Hi, On Thursday 01 November 2007, Ralf Baechle wrote:
> 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. The basic idea is to provide a base frequency adjustment, when I wrote this I already wasn't entirely happy that it was hardcoded like this, but in the end I simply reimplemented what the old code did. It's not strictly needed, so if someone wants to add something like: #ifndef CLOCK_TICK_RATE #define CLOCK_TICK_ADJUST 0 #else ... it would be fine with me. bye, Roman - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/