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: Jon 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: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 5 insertions, 6 deletions

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 620b58abdc32..05e8aeedcdf3 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -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);