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nohz: Allow 32-bit machines to sleep for more than 2.15 seconds

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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>
This commit is contained in:
Jon Hunter 2009-08-18 12:45:11 -05:00 • committed by Thomas Gleixner
parent 27185016b8
commit 97813f2fe7
5 changed files with 17 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

8
include/linux/clockchips.h
View file

@ -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;
@ -116,8 +116,8 @@ static inline unsigned long div_sc(unsigned long ticks, unsigned long nsec,
}
/* Clock event layer functions */
extern unsigned long clockevent_delta2ns(unsigned long latch,
struct clock_event_device *evt);
extern u64 clockevent_delta2ns(unsigned long latch,
struct clock_event_device *evt);
extern void clockevents_register_device(struct clock_event_device *dev);
extern void clockevents_exchange_device(struct clock_event_device *old,