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

[Jon Hunter]

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@xxxxxx>
---
 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);
--
1.6.1
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