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Commit 97813f2f authored by Jon Hunter's avatar Jon Hunter Committed by Thomas Gleixner
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nohz: Allow 32-bit machines to sleep for more than 2.15 seconds 



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 "u64" 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 KTIME_MAX.  Hence this allows a 32-bit
machine to sleep for longer than ~2.15 seconds. Please note that this
patch also changes "min_delta_ns" to be "u64" too and although this is
unnecessary, it makes the patch simpler as it avoids to fixup all
callers of clockevent_delta2ns().

[ tglx: changed "unsigned long long" to u64 as we use this data type
  	through out the time code ]

Signed-off-by: default avatarJon Hunter <jon-hunter@ti.com>
Cc: John Stultz <johnstul@us.ibm.com>
LKML-Reference: <1250617512-23567-3-git-send-email-jon-hunter@ti.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 27185016

include/linux/clockchips.h

+4 −4
Original line number Diff line number Diff line
@@ -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;

	u64			max_delta_ns;

	u64			min_delta_ns;

	u32			mult;

	u32			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 u64 clockevent_delta2ns(unsigned long latch,

			       struct clock_event_device *evt);

extern void clockevents_register_device(struct clock_event_device *dev);

kernel/hrtimer.c

+2 −1
Original line number Diff line number Diff line
@@ -1240,7 +1240,8 @@ 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",

	       (unsigned long long) dev->min_delta_ns);

}

/*

 * High resolution timer interrupt

kernel/time/clockevents.c

+5 −6
Original line number Diff line number Diff line
@@ -37,10 +37,9 @@ static DEFINE_SPINLOCK(clockevents_lock); 
 *

 * Math helper, returns latch value converted to nanoseconds (bound checked)

 */

unsigned long clockevent_delta2ns(unsigned long latch,

				  struct clock_event_device *evt)

u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)

{

	u64 clc = ((u64) latch << evt->shift);

	u64 clc = (u64) latch << evt->shift;



	if (unlikely(!evt->mult)) {

		evt->mult = 1;
@@ -50,10 +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 > KTIME_MAX)

		clc = KTIME_MAX;



	return (unsigned long) clc;

	return clc;

}

EXPORT_SYMBOL_GPL(clockevent_delta2ns);

kernel/time/tick-oneshot.c

+2 −2
Original line number Diff line number Diff line
@@ -50,9 +50,9 @@ 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);

			       (unsigned long long) dev->min_delta_ns << 1);



			i = 0;

		}

kernel/time/timer_list.c

+4 −2
Original line number Diff line number Diff line
@@ -204,8 +204,10 @@ 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",

		   (unsigned long long) dev->max_delta_ns);

	SEQ_printf(m, " min_delta_ns:   %llu\n",

		   (unsigned long long) dev->min_delta_ns);

	SEQ_printf(m, " mult:           %u\n", dev->mult);

	SEQ_printf(m, " shift:          %u\n", dev->shift);

	SEQ_printf(m, " mode:           %d\n", dev->mode);