kernel/time/ntp.c contains the following piece of code:
#define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
#define CLOCK_TICK_ADJUST (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \
(s64)CLOCK_TICK_RATE)
static void ntp_update_frequency(void)
{
u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
<< TICK_LENGTH_SHIFT;
second_length += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
tick_length_base = second_length;
do_div(second_length, HZ);
tick_nsec = second_length >> TICK_LENGTH_SHIFT;
do_div(tick_length_base, NTP_INTERVAL_FREQ);
}
So it uses CLOCK_TICK_RATE which on many systems but not all is defined to
the i8253 input clock. But timekeeping on anything remotely modern makes
little use of the i8253 so I wonder the intent was here.
Ralf
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