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    SubjectRe: [PATCH] x86: Export tsc related information in sysfs
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    On Wed, 2010-05-26 at 14:44 -0400, Brian Bloniarz wrote:
    > On 05/26/2010 12:25 PM, john stultz wrote:
    > > Brian: is this something the NTPd folks actually want? Has anyone
    > > checked with them before we hand down the solution from high upon on
    > > lkml mountain?
    >
    > I haven't checked, it's been a while since I dealt with
    > this problem. The NTP maintainers definitely complain about the
    > quick TSC calibration code like it's a bug:
    > (e.g. http://www.mail-archive.com/questions@lists.ntp.org/msg02079.html).
    > Anyway I'll reach out before I spend any time investing in
    > a solution that they don't want (and you don't like :).
    >
    > > Personally I think NTPd should be a little more savvy about how far it
    > > trusts the drift file when it starts up. Since I believe its
    > > fast-startup mode can quickly estimate the drift well within 100ppm,
    > > which is about the maximum variance I've seen from the calibration code.
    >
    > The workaround we went with was to remove the drift file on
    > every reboot. But in our experience, even with iburst, converging takes
    > a long time. I don't have hard numbers since it's been a long time since
    > I investigated the problem, but we defined failure as >1ms offset syncing
    > to a server in our LAN, and a cold NTP boot takes 10-20 hours to get
    > there.

    Ok. If its been awhile, you may find recent kernels (2.6.31+) are much
    faster to converge due to adjustments made to the SHIFT_PLL constant.
    This was done explicitly to address issues similar to what you describe
    above.

    thanks
    -john



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