Am Thu, 13 Dec 2018 03:41:44 -0700 schrieb "Jan Beulich" <jbeul...@suse.com>:
> And further argumentation that everyone is using NTP anyway > doesn't make it any better, when it's no-where written down that > Xen is unusable with NTP running in all guests (I'm exaggerating > here just to get the point over). Don't forget that e.g. with > XenoLinux'es independent-wallclock setting defaulting to false, we've > been suggesting that people _don't_ need to use NTP inside their > (admittedly PV) guests. IOW - your change may not break people > not using NTP. Hence I don't think the mode you introduce can be > a default-on one, which in turn means a per-domain or at least > global enable control is needed (as over previous iterations we > seem to have been agreeing). Regarding the possible unexpected drift if NTP is not used, and the domU uses TSC as clocksource anyway: If one host is on one edge of the assumed cpu_khz value and the other host is on the opposite edge, and the range will be 200 as it is in my patch, the daily drift on a 2.3GHz host would be 7.4seconds per day. This number is based on the fact that 200kz happen within a time span of 86us, which I think is correct. The question is, how much drift can be tolerated even without my patch. Looking through 5 different hosts I use, the range is between -11 and +22, and it happens to be +56 on my Laptop. So even that host with a calculated drift of +22 would be off by 2 seconds per day if ntpd would not run. Olaf
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