diff options
Diffstat (limited to 'kernel/time/tick-internal.h')
-rw-r--r-- | kernel/time/tick-internal.h | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h index 3548f0829e6d..649f2b48e8f0 100644 --- a/kernel/time/tick-internal.h +++ b/kernel/time/tick-internal.h @@ -177,3 +177,23 @@ void clock_was_set(unsigned int bases); void clock_was_set_delayed(void); void hrtimers_resume_local(void); + +/* Since jiffies uses a simple TICK_NSEC multiplier + * conversion, the .shift value could be zero. However + * this would make NTP adjustments impossible as they are + * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to + * shift both the nominator and denominator the same + * amount, and give ntp adjustments in units of 1/2^8 + * + * The value 8 is somewhat carefully chosen, as anything + * larger can result in overflows. TICK_NSEC grows as HZ + * shrinks, so values greater than 8 overflow 32bits when + * HZ=100. + */ +#if HZ < 34 +#define JIFFIES_SHIFT 6 +#elif HZ < 67 +#define JIFFIES_SHIFT 7 +#else +#define JIFFIES_SHIFT 8 +#endif |