On 2012-09-13 15:41, Maciej W. Rozycki wrote: > On Wed, 12 Sep 2012, Matthew Ogilvie wrote: > >> Also, how big of a concern is a very rare gained or lost IRQ0 >> actually? Under normal conditions, I would expect this to at most >> cause a one time clock drift in the guest OS of a fraction of >> a second. If that only happens when rebooting or migrating the >> guest... > > It depends on how you define "very rare". Once per month or probably > even per day is probably acceptable although you'll see a disruption in > the system clock. This is still likely unwanted if the system is used as > a clock reference and not just wants to keep its clock right for own > purposes. Anything more frequent and NTP does care very much; an accurate > system clock is important in many uses, starting from basic ones such as > where timestamps of files exported over NFS are concerned. > > Speaking of real hw -- I don't know whether that really matters for > emulated systems. Thanks for looking into the 8254 PIT in details. First correct, then fast. That rule applies at least to the conceptual phase. Also, for rarely used PIT modes, I would refrain from optimizing them away from the specified behaviour. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
