Messages in this thread | | | Subject | Re: [PATCH] x86: Export tsc related information in sysfs | From | john stultz <> | Date | Wed, 26 May 2010 12:49:50 -0700 |
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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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