>>> On 14.05.13 at 19:15, John Stultz <john.stu...@linaro.org> wrote: > On 05/14/2013 02:47 AM, David Vrabel wrote: >> On 14/05/13 01:40, John Stultz wrote: >>> I'm sorry, this isn't quite making sense to me. Could you further >>> describe the exact problematic behavior you're seeing here, and why its >>> a problem? >> The Xen wallclock is used as the persistent clock for Xen guests. This >> is initialized (by Xen) with the CMOS RTC at the start of day. > > Start of the day? I assume you mean on dom0 bootup? Or is it done > pre-dom0 bootup by Xen itself?
It is, indeed - Xen reads the CMOS clock (or consults EFI) once when it starts up, but leaves those alone as soon as it launched Dom0. >> If the >> RTC is incorrect then guests will see an incorrect wallclock time until >> dom0 has corrected it. > > > Sorry, just a bit more clarifying context here: So there is a 1:1 > relationship between xen_wall_clock and the RTC for all domN guests? And > even if dom0 has set its system time properly, domN guests will > initialize (in effect) from the hardware RTC and not from dom0's system > time? No, (PV) DomU-s will get their time from the software clock that Xen maintains, which Dom0 is helping keep in good shape when NTP-synced. So the hypervisor really doesn't care about the actual RTC getting updated in hardware, all it needs is for Dom0 to notify it of wall clock corrections. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
