Re: gettimeofday resolution seriously degraded in test9

From: Peter Chubb
Date: Wed Oct 29 2003 - 17:53:59 EST


>>>>> "Stephen" == Stephen Hemminger <shemminger@xxxxxxxx> writes:

Stephen> On Wed, 29 Oct 2003 11:07:45 +0100 Gabriel Paubert
Stephen> <paubert@xxxxxxx> wrote:
>> for example.

Stephen> The suggestion of using time interpolation (like ia64) would
Stephen> make the discontinuities smaller, but still relying on fine
Stephen> grain gettimeofday for controlling servo loops with NTP
Stephen> running seems risky. Perhaps what you want to use is the
Stephen> monotonic_clock which gives better resolution (nanoseconds)
Stephen> and doesn't get hit by NTP.

monotonic_clock:
-- isn't implemented for most architectures
-- even for X86 only works for some timing sources
-- and for the most common case is variable rate because of
power management functions changing the TSC clock rate.

As far as I know, there isn't a constant-rate monotonic clock
available at present for all architectures in the linux kernel. The
nearest thing is scheduler_clock().

Peter C
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/