Re: DragonflyBSD kernel clock improvements

From: M. Warner Losh (imp_at_bsdimp.com)
Date: 01/25/04

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    Date: Sat, 24 Jan 2004 20:45:14 -0700 (MST)
To: dillon@apollo.backplane.com

    In message: <200401242031.i0OKVD8A037265@apollo.backplane.com>
                Matthew Dillon <dillon@apollo.backplane.com> writes:
    : No apic timer. No acpi timer. No TSC garbage. none of that.

    We've found at work that while the 8254's timer tends to be the best
    universally available time keeping device, it is only as good as the
    quarts oscillator driving it. Other time keeping can be more precise.
    We've found that systems with APM disabled have a more stable NTP
    server when they are running on CPUs with TSC using the TSC
    timecounter, but about a factor of 5, mostly due to a reduced jitter
    in timestamping the PPS interrupts that we generate. Of course, we
    don't care one whit about SMP support for these systems.

    Maybe there are better ways to obtain these results. While not
    directly releated to the nanosleep work, but just another point of
    view.

    Warner
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