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sched, time: Define nsecs_to_jiffies() 

Use of msecs_to_jiffies() for nsecs_to_cputime() have some
problems:

 - The type of msecs_to_jiffies()'s argument is unsigned int, so
   it cannot convert msecs greater than UINT_MAX = about 49.7 days.

 - msecs_to_jiffies() returns MAX_JIFFY_OFFSET if MSB of argument
   is set, assuming that input was negative value.  So it cannot
   convert msecs greater than INT_MAX = about 24.8 days too.

This patch defines a new function nsecs_to_jiffies() that can
deal greater values, and that can deal all incoming values as
unsigned.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Spencer Candland <spencer@bluehost.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Amrico Wang <xiyou.wangcong@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <johnstul@linux.vnet.ibm.com>
LKML-Reference: <4B0E16E7.5070307@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Hidetoshi Seto 2009-11-26 14:49:27 +09:00 committed by Ingo Molnar
parent d5b7c78e97
commit b7b20df91d
3 changed files with 32 additions and 2 deletions
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1
include/linux/jiffies.h
View File

@ -307,6 +307,7 @@ extern clock_t jiffies_to_clock_t(long x);
extern unsigned long clock_t_to_jiffies(unsigned long x);
extern u64 jiffies_64_to_clock_t(u64 x);
extern u64 nsec_to_clock_t(u64 x);
extern unsigned long nsecs_to_jiffies(u64 n);
#define TIMESTAMP_SIZE 30

3
kernel/sched.c
View File

@ -5192,8 +5192,7 @@ void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
#else
#ifndef nsecs_to_cputime
# define nsecs_to_cputime(__nsecs) \
msecs_to_cputime(div_u64((__nsecs), NSEC_PER_MSEC))
# define nsecs_to_cputime(__nsecs) nsecs_to_jiffies(__nsecs)
#endif
void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)

30
kernel/time.c
View File

@ -662,6 +662,36 @@ u64 nsec_to_clock_t(u64 x)
#endif
}
/**
* nsecs_to_jiffies - Convert nsecs in u64 to jiffies
*
* @n: nsecs in u64
*
* Unlike {m,u}secs_to_jiffies, type of input is not unsigned int but u64.
* And this doesn't return MAX_JIFFY_OFFSET since this function is designed
* for scheduler, not for use in device drivers to calculate timeout value.
*
* note:
* NSEC_PER_SEC = 10^9 = (5^9 * 2^9) = (1953125 * 512)
* ULLONG_MAX ns = 18446744073.709551615 secs = about 584 years
*/
unsigned long nsecs_to_jiffies(u64 n)
{
#if (NSEC_PER_SEC % HZ) == 0
/* Common case, HZ = 100, 128, 200, 250, 256, 500, 512, 1000 etc. */
return div_u64(n, NSEC_PER_SEC / HZ);
#elif (HZ % 512) == 0
/* overflow after 292 years if HZ = 1024 */
return div_u64(n * HZ / 512, NSEC_PER_SEC / 512);
#else
/*
* Generic case - optimized for cases where HZ is a multiple of 3.
* overflow after 64.99 years, exact for HZ = 60, 72, 90, 120 etc.
*/
return div_u64(n * 9, (9ull * NSEC_PER_SEC + HZ / 2) / HZ);
#endif
}
#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void)
{