ns to be "unsigned long long" 
> instead of "unsigned long" so that this variable is a 64-bit type for 
> both 32-bit and 64-bit machines. It also changes the maximum value 
> returned by clockevent_delta2ns() to LLONG_MAX. Hence this allows a 
> 32-bit machine to sleep for longer than ~2.15 seconds. Please note that 
> this patch changes "min_delta_ns" to be "unsigned long long" as well and 
> although this is probably unnecessary, it makes the patch simpler.
> 
> Signed-off-by: Jon Hunter <jon-hunter@ti.com>

Acked-by: John Stultz <johnstul@us.ibm.com>


> ---
>   include/linux/clockchips.h |    6 +++---
>   kernel/hrtimer.c           |    2 +-
>   kernel/time/clockevents.c  |   10 +++++-----
>   kernel/time/tick-oneshot.c |    2 +-
>   kernel/time/timer_list.c   |    4 ++--
>   5 files changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
> index 3a1dbba..8154bc6 100644
> --- a/include/linux/clockchips.h
> +++ b/include/linux/clockchips.h
> @@ -77,8 +77,8 @@ enum clock_event_nofitiers {
>   struct clock_event_device {
>   	const char		*name;
>   	unsigned int		features;
> -	unsigned long		max_delta_ns;
> -	unsigned long		min_delta_ns;
> +	unsigned long long	max_delta_ns;
> +	unsigned long long	min_delta_ns;
>   	unsigned long		mult;
>   	int			shift;
>   	int			rating;
> @@ -116,7 +116,7 @@ static inline unsigned long div_sc(unsigned long 
> ticks, unsigned long nsec,
>   }
> 
>   /* Clock event layer functions */
> -extern unsigned long clockevent_delta2ns(unsigned long latch,
> +extern unsigned long long clockevent_delta2ns(unsigned long latch,
>   					 struct clock_event_device *evt);
>   extern void clockevents_register_device(struct clock_event_device *dev);
> 
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index cb8a15c..5b1cdc4 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1199,7 +1199,7 @@ hrtimer_interrupt_hanging(struct 
> clock_event_device *dev,
>   	force_clock_reprogram = 1;
>   	dev->min_delta_ns = (unsigned long)try_time.tv64 * 3;
>   	printk(KERN_WARNING "hrtimer: interrupt too slow, "
> -		"forcing clock min delta to %lu ns\n", dev->min_delta_ns);
> +		"forcing clock min delta to %llu ns\n", dev->min_delta_ns);
>   }
>   /*
>    * High resolution timer interrupt
> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
> index d13be21..3fa07b3 100644
> --- a/kernel/time/clockevents.c
> +++ b/kernel/time/clockevents.c
> @@ -36,10 +36,10 @@ static DEFINE_SPINLOCK(clockevents_lock);
>    *
>    * Math helper, returns latch value converted to nanoseconds (bound 
> checked)
>    */
> -unsigned long clockevent_delta2ns(unsigned long latch,
> +unsigned long long clockevent_delta2ns(unsigned long latch,
>   				  struct clock_event_device *evt)
>   {
> -	u64 clc = ((u64) latch << evt->shift);
> +	unsigned long long clc = ((unsigned long long) latch << evt->shift);
> 
>   	if (unlikely(!evt->mult)) {
>   		evt->mult = 1;
> @@ -49,10 +49,10 @@ unsigned long clockevent_delta2ns(unsigned long latch,
>   	do_div(clc, evt->mult);
>   	if (clc < 1000)
>   		clc = 1000;
> -	if (clc > LONG_MAX)
> -		clc = LONG_MAX;
> +	if (clc > LLONG_MAX)
> +		clc = LLONG_MAX;
> 
> -	return (unsigned long) clc;
> +	return clc;
>   }
> 
>   /**
> diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
> index 2e8de67..857087b 100644
> --- a/kernel/time/tick-oneshot.c
> +++ b/kernel/time/tick-oneshot.c
> @@ -50,7 +50,7 @@ int tick_dev_program_event(struct clock_event_device 
> *dev, ktime_t expires,
>   				dev->min_delta_ns += dev->min_delta_ns >> 1;
> 
>   			printk(KERN_WARNING
> -			       "CE: %s increasing min_delta_ns to %lu nsec\n",
> +			       "CE: %s increasing min_delta_ns to %llu nsec\n",
>   			       dev->name ? dev->name : "?",
>   			       dev->min_delta_ns << 1);
> 
> diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
> index a999b92..3bf30b4 100644
> --- a/kernel/time/timer_list.c
> +++ b/kernel/time/timer_list.c
> @@ -204,8 +204,8 @@ print_tickdevice(struct seq_file *m, struct 
> tick_device *td, int cpu)
>   		return;
>   	}
>   	SEQ_printf(m, "%s\n", dev->name);
> -	SEQ_printf(m, " max_delta_ns:   %lu\n", dev->max_delta_ns);
> -	SEQ_printf(m, " min_delta_ns:   %lu\n", dev->min_delta_ns);
> +	SEQ_printf(m, " max_delta_ns:   %llu\n", dev->max_delta_ns);
> +	SEQ_printf(m, " min_delta_ns:   %llu\n", dev->min_delta_ns);
>   	SEQ_printf(m, " mult:           %lu\n", dev->mult);
>   	SEQ_printf(m, " shift:          %d\n", dev->shift);
>   	SEQ_printf(m, " mode:           %d\n", dev->mode);