4ff4b9e19a
We have a bug in the calculation of the next jiffie to trigger the RTC synchronisation. The aim here is to run sync_cmos_clock() as close as possible to the middle of a second. Which means we want this function to be called less than or equal to half a jiffie away from when now.tv_nsec equals 5e8 (500000000). If this is not the case for a given call to the function, for this purpose instead of updating the RTC we calculate the offset in nanoseconds to the next point in time where now.tv_nsec will be equal 5e8. The calculated offset is then converted to jiffies as these are the unit used by the timer. Hovewer timespec_to_jiffies() used here uses a ceil()-type rounding mode, where the resulting value is rounded up. As a result the range of now.tv_nsec when the timer will trigger is from 5e8 to 5e8 + TICK_NSEC rather than the desired 5e8 - TICK_NSEC / 2 to 5e8 + TICK_NSEC / 2. As a result if for example sync_cmos_clock() happens to be called at the time when now.tv_nsec is between 5e8 + TICK_NSEC / 2 and 5e8 to 5e8 + TICK_NSEC, it will simply be rescheduled HZ jiffies later, falling in the same range of now.tv_nsec again. Similarly for cases offsetted by an integer multiple of TICK_NSEC. This change addresses the problem by subtracting TICK_NSEC / 2 from the nanosecond offset to the next point in time where now.tv_nsec will be equal 5e8, effectively shifting the following rounding in timespec_to_jiffies() so that it produces a rounded-to-nearest result. Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> |
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| .. | ||
| clockevents.c | ||
| clocksource.c | ||
| jiffies.c | ||
| Kconfig | ||
| Makefile | ||
| ntp.c | ||
| tick-broadcast.c | ||
| tick-common.c | ||
| tick-internal.h | ||
| tick-oneshot.c | ||
| tick-sched.c | ||
| timekeeping.c | ||
| timer_list.c | ||
| timer_stats.c | ||