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s390/cputime: provide archicture specific cputime_to_nsecs 

The generic cputime_to_nsecs function first converts the cputime
to micro-seconds and then multiplies the result with 1000. This
looses some bits of accuracy, provide our own version of
cputime_to_nsecs that does not loose precision.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2017-03-01 09:21:10 +01:00
parent 3c915bdc17
commit e53051e757
1 changed files with 7 additions and 1 deletions
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8
arch/s390/include/asm/cputime.h
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@ -8,6 +8,7 @@
#define _S390_CPUTIME_H
#include <linux/types.h>
#include <asm/timex.h>
#define CPUTIME_PER_USEC 4096ULL
#define CPUTIME_PER_SEC (CPUTIME_PER_USEC * USEC_PER_SEC)
@ -17,13 +18,18 @@
#define cmpxchg_cputime(ptr, old, new) cmpxchg64(ptr, old, new)
/*
* Convert cputime to microseconds and back.
* Convert cputime to microseconds.
*/
static inline u64 cputime_to_usecs(const u64 cputime)
{
return cputime >> 12;
}
/*
* Convert cputime to nanoseconds.
*/
#define cputime_to_nsecs(cputime) tod_to_ns(cputime)
u64 arch_cpu_idle_time(int cpu);
#define arch_idle_time(cpu) arch_cpu_idle_time(cpu)