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Date: Wed, 27 May 2009 11:16:16 -0700
From: john stultz <johnstul@...ibm.com>
To: Jon Hunter <jon-hunter@...com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 2/2] Dynamic Tick: Allow 32-bit machines to sleep for
more than 2.15 seconds
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@...com>
Acked-by: John Stultz <johnstul@...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);
--
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